For the modern version see the video KAGUYA taking "Full Earth-rise" by HDTV, 2008apr05 | 1:15.
Caption: Earth from
Apollo 17,
1972
Dec07.
Credit/Permission:
NASA,
NASA: Image #AS17-148-22742,
1972 /
Public domain.
Image link: Itself.
Caption: The Earth from Apollo 17, 1972 Dec07. This image is called The Blue Marble.
One of the few images showing a full planetary phase Earth. Blue oceans (Atlantic Ocean, Antarctic Ocean (AKA Southern Ocean), Indian Ocean), seas (Arabian Sea, Dead Sea, Mediterranean Sea, Persian Gulf, Red Sea). White clouds and anticyclones (just guessing). To the south: Antarctica, Africa, Madagascar. At the northern edge Eurasia: the Arabian Peninsula, China, Egypt. Europe, Greece, India, Iraq, Israel, Somewhere above the center in Africa is Olduvai Gorge.
Credit/Permission:
NASA,
NASA: Image #EL-1996-00155,
1972 /
Public domain.
Download sites:
NASA: Image #EL-1996-00155,
Wikimedia Commons:
NASA: Image #EL-1996-00155.
Image link: Itself.
Local file: local link: earth_blue_marble.html.
File: Earth file:
earth_blue_marble.html.
Caption: North America
from Apollo 16,
1972
Apr16.
You can see the Baja California Peninsula (which is about 1250 km long), the Rocky Mountains, and, towards the top, Lake Superior and Lake Michigan.
Credit/Permission:
NASA,
NASA: Image #AS16-118-18873,
1972 /
Public domain.
Image link: Itself.
Caption: Las Vegas, Nevada.
North is to the upper left. The Las Vegas Wash pours into the leftmost corner of Lake Mead. The Highway 95 to the north-west is clear. Interstate 15 is probably the curve that streaks from the word Las Vegas up to the right and then more or less to the top middle. The University of Nevada, Las Vegas (UNLV) is probably off the picture south of the word Las Vegas.
The city looks like a grey mold spreading over the Mojave Desert.
Credit/Permission: NASA,
NASA: ISS EarthKam,
before or circa 2004 /
Public domain.
Image link: Itself.
Earth, the one and only.
All other planets are failed Earths.
There are mountains, valleys, and continents etc. due to geological processes that we will discuss, but the range from highest to lowest points is only about 20 km:
Caption: "NASA pan photo mosaic of the Himilayas with Makalu and Mount Everest. The photo mosaic uses photos ISS008-E-13302 TO 13307 taken 2004 Jan28 taken from the International Space Station (ISS), Expedition 8 and added to The Gateway to Astronaut Photography. From The Gateway to Astronaut Photography of Earth." (Slightly edited.)
The image looks south from over the Tibetan Plateau. Makalu (8462 m, the 5th highest peak) is somewhere on left; Mount Everest (8850 m) somewhere on the right.
Credit/Permission: NASA,
2004 /
Public domain.
Image link: Wikipedia.
See Mount Everest videos below/at link:
Caption: "A cross section cartoon of the Mariana Trench depicting main structures and features." (Slightly edited.)
Caption 2: "The Pacific plate is subducted beneath the Mariana Plate, creating the Mariana Trench, and (further on) the arc of the Mariana islands, as water trapped in the tectonic plate is released and explodes upward to form island volcanoes." (Slightly edited from Wikipedia: Mariana Trench.)
Credit/Permission: ©
D.M. Hussong & P. Fryer, (1981),
Vanessa Ezekowitz (AKA User:Vanessaezekowitz),
2009 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Cross section of mariana trench.svg.
Local file: local link: mariana_trench.html.
File: Earth geology file:
mariana_trench.html.
Additionally, the Earth (not counting the atmosphere for the moment) is slightly oblate (Cox-240) due to the centrifugal force. For further explication, see the figure below (local link / general link: earth_oblate_spheroid.html)
Caption: "The equatorial (a), polar (b), and mean Earth radii as defined in the 1984 World Geodetic System revision." (Somewhat edited.) These Earth radii roughly specify the figure of the Earth.
The image shows the Western Hemisphere and the Americas---somewhat stylized.
Features:
Hydrostatic equilibrium on a large enough scale. On a small enough scale, there is the shape change due to the tides which are very noticeable on the human scale on the coasts of the oceans. For more on the tides, see Mechanics file: tide_earth.html.
Note, Earth's gravitational field g_average = 9.80665 N/kg (which is defined in some way) and Earth's gravitational field g_fiducial = 9.8 N/kg (as used by many including yours truly).
Note, in a strict sense, free fall means an object is moving only under the force of gravity, except for smallish non-gravitational perturbations.
Near-Earth astronomical objects are principally the Moon, Earth-orbiting artificial satellites, space debris, and near Earth objects (NEOs) (asteroids and comets) on close flybys of Earth.
The Earth's modulations from sphericity are small as discussed above.
So basically the Earth is a sphere.
In any large scale images, differences from a sphere are unnoticeable.
Gravity has pulled it into this shape.
Answer 3 is right.
An ideal fluid CANNOT resist a shearing force; it can only resist COMPRESSION. The Earth is NOT an ideal fluid, but under the weight of its own mass it acts approximately like a fluid in bulk.
The combination of self-gravity and pressure force results in the nearly spherical shape.
The solid and liquid pressure holds up the Earth's atmosphere too. The atmosphere is internally held up by its own gas pressure, of course.
Chemical bond forces of the rock and metals, the tidal forces of the Moon and Sun, and the centrifugal force provide only a bit of modulation from sphericity.
A fuller explanation of why sufficiently massive dense astro-bodies become approximately spherical is given in the figure below (local link / general link: hydrostatic_equilibrium_sphere.html).
Image 1 Caption: A diagram of spherically symmetric sphere of fluid in hydrostatic equilibrium which in this context means all fluid parcels are at rest (relative to an inertial frame).
Features:
For hydrostatic equilibrium (i.e., balance of forces), we find that
p_out*A = mg + p_in*A p_out = (m/A)g + p_in p_out = ρg*dr + p_in (dp/dr) = -ρg ,where dr is the thickness of the layer and ρ is the layer density and (dp/dr) is the pressure gradient---which is negative meaning that pressure decreases going outward. Note, the pressure outward at any spherical shell must support all the mass above the spherical shell, and so pressure increase going inward.
Actually, one has should prove that the hydrostatic equilibrium spherically symmetric sphere is stable: i.e., that vanishingly small perturbations damp out and do NOT cause progressive change to some other structure. We do prove this below actually.
Why?
Fluids have very low resistance to shearing forces. The ideal limit of an inviscid fluid (one that has NO viscosity: which is the resistance to shearing forces) has NO resistance at all. But, in fact, as we discuss below, some resistance to shearing forces are needed to make an arbitrary initial clump of fluid relax to a state of hydrostatic equilibrium.
A pair of shearing forces are parallel, but do NOT act along the same line. Thus, they can cause layers of a body to slide relative to each other.
In the case of any initial clump of fluid acted on by self-gravity and pressure acting in combination as shearing forces, fluid parcels will keep moving around until they CANNOT anymore---which is when the clump has relaxed to the self-consistent solution---where there are NO shearing forces acting and NO kinetic energy---which solution is just the hydrostatic equilibrium sphere.
Note, kinetic energy is always being lost due to viscosity (which is the resistance to shearing forces as noted above) which eventually dissipates all the kinetic energy into waste heat.
In astrophysical contexts, the waste heat will usually be radiated away as electromagnetic radiation (EMR).
The fact that self-gravity, pressure, and viscosity always move the clump toward hydrostatic equilibrium sphere proves that that structure is stable. Any perturbation is damped out by the aforesaid self-gravity, pressure, and viscosity.
Note, without some viscosity, there is NO way to dissipate kinetic energy and the clump of fluid will slosh around perpetually and NEVER reach hydrostatic equilibrium.
What if the clump of fluid initially had some angular momentum? This angular momentum will be conserved and the clump will relax to ideally to a uniformly rotating hydrostatic equilibrium oblate spheroid where only the self-gravity, pressure, and centrifugal force are acting. Note, there will also be rotational kinetic energy in the final state in this case.
In the astrophysical realm, the astro-bodies virtually always start formation with some angular momentum, and so virtually always at all stages in existence have some kind of average rotation, unless some process removes all angular momentum, but this virtually NEVER happens.
Only the pressure force is strong enough to resist sufficiently strong self-gravity. Atoms strongly resist being compressed.
But note the pressure force does NOT resist shearing forces.
So when the pressure force and gravity balance on every small bit of matter flow will essentially stop just described in general above.
Then one has spherically symmetric sphere self-consistent solution.
Well this depends on chemical composition, heat energy content, and rotation.
However, observations suggest the empirical rule that the size scale for a rocky astro-body must be >∼ 600 km and for a water ice astro-body must be >∼ 300 km (see Wikipedia: Dwarf planet: Hydrostatic equilibrium).
Yes. General relativity (GR) predicts a sufficiently dense massive object will collapse to being black hole with a ring singularity due to rotation (i.e., a Kerr black hole) or a point singularity if there is NO rotation (i.e., a Schwarzschild black hole). The singularities have finite mass and zero volume, and so have infinite density.
However, most people believe that true singularities are avoided by quantum gravity, but we have NO established quantum gravity theory, and so NO established theory of what happens deep in black holes.
The centrifugal force effect on Earth is relatively small.
It is much larger for Jupiter and Saturn which are distinctly oblate in some images.
See the false-color image of Saturn showing its oblateness in the figure below (local link / general link: saturn_oblate.html).
Caption: "In 2009 January and March, astronomers using NASA's Hubble Space Telescope (HST) took advantage of a rare opportunity to record Saturn when its rings were edge-on inclination, resulting in a unique movie featuring the nearly symmetrical light show at both of the gas giant planet's poles. It takes Saturn 29.4571 years to orbit the Sun, with the opportunity to image both of its poles occurring only twice during that time. The light shows are the Saturnian aurorae which are produced when electrically charged particles race along the magnetic field lines of the Saturnian magnetosphere and into the upper Saturnian atmosphere where they excite atmospheric gases, causing them to glow. Saturnian aurorae resemble the same phenomena that take place near the Earth's polar regions: i.e., the aurora." (Somewhat edited.)
Features:
The quantified oblateness is defined by the formula
where a is equatorial radius and b is polar radius.
Loosely speaking, quantified oblateness is the fractional squashing.
We can determine the mass of the Earth from the gravitation law and Newton's 2nd law (i.e., F=ma). For the calculation, see the figure below. (local link / general link: earth_mass.html).
Caption: Determining the Earth's mass.
The accepted value for the Earth's mass is Earth mass M_⊕ = 5.9722(6)*10**24 kg = 3.0033*10**(-6) M_☉.
Note we have used the astronomical symbols the Earth symbol ⊕ and the Sun symbol ☉ to label the masses for the Earth and Sun.
For the calculation to be independent of astronomical object masses, the gravitational constant G = 6.67430(15)*10**(-11) (MKS units) must be determined in the laboratory. This has been done though NOT to as a high an accuracy/precision as other fundamental physical constants (see NIST: Fundamental Physical Constants). In fact, the first reasonably accurate measurement was the Cavendish experiment (1798, G_obtained = 6.74*10**(-11) MKS units) which is pretty good for 1798.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Local file: local link: earth_mass.html.
File: Earth file:
earth_mass.html.
We can calculate the Earth's mean density---which is a very, very cruel density---a shown in the figure below.
Caption: Determining the Earth's mean density.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
The mean density of 5.5148 g/cm**3 (Cox-240) is partially set by matter under strong compression in the deep interior.
From modeling, the uncompressed density of the Earth is estimated to be 4.2 g/cm**3 (Se-418). This is the density the Earth material would have if it were uncompressed.
The modeling involves the ingredients we discuss in the next section The Interior of the Earth: How We Know About It.
The deepest drilling has only gone a few kilometers down---which is just scratching the surface on a planet with a mean radius of 6371.0 km. (see Wikipedia: Earth).
This understanding has had to be inferred from indirect evidence: density, primordial solar nebula composition, seismology, heat flow from the interior, mantle rock obducted into continental crust at convergent boundaries (AKA subduction zones) (see Wikipedia: Earth's mantle: Composition), other evidences (too numerous to mention), and modeling.
Let's detail the ingredients needed to understand the Earth's interior structure:
The Earth's mean density is 5.5148 g/cm**3 (Cox-240). But the density of the surface material (mainly silicates) is of order 2.5--3 g/cm**3 (Cox-257).
Thus, there must be interior material that is denser (when uncompressed) or of compressed material. In fact, both conjectures are true: there is material denser when uncompressed, but it is also compressed to high density by weight of the overlying material.
The intrinsically denser materials that made up the newly formed hot and molten Earth sank and the intrinsically less dense materials rose and all this was due to the buoyancy effect.
This process is called chemical differentiation---which we discuss in IAL 10: Solar System Formation: Chemical Differentiation.
The buoyancy effect and "chemical differentiation" is illustrated in the figure below (local link / general link: buoyancy_cylinder.html).
Caption: A graduated cylinder containing 6 liquids, four of which seem to be somewhat immiscible: maple syrup is at the bottom and olive oil is a the top.
The "chemical differentiation" is due to the buoyancy effect---placed in a fluid, objects rise/sink/float neutrally if the are less/more/equally dense as the fluid.
The tendency of some of the liquids in graduated cylinder to dissolve into each other prevents 6 clean layers from forming in the "chemical differentiation".
Credit/Permission: ©
User:Kelvinsong,
2013
(uploaded to Wikipedia
by User:,
2008) /
Creative Commons
CC BY-SA 3.0.
Image link: Wikimedia Commons:
File:Artsy density column.png.
Local file: local link: buoyancy_cylinder.html.
File: Fluids file:
buoyancy_cylinder.html.
The Earth formed out of the primordial solar nebula whose composition is known from the solar photosphere composition and primitive meteorites.
This composition is believed to have been fairly uniform throughout the solar system before chemical differentiation and other processes caused composition variations to arise.
We know that the volatiles are depleted on Earth because they were never strongly condensed and/or escaped from the early hot Earth.
But what of the elements that stayed on Earth and chemically differentiated?
For example, consider the most abundant dense refractory element iron (Fe):
The solar composition is, however, much more important than the Solar System because it is also approximately the cosmic composition (meaning inside modern galaxies: fiducial values by mass fraction: 0.73 H, 0.25 He-4, ∼ 0.02 metals) (i.e., the composition of the observable universe) for reasons explained below.
Features:
The horizontal axis is a normal linear axis in atomic number.
The vertical axis is a logarthmic axis in elemental mass fraction.
Many solar composition plots are by number fraction.
But Z is also the symbol for metalliticity (which we describe below).
Context must decide which meaning applies as usual.
It is obtained from observations of the solar photosphere and from primitive meteorites: i.e., meteorites that seem to have undergone little chemical processing since the solar system formation.
The primordial solar nebula composition is a key datum in modeling the formation and evolution of the Solar System since it is part of the initial conditions from which all else followed.
Assuming it came from well mixed interstellar medium (ISM), the solar nebula had a homogeneous composition.
Metallicity (with symbol Z) is net abundance of astro-jargon metals which are usually just called metals.
Metals are NOT to be confused with ordinarily-defined metals though some metals are metals.
The leading solar composition metals in decreasing order by number fraction are: oxygen (O), carbon (C), neon (Ne), nitrogen (N), magnesium (Mg), silicon (Si), iron (Fe), and sulfur (S) (Cox-28--29).
Why is this so?
To foray into cosmichemical evolution:
Lithium has also been affected by creation and destruction in stellar nucleosynthesis and supernovae since the Big Bang, but how much is uncertain which is the cosmological lithium problem.
Note that in the deep interior (i.e., the core) of the Sun and other stars is richer in He than solar composition because of ongoing hydrogen burning in the core.
Note also that white dwarf stars can be nearly all helium or metals in the interior due to post-main-sequence evolution.
Thus, the relative composition of the metals (including lithium) is approximately universal: i.e., the cosmic composition (meaning inside modern galaxies: fiducial values by mass fraction: 0.73 H, 0.25 He-4, ∼ 0.02 metals) of metals.
Note kilonovae may produce most of the R-process elements which are about half of all elements heavier than iron (Fe, Z=26). Kilonovae are the ejecta from neutron star mergers that have inspiraled due to loss of kinetic energy by gravitational waves. Most of the material from the 2 neutron stars ends up in a newly formed black hole or, sometimes, a larger newly formed neutron star.
The first stars the Population III stars had zero metals (aside from a little primordial lithium which goes without saying hereafter), but they are believed to have all been very large stars (because of formation with zero metals), and so exploded as supernovae within a few megayears and polluted the interstellar medium (ISM) with metals.
The next early generations of stars (which formed from the polluted ISM) had varying low metallicity: i.e., the Population II stars. So they have the cosmic composition (meaning inside modern galaxies: fiducial values by mass fraction: 0.73 H, 0.25 He-4, ∼ 0.02 metals), but with low metallicity.
The long-lived low stellar mass Population II stars are still around and show very low metallicity going down to Z ∼ 10**(-6) (e.g., Caffau's star (AKA SDSS J102915+172927)) which is 10**4 times smaller than Solar System metallicity Z ∼ 2.
Why the saturation?
Galaxies are NOT closed boxes. There are always outflows to and inflows from the intergalactic medium (IGM) The outflow remove ISM enriched in metals and the inflows inject IGM which has mostly just the primordial cosmic composition (fiducial values by mass fraction: 0.75 H, 0.25 He-4, 0.001 D, 0.0001 He-3, 10**(-9) Li-7)).
For a discussion of the saturation process, see file metallicity_evolution.html
Table: Gross Solar and Primordial Cosmic Compositions by Mass Fraction ___________________________________________________________________________ Substance Traditional G-1998 A-2009 Primordial Solar Solar Solar Cosmic Fiducial Fiducial ___________________________________________________________________________ H 0.73 0.7120 0.7154 0.75 He 0.25 0.2701 0.2703 0.25 Z 0.02 0.0180 0.0142 10**(-3) (counting D, He-3, and Li-7 as a metals) 10**(-9) (counting Li-7 only as a metal) ___________________________________________________________________________Notes:
Credit/Permission: ©
David Jeffery,
2006 / Own work.
Image link: Itself.
Local file: local link: solar_composition.html.
File: Solar System file:
solar_composition.html.
Caption: Satan, as imagined by Gustave Dore (1832-1883), in John Milton's (1608--1674) Paradise Lost (1674):
---Cardinal Wolsey (c.1473--1530) Act III, Scene 3 (scroll down ∼ 80 %) in Henry VIII (1613?), William Shakespeare (1564--1616).
By studying the propagation of seismic waves from earthquakes plus modeling (i.e., by seismology), the interior structure of the Earth (including temperature, pressure, phase of matter) can be inferred.
The phase information is particularly interesting: the seismic wave study allows us to see where the interior is solid and where it is liquid.
See Seismic waves and earthquake videos below (local link / general link: seismic_wave_videos.html):
Seismic waves and earthquake videos
(i.e., Seismic wave
and earthquake
videos):
We can measure heat flow and temperature directly at the surface and to some depth (Wikipedia: Geothermal gradient).
All kinds of other bits of evidence is used.
Among other things, the surface of the Earth is a boundary condition for the interior and it gives many constaints on interior conditions.
We have already noted some constraints: e.g., crustal composition.
One has to construct computer models of the Earth that match the observations discussed in the subsection above.
Solving for the interior structure of the Earth is, in fact, an inverse problem where one must obtain the model parameters from the observational data. But it's NOT a simple inverse problem where one puts the data values into formulae and calculates the model parameters. It's one where you assume model parameters and calculate predictions and compare those to actual observations. Usually, an iteration is needed to bring the predictions into agreement with the observations.
Of course, the model parameters obtained are fits to the observations and are only meaningful to the degree that the model is an adequate simplified representation of the interior structure. If it's NOT an adequate representation, then the model parameters may NOT mean much.
Among other conditions imposed on the Earth model, the model must have hydrostatic equilibrium: i.e., the pressure at every radius must be able to hold up the mass of all above that radius from collapse under the Earth's self-gravity.
These layers are shown in the figure below.
Caption: A cartoon of the interior structure of the Earth (HI-118; Ze2002-160).
My cartoon is from before or circa 2010 and is slightly dated.
An analysis from 2013, suggests that sulfur (S) is probably NOT a main component of the Earth's core (see Lidunka Vocadlo, 2013, Earth science: Core composition revealed, Nature).
It is now thought that oxygen (O) and silicon (Si) are the main components after iron (Fe) (approximately 80 % by mass) and nickel (Ni) (approximately 10 % by mass)
The liquid outer core may be about 10 % by mass O and Si and the solid inner core maybe about 3 % by mass O and Si.
Why were the lighter elements NOT excluded from the Earth's core by chemical differentiation?
Chemical differentiation isn't a perfect process. Some chemical chemical bonding may always keep some elements stuck together to some degree depending on the situation.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
The inner core is hotter than the outer core, but is a solid because the higher pressures near the center favor the solid phase.
Solid-state physicists can measure or calculate melting temperatures under high pressure.
The temperature and density profiles of the Earth can be calculated too. See the two figures below (unlinked; local link / general link: earth_density_distribution.html).
Caption: A cartoon of the Earth's interior temperature profile from modeling (Se-431).
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Caption: "Earth's radial density distribution (or profile) according to the Preliminary reference Earth model (PREM)." (Slightly edited.)
Features:
Caption: The Earth crust composition (elemental composition) by mass fraction shown in a pie chart.
Features:
So the values given in the pie chart and tables below are good representative values, but NOT timeless truth.
Note, the values in the pie chart and the first table don't agree with each other exactly.
Table: Earth Crust Elemental Composition by Mass Fraction Ordered by Abundance:
For the primordial solar nebula composition see file solar_composition.html.
It is in the form of chemical compounds of which there are a vast number mostly in form of crystals.
Most of this matter is also classifiable as rock and most of the rock is silicate (a kind of silicon compound) containing oxygen. That this so is very plausible based on the table above where oxygen and silicon are shown as the most abundant elements and they certainly are NOT in pure form in the Earth's crust. Silicate is often virtually a synonym for rock.
Note some rock is NOT in form of crystals, but in the form of amorphous solids.
Table: Earth Crust Chemical Compound Composition by Mass Fraction Ordered by Abundance:
The solid inner core and liquid outer core are probably mainly iron, but significant nickel (Ni), oxygen (O), and silicon (Si) are also present as discussed above.
There is also a second layering classification: lithosphere and asthenosphere:
Form groups of 2 or 3---NOT more---and tackle Homework 11 problems 2--10 on the Earth's structure.
Discuss each problem and come to a group answer.
Let's work for 5 or so minutes.
See Solutions 11.
The winners get chocolates.
Ah Brussels---Belgian chocolate, waffles, Belgian beer---the Germans know nothing about making beer---cafes, Brussels lace, le Sablon, le Musee royau de Beaux-Arts, (avec the Fall of Icarus), Pieter Bruegel the Elder (c. 1525--1569), comics, and Belgian comics---you've heard of Tintin---and my old pal Guy.
Credit/Permission: ©
Chmouel Boudjnah (AKA User:Chmouel),
before or circa 2005
(uploaded to Wikipedia
by User:Neutrality,
2005) /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Chocolate fountain.jpg.
Local file: local link: chocolate_fountain.html.
File: Art_c file:
chocolate_fountain.html.
The atmospheric temperature, most??? of the oceanic temperature, and the very thin uppermost continental ground temperature are determined by electromagnetic radiation (EMR) from the Sun (which becomes heat energy) and the greenhouse effect---which we discuss below in the section The Greenhouse Effect.
The electromagnetic radiation (EMR) flux above the atmosphere impinging on the Earth is on average 1367.6 W/m**2 (see NASA Earth fact sheet).
Answer 1 is right, but as we saw in
IAL 8: The Sun, the
solar constant
does vary.
The solar constant is defined to be the flux at the mean orbital radius of the Earth, and so does NOT have variation due to the eccentricity of the Earth's orbit. That variation is quite large, but averages out over a year.
But once the very short-time variations (due to sunspots mainly???) have been smoothed away the solar cycle variations are only of order 0.1 %.
Of course, very long term variations exist. Over centuries and over gigayears. Recall the Sun is has probably brightened by 30 % since 4.6 Gyr ago will probably brighten by 30 % more in the next 3.5 Gyr (WB-106).
The solar constant flux is captured by the Earth's circular cross-sectional area of pi*R**2 where R is the Earth's radius (Wikipedia: Sphere).
But to get the average energy flux at the top of the atmosphere, one must spread the captured power over the whole spherical surface area of 4*π*R**2 (Wikipedia: Sphere).
So the average flux at the top of the atmosphere is
solar constant * π*R**2 1367.6 W/m**2 * π*R**2 1367.6 W/m**2
------------------------- = ---------------------- = ------------- ≅ 340 W/m**2 ,
4*π*R**2 4*π*R**2 4
4π*R**2 is the surface area of the Earth.
About 30 % of this average flux is reflected by ground and Earth's atmosphere. See Earth's energy budget explicated in the figure below (local link / general link: earth_energy_budget_2.html).
So the heating of the Earth's surface AND the Earth's atmosphere is done by ∼ 240 W/m**2 of absorbed flux.
About 170 W/m**2 is absorbed by the Earth surface. This is an average value, of course. There is nothing at night and daytime absorption is very variable and depends on weather, latitude, topography, and other lesser features.
Solar power is the biggest of all renewable energy sources, and so eventually, I think, it must be the main energy source of the future---but when that future will arrive is very uncertain---20 years, 100 years?
The is no build up of heat energy on Earth: if there was temperature would increase forever.
We'll discuss how Earth's temperature is set below in the section The Greenhouse Effect.
What of other heat flows to the Earth surface?
The mean heat flow to the surface from the hot interior of the Earth is only about 0.08 W/m**2 (see Wikipedia: Earth's energy budget).
The tidal heating is 0.0059 W/m**2 (see Wikipedia: Earth's energy budget).
Answer 2 is right.
Clearly, geothermal heating is NOT what keeps us warm.
The geothermal energy going to the continents and continental shelves is primarily due to radioactive materials in the crust itself. The outflow is about 0.057 W/m**2???.
In the oceanic basins, the heat flux is about 0.099 W/m**2 and comes from the deep interior???.
I can't find the reference for these numbers at the moment, but I must have got them from somewhere once upon a time.
What is the deep internal source of heat?
Some of it is residual heat energy from formation (∼ 50 %) and some is from radioactive decay past and present of radioactive isotopes (∼ 50 %) (see Wikipedia: Earth's internal heat budget).
The combined internal heat energy drives primordial-radiogenic heat geology (see also Wikipedia: Earth's internal heat budget: Radiogenic heat: Primordial heat).
Further explication is given in the figure below (local link / general link: radiogenic_heat.html).
Caption: A graph of the estimated radiogenic heat fluxes to the Earth's surface from its interior long-lived radioactive isotopes.
Yours truly thinks the graph is just showing the instantaneous radiogenic heat fluxes and does NOT account for the delay time for the heat energy to propagate to the surface. But the original caption does NOT specify what exactly the curves are.
Features:
A radioactive nucleus may decay now or in gigayear. There is no way in principle to tell.
However the average decay rate is well defined: it is an exponential decay:
For relatively large samples, the exponential decay law is virtually exact.
The more commonly known one is the half-life, the time for the number of radioactive nuclei to decay by one half.
The relationship between half-life and e-folding time is derived as follows:
(1/2)N_0 = N_0*exp(-t_h/t_e) (1/2) = exp(-t_h/t_e) ln(1/2) = -t_h/t_e ln(2) = t_h/t_e t_h = t_e*ln(2) t_e = t_h/ln(2)where ln(2) = 0.6931 ... is the natural logarithm of 2 (see Wikipedia: Natural logarithm of 2).
These radioactive isotopes were created before the formation of the Solar System in supernovae which ejected them into the interstellar medium (ISM) whence they got into the solar nebula.
The primordial abundances of the radioactive isotopes in the Earth and throughout the Solar System are primarily known from the study of primitive meteorites.
It's curious to think that if nature had given us a significantly lower abundance of uranium-235, we would NEVER have had nuclear power, nuclear weapons, and, for better or worse, balance of terror.
The heat energy from the past is still in the Earth's interior because the rate of heat energy flux by heat conduction and convection is just very low for large rocky bodies.
To give a comparison number, the worldwide commercial energy consumption is ∼ 18 TW = 18*10**12 W circa 2018.
Since we can only project harvesting a tiny fraction of the total heat energy flow to the surface, it's clear that geothermal power will NEVER be a major source of commercial power though it be locally important sometimes.
For another comparison, let's do a Fermi problem. The basal metabolic rate (BMR) for a human is ∼ 100 W. This is just the power needed to exist, NOT doing anything.
There are of order 10**10 humans, and so the total power needed by humans to just veg is 1 TW.
It drives uplift that keeps the continents from eroding away and leaving Earth a water world.
Also volcanic outgassing provides carbon dioxide (CO_2) to the Earth's atmosphere over geological time. The CO_2 sink of calcium carbonate (CaCO_3) formation removes it from the Earth's atmosphere over geological time. So without volcanic outgassing photosynthesis and biota, at least on land would gradually turn off.
So despite the dangers of earthquakes and volcanoes, having an active primordial-radiogenic heat geology (see also Wikipedia: Earth's internal heat budget: Radiogenic heat: Primordial heat) is necessary to the biosphere as we know it.
The radiant flux absorbed by the Earth's atmosphere and Earth is on average 240 W/m**2. The part that is absorbed by the ground and ocean is 170 W/m**2 (see Wikipedia: Earth's energy budget).
These heat fluxes are much larger than the Earth's geothermal heat flux.
So solar irradiance powers the biosphere and keeps it warm.
Praise the Sun.
However, the smaller the rocky body or rocky-icy body, the faster heat conduction releases the heat energy to outer space and this lowers its power to drive primordial-radiogenic heat geology.
The resulting situation is as follows. The Earth and Venus have significant primordial-radiogenic heat geology. Mars has less, but some. Smaller rocky bodies or rocky-icy bodies (e.g., the Moon, Mercury, and the asteroids) have virtually none.
So such short-lived radioactive isotopes probably did drive primordial-radiogenic heat geology for awhile in the early Solar System, but they all decayed away and do NOT drive primordial-radiogenic heat geology now.
Why is that past heat energy from formation and past radioactive decay still there inside the Earth?
It just takes a very long time for heat energy to leak out from the interior of a massive object.
Why does size matter? The explication is given in the figure below.
Caption: Cooling time scale for rocky spherical bodies in the solar system.
Features:
The calculation ignores many complicated effects (e.g., real structure and differences in composition), but it it gives the right scaling of the effect of size on cooling.
The amount of residual/radioactive heat energy that a rocky body has is important for its geological activity since the heat flow of this energy is a major geological driver.
Note, there are two aspects:
Caption: A relative size comparison of the four rocky planets Mercury, Venus, Earth, and Mars and the rocky dwarf planet Ceres (which is also the largest asteroid).
The Venus image is false color and shows topography with the veil of Venusian atmosphere stripped away.
Unfortunately, the image of Venus of what the colors mean except that they show structure. The bright elongated horizontal region at the center is Aphrodite Terra which is one of the three Venusian terrae which are continent-like highlands.
The Mercury image is rather old since it cowlick of unimaged surface which has since been imaged by the NASA MESSENGER probe (MESSENGER Team Releases First Global Map of Mercury, 2009dec15).
The Moon should be shown too since it also counts as a large rocky body. Its radius is 0.271 Earth radii which is NOT so much smaller than Mercury's radius of 0.3829 Earth radii.
Credit/Permission: NASA,
2009
(uploaded to Wikipedia
by User:Weirdoinventor,
2009) /
Public domain.
Image link: Wikipedia:
File:5 Terrestrial planets size comparison.png.
Below we explicate primordial-radiogenic heat geology of some Solar System objects:
And apparently, its primordial-radiogenic heat geology is somewhat less than that of Earth. It's surface is renewed more often than once per gigayear, but this is about 5 times slower than the renewal time for most of the Earth's surface (CW-34).
Mars probably had primordial-radiogenic heat geology comparable to Earth's once. Now it is much slower, but probably NOT dead as older textbooks used to say.
Volcanic activity probably still occurs at a slow rate (HI-189; Baker, V. R. 2005, Nature, 434, 280).
They still have radioactive isotopes releasing heat energy, but it heat conduction to the surface releases it to the surface so quickly that it CANNOT drive primordial-radiogenic heat geology.
But they are all smaller than the Moon and long ago lost nearly all their residual heat energy.
Like the Moon and Mercury, they still have radioactive isotopes releasing heat energy, but it heat conduction to the surface releases it to the surface so quickly that it CANNOT drive primordial-radiogenic heat geology.
As mentioned above, aluminum-26 (half-life 0.717 Myr) may have driven the primordial-radiogenic heat geology even on rapidly cooling small rocky bodies like asteroids.
The asteroids are now nearly geologically dead, except for impact geology, space weathering, and diurnal temperature cycle weathering. All very slow processes.
Earth's large size has maintained its primordial-radiogenic heat geology.
This is important for life on Earth. As dangerous as volcanoes and earthquakes are, we need primordial-radiogenic heat geology.
If primordial-radiogenic heat geology turned off, Earth's continents would erode and wash away leaving us with an ocean planet or WATER WORLD, but without Kevin Costner (1955--).
Also volcanic outgassing sustains the carbon dioxide (CO_2) over geological time scales. Without CO_2 gas in the atmosphere, life as we know it would cease.
Then we'd have an ocean planet, unless the water all disappeared first.
The idea of continenal drift (a key component of plate tectonics) was introduced in the early 20th century by Alfred Wegener (1880--1930) and only slowly gained traction.
The full theory of plate tectonics only emerged in the 1960s through the work of many including Canadian John Tuzo Wilson (1908--1993).
In one sense, it is surprising that it was so late since it is the biggest of Earth's geological processes.
But the fact is that the motions of plate tectonics are excruciatingly slow on the human lifetime time scale---as most geological processes are---and the tectonic plates themselves are pretty thoroughly camouflaged.
So plate tectonics is NOT at all obvious.
Nowadays plate tectonics is a very robust theory. It's truth.
Of course, endless refinements continue to appear---and many of those have uncertain status: very strongly supported, possible, probably wrong, etc.
Here we can only give a simplified outline of plate tectonics.
To start with heat energy flows from hot to cold spontaneously which is a manifestation of the 2nd law of thermodynamics.
The temperature of the interior of the Earth rises going inward up to maybe 5000 K in the center.
Thus, heat flows outward in the Earth.
Some of the flow is by heat conduction: one atom's thermal kinetic energy being directly transferred to another or by FREE MOVING ELECTRONS in conductors.
This is why metal spoons are NOT good for stirring boiling water.
Answer 1 is right.
Material that is plastic can convect though very slowly compared to liquids. A plastic in this sense is a material that deforms permanently under an applied force (Wikipedia: Plasticity).
Actually, the combination of the Earth's rotation and the convection in the liquid iron outer core causes electric currents that drive a dynamo effect that creates the Earth's magnetic field. We discussed this briefly in IAL 8: The Sun. Somehow macroscopic kinetic energy gets turned into charge separation energy and then electrical currents flow which in turn generate magnetic fields.
As a recapitulation on convection, see the figure below (local link / general link: convection.html).
The heat absorption can be by heat conduction, radiative transfer, smaller scale convection, or some combination the 3 aforesaid heat transfer processes.
Buoyancy is actually a fluid pressure effect. It is familiar from playing in the pool.
The gravity on the expanded blob stays constant, but the pressure force increases with size. So there is a net force upward and the blob will accelerate upward.
In practice, a fluid layer is stable/unstable if its temperature gradient is sufficiently unsteep/steep.
Note, convection can only happen when the macroscopic parts of layer can move relative to each other. Therefore convection only happens in fluids: gases, liquids, and solids of sufficient plasticity---e.g., the Earth's mantle in plate tectonics.
The possibly broken-up, cooled blob loses buoyancy and sinks back to the hot lower surface.
The cycle though generally chaotic in detail is often rough approximate closed loop called a convection cell???.
Often one uses some approximate method of calculation of convection: e.g., the well-known mixing-length theory.
In the asthenosphere (i.e., the lower mantle), it is also believed that the plastic mantle convects and the convection cycle drives plate tectonics.
It is thought there are huge if slowly cycling convection cells in mantle convection---the time scale of a complete cycle thought to be ∼ 200 Myr (see Wikipedia: Mantle convection: Speed of convection).
See the cartoon of mantle convection and mantle convection videos in the figure below (local link / general link: usgs_004_convection.html) and the computer simulation of mantle convection in the second figure below (local link / general link: mantle_convection_model.html).
Caption: Convection in the asthenosphere driving plate tectonics.
This cartoon shows "whole" mantle convection which is favored circa 2017 (see Wikipedia: Mantle convection: Types of convection).
The alternative theory is "layered" mantle convection in which there are multiple vertical convection cells.
A "whole" mantle convection convection convection cycle is thought to take ∼ 200 Myr (see Wikipedia: Mantle convection: Speed of convection)
For further explication, see Plate tectonics videos below (local link / general link: plate_tectonics_videos.html):
Caption: "This figure shows a computer simulation for thermal convection (i.e., mantle convection) in the Earth's crust (5--10 km oceanic crust; 30--50 km continental crust), average thinkness 2886 km, ∼ 84 % of the Earth's volume. Colors closer to red are hot areas and colors closer to blue are cold areas. In this figure, a hot, less-dense lower boundary layer sends plumes (mantle plumes?) of hot material upwards, and likewise, cold material from the top moves downwards." (Somewhat edited.)
Features:
The surface manifestation of the asthenosphere convection cells are the tectonic plates which consist of two main regions: oceanic basins and relatively high continents.
The surface manifestations of the boundaries between asthenosphere convection cells are the tectonic plate boundaries There are three kinds as illustrated in the figure below (local link / general link: usgs_002_plate_boundaries.html).
Caption: A cartoon of illustrating tectonic plate boundaries: divergent boundaries, convergent boundaries (AKA subduction zones), and transform boundaries.
Very hot lava flows up from the deep asthenosphere and fairly quiescently (SWT-571) creates new crust in a relatively narrow valley called a rift.
But volcanoes are possible too as in Iceland (which straddles a divergent boundary) demonstrates.
The rifts are typically bounded by twin ridges.
Most divergent boundaries are under the oceans and are marked by giant mountain chain systems split by central rifts. These systems are called mid-ocean ridges.
Basalts to have small crystals and be dark (SWT-568).
As the material moves away from the mid-ocean rift (being dragged by the motion of the underlying asthenosphere convection cell), it cools and grows more dense and at a convergent boundaries (i.e., subduction zones) it can slides under another plate.
At oceanic convergent boundaries there is usually a deep oceanic trench.
A famous example of a convergent boundaries is the Mariana Trench in the western Pacific Ocean dropping to 10.984 km below mean sea level: the deepest place on Earth (Wikipedia: Mariana Trench). See the diagram of the Mariana Trench in the figure below (local link / general link: mariana_trench.html).
Caption: "A cross section cartoon of the Mariana Trench depicting main structures and features." (Slightly edited.)
Caption 2: "The Pacific plate is subducted beneath the Mariana Plate, creating the Mariana Trench, and (further on) the arc of the Mariana islands, as water trapped in the tectonic plate is released and explodes upward to form island volcanoes." (Slightly edited from Wikipedia: Mariana Trench.)
Credit/Permission: ©
D.M. Hussong & P. Fryer, (1981),
Vanessa Ezekowitz (AKA User:Vanessaezekowitz),
2009 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Cross section of mariana trench.svg.
Local file: local link: mariana_trench.html.
File: Earth geology file:
mariana_trench.html.
Between continental tectonic plates there are no trenches (SWT-594).
On subduction some subducting matter heats up from contact with the asthenosphere and then becomes low density molten rock that rises and emerges as lava that forms volcanoes SWT-594).
Volcanic mountain chains often form where a oceanic plate subducts below an oceanic or continental plate: e.g., the Andes of South America and the Cascades of Washington State (SWT-594).
Caption: Zagros Mountains from space.
They straddle the Iran-Iraq border.
They are a fold mountain systems.
There is no perfect folding, of course. But you can mountains are stretched in one direction. Those mountains are the upfolds.
Credit/Permission: NASA,
1992
(uploaded to Wikipedia
by User:Amizzoni~commonswiki,
2006) /
Public domain.
Image link: Wikipedia:
File:Zagros 1992.jpg.
There are also FAULT-BLOCK MOUNTAINS that occur when the crust is fractured and one side is uplifted. The Sierra Nevada Mountains in California are FAULT-BLOCK MOUNTAINS (SWT-607).
Granites tend to have large crystals from slow cooling of lava or magma (CW-195). They tend to be lighter in color ???? than basalts and less dense.
The continental material rose up above the oceanic crust because of its lower density---which is NOT full explanation of why continents form. (We discuss continents a little bit further below in the section The Past and Future of Plate Tectonics.)
Note, both continental and oceanic crusts are immensely complex with all kinds of variations: the distinction into basaltic and granitic just gives the main trend.
For example, the North American Plate and the Pacific Plate have a transform boundary in California: the San Andreas Fault. Earthquakes near transform boundaries are common (SWT-595).
In simple terms, the tectonic plates try to slide past each other, but are caught on each other by friction and other forces??? and elastic potential energy builds up until there is a sudden release of stored potential energy as kinetic energy.
Everything moves and shakes and then the transform boundary comes into a new relatively stable configuration---for awhile.
The tectonic plate boundaries, particularly on dry land, are NOT always obvious since surface material can camouflage them.
Of course, before modern geology, they were NOT recognized at all as tectonic plate boundaries.
The tectonic plate boundaries do move around over geollgical time scale: hence continental drift. Tectonic plates grow, shrink, and move.
The tectonic plates and tectonic plate boundaries have been mapped probably pretty completely and accurately.
There are 7 or 8 (depending on how you count them) major plates and 15 minor plates (i.e., tectonic plates of area less than 20 million km**2, but more 1 million km**2).
Caption: Map of the Earth's tectonic plates.
See Wikipedia: List of tectonic plates for all tectonic plates: minor plates, and microplates.
There are 15 tectonic plates shown on the map which include the 7 or 8 (depending on how you count them) 10 minor plates.
The major tectonic plates: African Plate, /Antarctic Plate, Eurasian Plate, Indo-Australian Plate (Australian Plate, Indian Plate), North American Plate, Pacific Plate, South American Plate.
For further explication, see Plate tectonics videos below (local link / general link: plate_tectonics_videos.html):
But there are a few number that cross land for part of their length.
For example, the Mid-Atlantic Ridge (a divergent boundary) crosses Iceland. See the figure below.
Caption: Iceland straddling
tectonic plate boundary,
a divergent boundary
the Mid-Atlantic Ridge.
In fact, the Mid-Atlantic Ridge crosses the Reykjanes Peninsula where Reykjavik is.
Circa 2023 on, the Sundhnukur eruptions (2023--) are disrupting life on the Reykjanes Peninsula---but if you choose to live on a divergent boundary ...
Credit/Permission:
U.S. Geological Survey (USGS),
before or circa 2005 /
Public domain.
Download site:
USGS: Understanding plate motions.
Image link: Itself.
The figure below (local link / general link: iceland_satellite_image.html) shows a satellite image of Iceland. There is NO obvious tectonic plate boundary visible even though the Mid-Atlantic Ridge goes right over Iceland.
Caption: A satellite image of Iceland covered mostly by snow and ice.
Mid-Atlantic Ridge goes right over Iceland and there are present lots of volcanoes and glaciers. But at least the untrained human eye CANNOT detect these features as such.
Note Iceland does NOT have an ice sheet. Only Antarctica and Greenland do in the Holocene (∼ 11650 BP--present). We are seeing glaciers, but also just mostly continuous snow and ice. For Iceland's largest glaciers, see Wikipedia: List of glaciers in Iceland: Largest glaciers by surface area.
Credit/Permission: NASA,
before or circa 2005 /
Public domain.
Download site: NASA: Visible Earth
Alas, a dead link.
Image link: Itself.
Local file: local link: iceland_satellite_image.html.
File: Earth file:
iceland_satellite_image.html.
Caption: "Rock outcrop in Iceland, a visible surface feature of the Mid-Atlantic Ridge, the easternmost edge of the North American plate. A popular destination for tourists in Iceland."
You wouldn't know this is part of a tectonic plate boundary without other geological evidence. It could be any old rock outcrop.
Credit/Permission: User:Pmarshal,
2006 /
Public domain.
Image link: Wikipedia:
File:Iceland mid atlantic ridge.JPG.
There are frequent volcanic eruptions in Iceland
along the Mid-Atlantic Ridge.
See the two figures below.
Caption: Krafla volcano in 1984.
Krafla is on the Mid-Atlantic Ridge as it crosses Iceland.
Credit/Permission: Michael Ryan,
U.S. Geological Survey (USGS),
1984
(uploaded to Wikipedia
by User:Peko,
2006) /
Public domain.
Image link: Wikipedia:
File:Krafla usgs.jpg.
Caption: "Lava flow during a rift eruption at Krafla volcano, northern Iceland, 1984."
Krafla is on the Mid-Atlantic Ridge as it crosses Iceland.
See also the eruption image at USGS Krafl site.
Credit/Permission: Michael Ryan,
U.S. Geological Survey (USGS)
1984
(uploaded to Wikipedia
by User:Galar71,
2007) /
Public domain.
Image link: Wikipedia:
File:Lava flow at Krafla, 1984.jpg.
See Volcano videos below (local link / general link: volcano_videos.html):
Volcano videos
(i.e., Volcano
videos:
Caption: San Andreas Fault, a transform boundary between the tectonic plates the North American Plate and the Pacific Plate which are both major plates. North of the San Andreas Fault is the convergent boundary (AKA subduction zone) between the North American Plate and the microplate the Juan de Fuca Plate.
The San Andreas Fault is one of the relatively few places where a tectonic plate boundary crosses land. The much of the coast of Southern California and Baja California is sliding northwest and will become an island in maybe of order 20 Myr (see Wikipedia: San Andreas Fault: Plate boundaries).
For more information on the San Andreas Fault, see USGS The San Andreas Fault site
Credit/Permission:
U.S. Geological Survey (USGS),
before or circa 2005 /
Public domain.
Download site:
U.S. Geological Survey (USGS).
Image link: Itself.
File: Earth: geology: plate tectonics file:
usgs_007_san_andreas.html.
But from the air, its linear form can be picked out. See the two figures below.
Caption: San Andreas Fault.
This is an aerial view of the San Andreas Fault splitting Carrizo Plain in the Temblor Range east of San Luis Obispo, California.
The San Andreas Fault is one of the relatively few places where a tectonic plate boundary crosses land. Lower California is will one day become an island.
For more information on the San Andreas Fault, see USGS The San Andreas Fault site
Credit/Permission: USGS.
circa or before 2005 /
Public domain.
Download site:
USGS:
photographer Robert E. Wallace, USGS.
Image link: Itself.
Caption: "San Andreas Fault in the Carrizo Plain, aerial view from 8500 feet altitude'' (November 2007nov16).
Double-click to see the high-resolution version.
From the air, the San Andreas Fault is a striking geological feature---a sort of long double ridge with a narrow valley between the ridges.
But on the ground, it may just be landscape as far as the geologically challenged can see.
The tectonic plates are jammed together and erosion has probably mostly covered the surface fault---but miles down it reaches.
Credit/Permission: ©
Ian Kluft AKA User:Ikluft,
2007 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Kluft-photo-Carrizo-Plain-Nov-2007-Img 0327.jpg.
Form groups of 2 or 3---NOT more---and tackle Homework 11 problems 11--17 on plate tectonics.
Discuss each problem and come to a group answer.
Oh, 5--10 minutes.
See Solutions 11.
The winners get chocolates.
Credit/Permission: ©
User:4028mdk09,
2009 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Becher Kakao mit Sahnehäubchen.JPG.
Local file: local link: chocolate_hot.html.
File: Art_c file:
chocolate_hot.html.
We can make some general remarks to start with.
The oldest oceanic crust is of order 200 Myr (see Wikipedia: Oceanic crust: Life cycle). Recall, the oceanic crust is directly formed and destroyed by mantle convection whose convection cycle is of order 200 Myr (see Wikipedia: Mantle convection: Planform and vigour of convection).
On the other hand, continental crust is NOT directly formed by mantle convection (see section Continent Creation below) and has a range of ages: estimates are 20 % before 3 Gyr Before Present (BP), 60 % between 3 and 2.5 Gyr BP, and 20 % between 2.5 BP and today (see Wikipedia: Continental crust: Origin).
Note, the oldest Earth rock known is zircon crystals from Western Australia that is dated to 4.4 Gyr (Wikipedia: Oldest dated rocks: Oldest terrestrial material).
We know that ocean basin crust is created at divergent boundaries.
How is the continental crust created?
The continents were created by two uplifting processes: accretionary wedges and volcanism:
Caption: An accretionary wedge at a subduction zone.
Continents are built up by accretionary wedges and volcanism.
Credit/Permission:
United States Geological Survey (USGS),
USGS Earthquake glossary,
before or circa 2009
(uploaded to Wikipedia
by User:Miya,
2009) /
Public domain.
Image link: Wikipedia:
File:USGS Visual Glossary-Accretionary wedge.gif.
Both sedimentary rock from accretionary wedges (granitic rock) and rock from volcanoes that go into making the continents are less dense than oceanic sedimentary rock and deeper rock???.
Thus, at convergent boundaries, where continental and oceanic tectonic plates meet the continents tend to be the winners---they tend to stay on top???.
So continents tend NOT be subducted and recycled in the giant mills of mantle convection.
The subduction rate of the continents is thus much slower than that of the ocean basin crust.
This is why continents are generally older than ocean basin crust and why parts of continents can be very old.
Of course, continents do erode as well as get built and so their surfaces CANNOT last forever. Their bits get washed in the ocean basins.
But it does seem that the total land area of the continents has NOT changed radically in the last 225 Myr or so despite the continents being shifted around a lot (see below).
So continent creation by accretionary wedges and volcanism and destruction by erosion (and maybe sometimes when continental tectonic plates meet at convergent boundaries by subduction) must be roughly in balance????. But the creation and destruction rates are both slower than for ocean basin crust, and so the continents on average are much older than the ocean basin crust.
UNDER CONSTRUCTION see the figure below (local link / general link: .html)
Caption: A cartoon of the origin of plate tectonics
UNDER CONSTRUCTION
Credit/Permission: ©
Nature (journal),
2024 / No permission.
Image link: Michael Marshall,
2024 Aug14, Nature, 632, 8025.
Image website: Michael Marshall,
2024 Aug14, Nature, 632, 8025.
Placeholder image:
alien_click_to_see_image.html.
Local file: local link: plate_tectonics_origin.html.
File: Earth: geology: plate tectonics file:
plate_tectonics_origin.html.
The early past of the tectonic plates gigayears ago is hard to trace.
Their motion, often called for historical reasons continenal drift, is uncertain.
It is NOT really possible I think to trace where the continents were to such early times as 3 Gyr ago. But some parts of the modern continents were around then.
The constant crustal creation and subduction has moved the continents around too much to trace their locations back to 3 Gyr.
It has been possible to trace the continents back to 220 Myr ago (i.e., 220 million years ago) using radioactive dating and magnetic dating with some certainty (CW-41).
Movements back to 600 Myr ago are known roughly (WB-91).
Caption: A replica of the fossil of the dromaeosauridae Sinornithosaurus (specimen NGMC 91, nicknamed Dave) at the American Museum of Natural History in New York City. Specimen NGMC 91 is about 75 cm long.
Sinornithosaurus was a small feathered dinosaur.
Some Sinornithosaurus types may have been able to glide (see Wikipedia: Sinornithosaurus: Feathers).
Sinornithosaurus is NOT in the lineage of birds---the dinosaurs of our day.
Credit/Permission: ©
User:Dinoguy2,
before or circa 2006 /
CC BY-SA 1.0.
Image link: Wikimedia Commons:
File:Sinornithosaurus Dave NGMC91.jpg.
Image 1 Caption: Continenal drift since 250 Myr Before Present (BP).
Features:
For example, the Atlantic Ocean is widening at about 3 cm/yr (Ze2002-158).
Answer 2 is right.
Pointing out this factoid seems to be de rigueur when discussing plate tectonics: the textbooks all seem to mention it (PF-95).
What is in store for the future?
Plate tectonic modeling suggests that most of the continents will ram together again to create a new supercontinent in about 250 Myr (WB-92).
Is there any fundamental reason for the arrangements of continents and tectonic plates as we see them?
Probably NOT.
Initial conditions on the early Earth were probably set randomly and then evolved in a deterministic fashion, but over the gigayears the motion may be so super-sensitive to initial conditions that it may NOT be predictable in practice from the initial conditions.
)_(17539652653).jpg)
Form groups of 2 or 3---NOT more---and tackle Homework 11 problems 11--17 on plate tectonics.
Discuss each problem and come to a group answer.
Oh, 5--10 minutes.
See Solutions 11.
The winners get chocolates.
How now can we eat a chocolate Easter Bunny?
Credit/Permission:
Mary Cynthia Dickerson
(1866--1923,
The American Museum Journal, Vol. XVII, 1917
(Natural History (magazine)
(known then as The American Museum Journal until 2002?))
(uploaded to
Wikimedia Commons
by User:Fae,
2015) /
Public domain.
CC BY-SA 2.0.
Image link: Wikimedia Commons: File:The American Museum journal (c1900-(1918)).
Local file: local link: chocolate_easter_bunny.html.
File: Art_c file:
chocolate_easter_bunny.html.
There are many other geological processes---and a lengthy discussion is beyond our scope---but we should mention a few main ones in brief.
Weathering of rock, erosion, and sedimentary rock formation which I collectively call EROSION GEOLOGY.
There is also hotspot volcanism (which is a feature of primordial-radiogenic heat geology and impact geology (i.e., the cratering by impactors from space).
There are other geological processes that do not much affect Earth: tidal heating geology (which is very important Jupiter's moon Io) and space weathering (which probably only affects airless worlds).
Liquid water can dissolve rock or provide a solution of other chemicals that dissolve rock.
Solid water (ice) can cause FROST WEDGING: water freezing in crevices expands and fractures.
Glaciers as they move can also break up rock. See figure below (local link / general link: glacier_johns_hopkins.html).
Caption: Johns Hopkins Glacier ice calving, Glacier Bay, Alaska.
See Glacier videos below (local link / general link: glacier_videos.html):
Wind is a much weaker than water in weathering in general, but it is important particularly in arid areas like the American Southwest where water weathering is comparatively week.
Wind weathering is very important on Venus and Mars where there is no liquid water.
Martian glaciers exist and must cause some weathering. They are covered by Martian soil, and so NOT obvious in images.
Liquid water can easily move dissolved material and fine particles. Larger particles or pebbles can be rolled along. Floods can move large objects up to the size of boulders.
Glaciers can move small and large rock fragments and boulders too.
Wind is much less powerful, but it can blow dust and sand around. In arid regions this is an important process.
Water usually and wind probably on average move rock material downhill depositing it lower regions and ultimately on the oceanic seafloor.
Both answers seem right to me.
The Earth would become an ocean planet eventually---if the water lasted so long.
The Mississippi Delta was created by erosion followed by geological deposition.
See the Mississippi Delta in the figure below (local link / general link: mississippi_delta.html).
Caption: The Mississippi Delta, Louisana.
The Mississippi Delta is formed by the geological deposition alluvium (soil, etc.) from the Mississippi River.
The US Army Corps of Engineers and others spend much of the 20th century trying to straighten the channels in the Delta for flood control among other things. The result of straighter channels and other human activities is less geological deposition and the Delta is eroding away. The sediments that used to build up the Delta get deposited out in the deep Gulf of Mexico. By 2100, New Orleans could be submerged:
So now people are unstraightening the channels to increase geological deposition..
Credit/Permission:
NASA,
NASA: ISS EarthKam,
before or circa 2004) /
Public domain.
Image link: NASA: ISS EarthKam.
Local file: local link: mississippi_delta.html.
File: Earth geology file:
mississippi_delta.html.
Caption: The rock cycle of the Earth.
Credit/Permission: ©
David Jeffery,
2004 / Own work.
Image link: Itself.
But most sedimentary rock is mostly silicates (CW-199).
Answer 1 is right.
Common cementing agents are silica (SiO2), iron oxides, and calcium carbonate (CaCO_3) (SWT-577).
Calcium carbonate is particularly important.
This is a major process by which CO_2 is removed quasi-permanently from the atmosphere.
Only quasi-permanently since volcanic action can free CO_2 again by volcanic outgassing during lava flows.
Note, the process requires liquid water.
But it's much more important than 8 % suggets.
Sedimentary rock is the covering layer of ∼ 73 % of the continents (see Wikipedia: Sedimentary rock) and apparently even more of the ocean basins (SWT-576).
Most of North America is covered by a veneer of sedimentary rock a few kilometers thick. In many parts of the continental interior sedimentary rock is almost all you see.
This is a pretty common sight in the American west. A famous example is the Grand Canyon (Se-437). See the figure below.
Caption: A view of the Grand Canyon presumably.
There was no caption at the USGS Grand Canyon site.
Credit/Permission:
U.S. Geological Survey (USGS),
before or circa 2004 /
Public domain.
Image link: Itself.
Studying the layers of rock (i.e., the strata), particularly sedimentary rock, is stratigraphy.
Studying the strata is a main way to learn about geological and biological history.
But there are places where the tectonic plates ride over point-like hotspots in the asthenosphere.
At a hotspot, a volcano can arise that is then shifted away from the hotspot by tectonic plate motion and becomes extinct.
The theorized origin of the hotspots are mantle plumes of hot rock that arise from the boundary of the outer core and the mantle.
However, since circa 2013, mantle plumes seem to be becoming a consensus theory:
But "the plume deniers are fading," says retired geochemist Stanley Hart (c. 1935--). "The major forces are getting older, and none of the young guys are picking it up." Plume critics aren't writing peer-reviewed papers, he says, so "I don't argue with them anymore; it's a distraction." (Slightly edited.)
Most seamounts are volcanic seamounts.
Caption: A diagram illustrating hotspot geology driven by mantle plumes.
Features:
There are lots of hotspots and therefore mantle plumes. See the figure below.
Caption: Mantle plume locations suggested by Gillian R. Foulger, 2010, Plates vs Plumes: A Geological Controversy.
Credit/Permission:
Gillian R. Foulger,
2011 /
Public domain.
Image link: Wikimedia Commons:
File:CourtHotspots.png.
The most famous hotspot is the one that has created the Hawaiian Islands and Emperor Seamount Chain (SWT-571).
The figure below (local link / general link: hawaii_hotspot.html) shows images of the Hawaiian Islands and the Hawaii hotspot.
Another well known hotspot is the Yellowstone hotspot which creates a geologically active area in the vicinity of Yellowstone National Park under which the Yellowstone hotspot is centered---you know, Old Faithful, etc.
Image 1 Caption: A satellite image in true color of the Hawaiian Islands from the Terra satellite (1999--).
The Big Island is obvious. Oahu (with Honolulu with Pearl Harbor) is the 3rd island from the left.
Image 2 Caption: "A diagram showing the
Hawaii hotspot and the
inferred underlying mantle plume
in cross section."
(Slightly edited.)
The Hawaii hotspot is ∼ 500 km wide (see Wikipedia: Hawaii hotspot: Characteristics), and so extends well beyond the Big Island (size scale 60 km) which is where most of the active volcanism occurs.
The tallest Hawaiian volcano is Mauna Kea which is considered dormant, but it will probably erupt again (see Wikipedia: Mauna Kea: Future activity). Mauna Kea is in fact one of the world's best observing sites for astronomy (probably the best in the Northern Hemisphere) and is the location for the Mauna Kea Observatories.
See Hawaii hotspot keywords below/at link:
See Volcano videos below (local link / general link: volcano_videos.html):
Volcano videos
(i.e., Volcano
videos:
Now there are two kinds of geologic craters that are quite different and have to be distinguished: volcanic craters and impact craters. Volcanic craters are on top of volcanoes and result from primordial-radiogenic heat geology. Impact craters arise from space debris (meteoroids, asteroids, and comets) falling on Earth.
We will discuss impactor physics and the distinction between impact and volcano craters in IAL 12: The Moon and Mercury and the current impactor danger to the Earth in IAL 16: Asteroids, Meteoroids, and Target Earth.
Most rocky/icy bodies in the solar system are heavily impact cratered, but Earth is NOT even though it has been impacted at a similar rate.
The absence of obvious impact craters is because of two reasons.
Thus, impact geology has been comparatively unimportant Earth since the heavy bombardment: during the heavy bombardment, impact geology was important on Earth.
There are 190 confirmed Earth impact craters as of circa 2024 and other probable or possible ones (see Earth Impact Database).
But most of these craters are NOT obvious the way craters on the Moon are.
Erosion has degraded their appearance in many cases and in many cases they are pretty much buried by sediment.
There is a fairly obvious impact crater in Quebec. See the figure below. (local link / general link: crater_manicouagan.html).
Caption: The Manicouagan crater as imaged by Space Shuttle mission STS-9 (launch 1983 Nov28) using Space Shuttle Columbia.
Features:
The view is oblique and to the west.
The area of the Manicouagan crater is rugged and heavily timbered and is in the Canadian Shield.
The visible part is ∼ 72 km in diameter (see Wikipedia: Manicouagan Reservoir: Manicouagan impact crater).
The Manicouagan crater is the 6th largest confirmed impact crater on Earth.
The island formed by Manicouagan Reservoir is Rene-Levasseur Island.
Manicouagan Reservoir is drained at the south end by Manicouagan River which flows south ∼ 200 km and empties into the Saint Lawrence River not far from it becomes the Gulf of Saint Lawrence.
The impactor is believed to be an asteroid of ∼ 5 km in size scale.
Caption: A political map of Mexico.
The Chicxulub crater (which is an impact crater) straddles the northern coast of the Yucatan Penisula with center just east??? of Progreso, Yucatan. It is centered near the village of Chicxulub. Yours truly believes Chicxulub is pronounced chick-shoe-lube.
The Chicxulub crater is ∼ 150 km in diameter and is the 3rd largest impact crater known on Earth (see Wikipedia: List of impact craters on Earth: Largest craters (10 Ma or more)). But it is entirely covered by sedimentary rock???.
The Chicxulub crater was discovered by finding shock-exposed rock and subsequent geological investigation.
The Chicxulub impactor hit ∼ 66 million years ago and caused the mass extinction at the end of the Cretaceous period (i.e., the Cretaceous-Paleogene (K-Pg) extinction event) that included the extinction of the dinosaurs.
How? The Chicxulub impactor may have touched off worldwide fires (perhaps firestorms, but that is debated: see Cretaceous-Palaeogene firestorm debate) and caused dust in that atmosphere that a multi-year winter (Se-574).
Keywords for the map: Bay of Campeche, Belize, Caribbean Sea, Central America Chicxulub, Yucatan, Chicxulub impact crater, Chicxulub impactor, Clipperton Island (not on map), Costa Rica (not on map), Cuba, El Salvador, Guatmala, Honduras, Gulf of California (Sea of Cortez) Gulf of Mexico, Isla de la Juventud (Cuba), Mexico, Mexico City, Nicaragua, North America, Pacific Ocean, Panama (not on map), Progreso, Yucatan, United States of America (USA), Yucatan.
Caption: "This shaded relief image of Mexico's Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretaceous-Tertiary (K-T) extinction event, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life then on Earth."
You'd never know the Chicxulub crater was there without some authority to tell you.
Credit/Permission: NASA,
2000
(uploaded to Wikipedia by
User:David Fuchs
2010) /
Public domain.
Image link: Wikipedia:
File:Yucatan chix crater.jpg.
There are a few impact craters that look like impact craters.
The most famous is Meteor Crater (AKA Barringer Crater) near Winslow, Arizona. See the two figures below.
Caption:
Meteor Crater (AKA
Barringer Crater) east of
Winslow, Arizona, just
off I-40, Arizona.
Meteor Crater is about 50,000 years old, has a diameter of about 1.2 km, and is about 180 meters deep.
The Meteor Crater impactor was an iron-rich meteoroid of about 50 m in diameter. The impact energy was equivalent to about that of 20-megaton H-bomb (FK-362).
The Meteor Crater impactor itself was fragmented and spread about in the crater or ejected out. There is no single big meteorite to be found it seems.
Credit/Permission:
US Geological Survey (USGS),
before or circa 2005 /
Public domain.
Download site:
USGS:
MeteorCrater.
Image link: Itself.
Caption: Meteor Crater in Arizona.
More on Earth craters can be found at the Geological Survey of Canada's Earth Impact Database.
Credit//Permission: NASA,
before or circa 2005 /
Public domain.
Download site: NASA: Visible Earth.
Alas, a dead link.
Image link: Itself.
As aforesaid, small impact craters get erased pretty quickly. They can be just muddy holes in the ground like the Carancas impact event crater. The Carancas impactor hit near Carancas, Peru, 2007 Sep15. For images of the Carancas impact event crater, google Carancas crater.
See Asteroid videos impactors below (local link / general link: asteroid_impact_videos.html):
Form groups of 2 or 3---NOT more---and tackle Homework 11 problems 15--19 on plate tectonics and volcanism
Discuss each problem and come to a group answer.
Oh, 5--10 minutes.
See Solutions 11.
The winners get chocolates.
Did you know that cocoa may be the great brain food---see Daisy Yuhas, 2013, Is Cocoa the Brain Drug of the Future?---it makes mice smarter---but maybe only in unprocessed form---just when you thought it was safe to scarf.
More debunking of dark chocolate: The dark truth about chocolate: Nic Fleming, The Guardian, Sun 25 Mar 2018---candy, NOT health food.
Credit/Permission: ©
Simon A. Eugster (AKA User:LivingShadow),
2010 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Schokolade-schwarz.jpg.
Local file: local link: chocolate_swiss.html.
File: Art_c file:
chocolate_swiss.html.
The table below specifies this composition.
_________________________________________________________________________
Earth Atmosphere Composition
_________________________________________________________________________
Gas Percentage by Mass Percentage by Number
(%) (%)
_________________________________________________________________________
N_2 (nitrogen) 75.52 77.
O_2 (oxygen) 23.14 21.
Ar (argon) 1.29 0.99
CO_2 (carbon dioxide) 0.05 0.033
Ne (neon) 0.0013 0.0018
He (helium) 7*10**(-5) 5.2*10**(-4)
CH_4 (methane) 1*10**(-4) 1.5*10**(-4)
Kr (krypton) 3*10**(-4) 1.1*10**(-4)
H_2 (hydrogen) 5*10**(-5)
O_3 (ozone) 4*10**(-5)
N_2O (nitrous oxide) 3*10**(-5)
CO (carbon monoxide) 1*10**(-5)
NH_3 (ammonia) 1*10**(-6)
H_2O (water vapor) 0.06 to 1.7 0.1 to 2.8
(Not counted in the atmosphere composition above.)
_____________________________________________________________________________
References: Se-439,
CW-296, and
Cox-258
(but note Cox has the wrong exponents for some numbers).
____________________________________________________________________________
Now lets expand a bit on the components of the composition of the Earth's atmosphere.
But N_2 is necessary for life: it is used making in many organic compounds.
Both biological and non-biological methods of fixing nitrogen (i.e., converted to ammonia or nitrates) exist: see, e.g., Wikipedia: Nitrogen cycle.
The main respiration reaction is C_6H_12O_6 + 6O_2 = 6CO_2 + 6H_2O + released energy where C_6H_12O_6 is glucose which is a sugar.(Fundamentals of Geology).
Photosynthesis provides plants with energy and also substance---their mass largely comes from carbon from the air (Photosynthesis: Discovery). The latter point means that the most biomass that is NOT water (e.g., much of us) comes from carbon from the air via photosynthesis. Plants photosynthesize, animals eat plants, then animals eat animals---and that's the food chain for you.
The main photosynthesis reaction is 6CO_2 + 6H_2O + light energy = C_6H_12O_6 + 6O_2 where C_6H_12O_6 is glucose which is a sugar.(Fundamentals of Geology).
The Earth's carbon cycle is illustrated in the figure below (local link / general link: carbon_cycle.html).
Caption: "This carbon cycle diagram shows the storage and annual exchange of carbon (C) between the Earth's atmosphere, hydrosphere and geosphere in gigatons---or billions of tonnes---of carbon (C) (GtC). Combustion of fossil fuels by people adds about 5.5 GtC of carbon (C) per year to the atmosphere." (Slightly edited.)
Carbon (C) in plants mostly comes from the air---and animals get their carbon (C) from plants.
Features:
Most basically because salt sea water gets converted into fresh water on land through the hydrological cycle: i.e., evaporation from the sea and rain onto land.
Ozone absorbs ultraviolet light from the Sun that is dangerous to life.
For penetration of ultraviolet through the atmosphere, see the figure below.
Caption: "Levels of ozone (O_3) at various altitudes, and related blocking of several types of ultraviolet radiation. The ozone concentrations shown are very small, typically only a few molecules O_3 per million molecules of air. But these ozone molecules are vitally important to life because they absorb the biologically harmful ultraviolet radiation from the Sun. There are three different types of ultraviolet (UV) radiation, based on the wavelength of the radiation. These are referred to as UV-a, UV-b, and UV-c. The plot also shows how far into the atmosphere each of these three types of UV radiation penetrates. We see that UV-c (red) is entirely screened out by ozone around 35 km altitude. On the other hand, we see that most UV-a (blue) reaches the surface, but it is NOT as genetically damaging, so we don't worry about it too much. It is the UV-b (green) radiation that can cause sunburn and that can also cause genetic damage, resulting in things like skin cancer, if exposure to it is prolonged. Ozone screens out most UV-b, but some reaches the surface. Were the ozone layer to decrease, more UV-b radiation would reach the surface, causing increased genetic damage to living things." (Slightly edited.)
DU/km are Dobson units per km---these are rather obscure units related to ozone concentration.
Credit/Permission: NASA,
before or circa 2011
(uploaded to Wikipedia
by User:Hardwigg,
2011) /
Public domain.
Image link: Wikipedia:
File:Ozone altitude UV graph.svg.
Chlorofluorocarbons (CFCs) used in refrigeration and air condition escape into the atmosphere and destroy ozone (Se-440). They are being phased out.
Unfortunately, H_2 (molecular hydrogen) can also destroy ozone. If we convert to a hydrogen economy, then H_2 leakage may become a significant environmental problem. The issue has been debated intensely recently.
Caption: Earth's atmosphere structure: The US Standard Atmosphere (US, 1962) runs of density, pressure, sound speed, and Temperature with altitude (geometric altitude, NOT geopotential altitude). The zero-point for altitude is NOT sea level???, but 611 m below sea level to allow for dry land below sea level.
The US Standard Atmosphere is similar to the International Standard Atmosphere. Both are sort of global average models of the Earth's atmosphere.
The plot also shows the approximate altitudes for various objects.
Atmosphere Layers and Objects:
Credit/Permission: ©
User:Cmglee,
2011 /
CC BY-SA 3.0.
Local file: local link: atmosphere_structure.html.
Image link: Wikimedia Commons:
File:Comparison US standard atmosphere 1962.svg.
File: Earth atmosphere file:
atmosphere_structure.html.
Thus, the Earth's atmosphere has motion, both relatively steady and strongly vargying, and heat flow
The figure below (local link / general link: hadley_cell.html) explicates and illustrates the dynamic Earth atmosphere.
Caption: Atmospheric circulation of Earth's atmosphere displaying the Hadley cells, the Ferrell cells and the polar vortices.
Features:
The temperature difference between these two pairs of regions is sufficient for convective instability.
The convection keeps the temperature difference from being larger than it is.
Obviously, the atmospheric circulation has an average behavior, but small deviations can chaotically grow into relatively large deviations that we call weather.
It is the insulating effect of a planetary atmosphere that keeps the planet surface at a higher temperature than it would have if it simply re-emitted absorbed star flux like a single temperature radiator: i.e., a blackbody radiator.
The figure below (local link / general link: heat_flow.html) explicates the greenhouse effect by an everyday life analogy.
Caption: Heat flow illustrated for the steady state of a heated house with thermal insulation in cold winter conditions.
The more thermal insulation, the slower the heat flow.
In simplified equation form,
F = k(T_high - T_low) ,where k is thermal conductivity, T_high is the temperature of the system with the higher temperature, and T_low is the temperature of the system with the lower temperature (see Wikipedia: Thermal Conductivity: Equations).
Note that as thermal insulation ↑, k ↓, and thus F ↓.
Balanced means F_in = F_out.
The house in the image illustrates the system, where the furnace supplies F_in (which is fixed) and the outflow is to the outside.
Inside the system the temperature is T_in and outside the temperature T_out (which is fixed).
Since F_in = F_out, the system is in steady state and at a constant equilibrium temperature T_in.
This causes k ↓ and F_out = k(T_in - T_out) ↓.
Now F_in > F_out and T_in ↑.
But that makes F_out ↑.
Eventually, F_in = F_out again and balanced is restored---but at a higher T_in than before.
But in any case, the Earth's surface temperature can be made as high as you like. If k=0, the surface temperature would increase forever.
In this case, F_in fixes the temperature T uniquely as determined by the Stefan-Boltzmann law for blackbody radiation:
F_in = F_out = σ*T**4 ,where we have Stefan-Boltzmann constant σ = 5.670367(13)*10**(-8) W/*m**2*K**4). Thus,
T=sqrt(F_in/σ)uniquely.
Now if you add thermal insulation for the outflow (but NOT the inflow), you can increase T: i.e., k ↓ T ↑.
The Earth treated as a blackbody radiator gives a lower limit on the Earth's surface temperature. See below The Greenhouse Effect for more details on the Earth treated as a blackbody radiator.
The situation we are considering is when the planetary atmosphere is relatively transparent to electromagnetic radiation (EMR) from the parent star inflowing to the planet surface and relatively opaque to thermal radiation (which is probably rather close to being blackbody radiation) outflowing from the surface to space. The difference transparency to inflowing and outflowing electromagnetic radiation (EMR) is due to the difference of the wavelength band of the two EMR flows.
For example, for the Earth, the inflowing EMR is largely in the visible light band (fiducial range 0.4--0.7 μm) (to which the Earth's atmosphere is rather transparent) and the outflowing EMR is largely in the infrared band (fiducial range 0.7 μm -- 0.1 cm) (to which the Earth's atmosphere is rather opaque).
The relative opaqueness to thermal radiation from the planet surface is the thermal insulation.
It causes the surface temperature to rise in order to increase the emission rate of thermal radiation and establish a balance between inflow and outflow of EMR.
This increased temperature due to a planetary atmosphere is the greenhouse effect.
It keeps the average surface temperature of the Earth well above the chilly surface temperature that a blackbody-radiator Earth would have.
At present, humankind is increasing the atmospheric carbon dioxide (CO_2) (which is the greenhouse gas after water vapor which we have NO direct control over), and so increasing the greenhouse effect and the average Earth surface temperature. For the atmospheric carbon dioxide (CO_2) trends, see NOAA: Trends in Atmospheric Carbon Dioxide. For some more details, see Wikipedia: Keeling curve: Mauna Loa measurements.
The increasing average surface temperature could have disastrous effects for the biosphere and humankind.
Caption: Albedo (i.e., reflectance) as a percentage as a function of Earth land cover (i.e., surface type) and cloud type.
Note the Earth overall albedo (to be precise its Bond albedo which gives overall reflectance back to outer space of an astro-body) is α_b_⊕ = 0.306 (see Wikipedia: Bond albedo: Examples).
Features:
Albedo can be given in percentage form in which case it is the decimal fraction form times 100 %. This what the image uses.
In the analysis below, we use symbol α for albedo and the decimal fraction form---and NOT the percentage form.
If the body is approximately a blackbody radiator, the effective temperature is approximately the actual surface temperature, and so is a good characteristic or sort of average temperature. If the body is NOT approximately a blackbody radiator, the effective temperature is still often a useful value for characterizing the body particularly for comparison to other bodies.
The α_b is the Bond albedo which as aforesaid gives overall reflectance back to outer space of an astro-body. Therefore (1-α_b) gives the amount of EMR absorbed by an astro-body.
The Stefan-Boltzmann constant σ = 5.670367(13)*10**(-8) W/*m**2*K**4).
The formula agrees with the one given by Wikipedia: Effective temperature: Planet.
__________________________________________________________________________________________ Table: Effective Temperatures for the Inner-Solar-System Worlds __________________________________________________________________________________________ Planet R_orbital_mean α_b_r T_eff T_eff T_(mean/fiducial) (real) α_b=0 α_b_r (AU) (K) (K) (K) __________________________________________________________________________________________ Mercury 0.387098 0.068 447.4 439.5 100 (night), 700 (day) Venus 0.723332 0.90 327.3 184.0 740 Earth 1.000001018 0.306 278.3 254.0 288 Moon 1.000001018 0.136 278.3 268.3 100 (night), 390 (day) at equator Mars 1.523679 0.25 225.5 209.8 210 __________________________________________________________________________________________Note 1: The α_b_r values are the real Bond albedos of the specified inner Solar System objects (see Wikipedia: Bond albedo: Examples).
Note 2: Specified inner-Solar-System worlds: Mercury ☿, Venus ♀, Earth ⊕, Moon ☽, Mars ♂.
Venus has an extreme greenhouse effect and Earth a moderate one.
That depends on what other counterfactual assumptions you make?
For example, if you turn off the greenhouse effect for Venus, but keep its Bond albedo α_b_♀ = 0.90 (see Wikipedia: Bond albedo: Examples), then Venus will have a very low average temperature closely approximating the effective temperature 184.0 K given in the table above.
But Venus's greenhouse effect is caused by Venusian atmosphere which also gives Venus its high Bond albedo.
Without the Venusian atmosphere, Venus would probably have a Bond albedo similar to that of the Moon 0.136. Then Venus would have probably have an average temperature an average temperature closely approximating the effective temperature 327.3 K given in the table above.
Answer 1 is right essentially.
Penguins might prefer -19° C.
Currently, the worldwide average is 15° C (288 K) (see Wikipedia: Instrumental temperature record: Absolute temperatures v. anomalies).
It's the Goldilocks predicament---the greenhouse effect has to be just right---or at least it should stay mostly the way it has been through most of the Holocene (∼ 11,700 BP--present).
Note, before the Holocene (∼ 11,700 BP--present) was the Pleistocene (2,580,000--11,700 BP) and the two together are the Quaternary (2.580 Myr BP--present). The Pleistocene (2,580,000--11,650 BP) is also the fiducial end of the Last Glacial Period (115,000--11,700 BP) of the Quarternary glaciation (2.580 Myr BP--present) which is still going on. The Next Glacial Period (maybe 50,000---100,000 years AP = after present). So the continental ice sheets will return---but NOT soon enough to save us from global warming.
Beginning with Industrial Revolution (c.1760--c.1840), CO_2 in the atmosphere has been increasing.
The Industrial Revolution (c.1760--c.1840) is exemplified by the figure below.
Caption: An animation of the first kind of steam engine, the Newcomen engine (invented 1712).
The Newcomen engine has the essential ingredient of all heat engines: a hot reservoir (the fire), a cold reservoir (the ambient air), and a working substance (water both in liquid and steam form).
Heat engines turn heat energy into mechanical energy, but never with 100 % efficiency as dictated by 2nd law of thermodynamics.
From the primitive Newcomen engine sprang the glory and misery of the modern world.
Credit/Permission: User:Emoscopes,
2006 /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Newcomen atmospheric engine animation.gif.
See Industrial Revolution videos below:
In 1760, CO_2 abundance was about 280 ppm (parts per million in air) which is about what it had been for millennia (and all of historical human history until 1760) (James F. Kasting, 1997 or after, The Carbon Cycle, Climate, And The Long-Term Effects Of Fossil Fuel Burning, scroll down ∼ 25%).
Historical, CO_2 abundance values can be determined from air bubbles and other inclusions in ice cores drilled in Greenland, Antarctica, and other cold places.
See Ice core videos below/at link:
The figure below is what we find and what we predict for CO_2 abundance.
Intergovernmental Panel on Climate Change (IPCC)
CO_2 records and predictions.
Caption: The historical record back to 1000 CE is from ice core measurements.
Direct measurements have been done since about 1960 when abundance was 315 ppm. The last direct measurement on this plot was from 2000 when the abundance was about 370 ppm.
In various scenarios CO_2 abundance is seen to rise by varying amounts by 2100 The IPCC states that much of the variation is due to varying human response.
Actually many people think there is more uncertainty than the IPCC has found.
In 2011, CO_2 is/was about 390 ppm (Carbon dioxide in Earth's atmosphere) and since 1960 it has risen by about 22% (Wikipedia: Keeling curve). Probably by about 2015, the abundance will go above 400 ppm---which will be a bit of a psychological threshold.
Some people believe that anything above 350 ppm is dangerous---and we need to scrub the atmosphere.
In 2003, the increase was 3 ppm which is a record increase (Carbon Dioxide Reported at Record Levels). The recent average increase has been about 1.8 ppm
The increase amount does fluctuate, but it is plausible that the 2003 increase was caused by increased fossil fuel burning in Asia, particularly China and India.
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Synthesis Report, IPCC, SYR-Fig. 9-1a,
2001 /
IPCC
with correct credit.
Image link: Itself.
Keeling curves (carbon dioxide (CO_2) abundance versus time plot) showing the period 1958--present and the last 5 years are shown in the figure below (local link / general link: keeling_curve.html).
Image 1 Caption: The up-to-date Keeling curve (atmospheric carbon dioxide (CO_2) abundance versus time graph) since inception in 1958 circa Mar15 (Daniel C. Harris 2010, Anal. Chem. 2010, 82, 7865--7870, "Charles David Keeling and the Story of Atmospheric CO_2 Measurements", Fig. 2). from Mauna Loa Observatory, Mauna Loa, Hawaii Island (the Big Island), Hawaii.
Image 2 Caption: The same for the last 5 years.
The red curve is the monthly-average curve and the black curve is a running average curve (see detailed explanation below).
Features:
One can also say that the Keeling curve from Mauna Loa is one for an average location on Earth rather than an average of Keeling curves for many locations on Earth.
So it is a Earth average Keeling curve in special sense of the word average.
The bottom graph is the recent CO_2 measurements.
Prior to the beginning of the Industrial Revolution (c.1760--c.1840), the CO_2 abundance was ∼ 280 ppm. Since the about the beginning of the Holocene (∼ 11,700 BP--present) and the Neolithic (c.12,000--c.4000 BP, c.10,000--c.2000 BCE), the CO_2 has been in the range ∼ 260--280 ppm (see Wikipedia: Carbon dioxide in Earth's atmosphere: Concentrations in the geologic past).
The Northern Hemisphere seasons dominate the seasonal cycle because it has more land mass than the Southern Hemisphere (see Wikipedia: Carbon dioxide in Earth's atmosphere: Annual and regional fluctuations).
The running average curve will probably NOT fall below 400 ppm again for centuries.
The monthly-average curve did NOT fall below 400 ppm in 2016 September when it minimized: 401 ppm was the minimum. So probably both the monthly-average curve and the running average curve will NOT fall below 400 ppm again for centuries.
Since 2010, the slope has been ∼ 2.5 ppm/year.
If this linear growth continues, CO_2 will reach 450 ppm in ∼ year 2034.
International discussion often cites stabilization at 450 ppm as a goal. Climate modeling suggests that stabilization at 450 ppm will keep global warming at under or about 2° C over the ∼ year 1880 global average temperature which is also a discussed international goal (see Wikipedia: United Nations Framework Convention on Climate Change).
Yours truly finds it hard to believe we will stabilize at 450 ppm, but we might be able to delay it beyond 2034.
If the linear growth in CO_2 continues longer, CO_2 will reach 560 ppm (about twice the pre-industrial abundance of ∼ 280 ppm) in ∼ year 2078. It has been estimated that 560 ppm would lead to ∼ 3° C increase over year 1880.
It should be noted that climate modeling predictions have large uncertainties.
By the by, if CO_2 reaches 560 ppm, we all become werewolves---but don't let anyone know.
However, ∼13.3° is considered the fiducial global temperature for pre-industrial global temperature and is approximately the average global temperature for 1850--1900.
The Industrial Revolution (c.1760--c.1840) was earlier than 1850--1900, but the burning of fossil fuel had NOT yet started causing significant global warming by 1850--1900.
Using this rate and temperature anomaly 0.8°C for the year 2000, we find we reach temperature anomalies 1.5°C, 2°C, and 3°C in, respectively, years 2035, 2060, and 2110.
For the later years, the above results are very uncertain extrapolations. However, reaching temperature anomaly 1.5°C by ∼ 2035 seems very likely.
The Paris Agreement (2015) set temperature anomaly 1.5°C as the preferable upper limit on temperature anomaly. Alas, it seems this upper limit will be breached.
However, keeping the temperature anomaly less than 2°C may be achievable.
The greenhouse effect raises the average global temperature above these hypothetical chilly values ∼14.5°C (i.e., 13.3+1.25 from Image 3). So the greenhouse effect is good, in fact. But as global warming shows, you can have too much of a good thing.
There is no doubt that the CO_2 increase since the beginning of the Industrial Revolution (c.1760--c.1840) is primarily caused by the burning of fossil fuels (i.e., coal, oil, and natural gas).
When we burn these fuels, we release CO_2 where the carbon component has been locked up in the ground as organic fossil fuel for geologically long times: millions to hundreds of millions of years???.
Of course, CO_2 is always being released and absorbed from the atmosphere by a variety of processes which collectively form the Earth's carbon cycle:
SOURCES:
SINKS:
The combination of these sources and sinks is the Earth's carbon cycle which is illustrated in the figure below (local link / general link: carbon_cycle.html).
Caption: "This carbon cycle diagram shows the storage and annual exchange of carbon (C) between the Earth's atmosphere, hydrosphere and geosphere in gigatons---or billions of tonnes---of carbon (C) (GtC). Combustion of fossil fuels by people adds about 5.5 GtC of carbon (C) per year to the atmosphere." (Slightly edited.)
Carbon (C) in plants mostly comes from the air---and animals get their carbon (C) from plants.
Features:
Nevertheless, some fraction of the CO_2 we produce stays in the atmosphere for centuries: about 65 % according to some calculations (James F. Kasting, 1997 or after, The Carbon Cycle, Climate, And The Long-Term Effects Of Fossil Fuel Burning, scroll down ∼ 10%).
The SIMPLE prediction is that if you increase a greenhouse gas, you should increase the greenhouse effect and cause global warming. This prediciton was first made by Svante Arrhenius (1859--1927) in 1896.
But climate is NOT simple.
There are all kinds of complex FEEDBACK MECHANISMS and also other effects such as increasing dust pollution which can increase reflection of sunlight and cause GLOBAL COOLING.
Nevertheless, CLIMATE MODELING does predict that increased CO_2 combined with other effects will lead to global warming---but there are still great uncertainties.
In the 20th century---of fond memory---it seems that the GLOBAL MEAN temperature rose by 0.6 ± 0.2 K (see Wikipedia: Instrumental temperature record).
It is NOT easy to meaure GLOBAL MEAN temperature especially going back in time, and so that value may be more uncertain than indicated.
The GLOBAL MEAN temperature can be reconstructed from historical measurements and natural records like ice cores from ice caps in Greenland, etc. See figure below.
Caption: Annual global mean temperature relative to the mean 1961--1990 temperature.
The grey region on the lower plot indicates the range of uncertainty???. It is considerable, and so it is NOT certain that temperatures were generally cooler over the 2nd millennium.
The shape of this curve has been called the hockey stick.
Since the curve was first published in about 1999, there have been many other calculations with widely different results for the past millennium. They all pretty much agree, however, that the Earth after 1980 has been warmer than any time since 1000 AD (reporter, 2005, Science, February 11, 307, 828).
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Synthesis Report, IPCC, SYR-Fig. 2-3,
2001 /
IPCC
with correct credit.
Image link: Itself.
The GLOBAL MEAN temperature varition does NOT show, of course, the complex local temperature variation.
We must look at other data representations for that. See figure below.
Caption: Annual temperature trends all over the Earth for 1976 to 2000.
The dots indicate the increase in annual temperature per decade averaged over the period 1976--2000.
As one can see, temperature change has NOT been uniform, but has been rather complex. Some regions have even gotten colder.
Non-uniform change is probably what we can expect for the future.
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Synthesis Report, IPCC, Fig. 2-6b,
2001 /
IPCC
with correct credit.
Image link: Itself.
Is the temperature change of the 20th and early 21st centuries anthropogenic or just a natural fluctuation?
The Intergovernmental Panel on Climate Change (IPCC) has given their conclusion. See figure below.
Caption: A comparison of models with measured temperature.
The comparison shows models with natural, anthropogenic, and combined forcing for 1860--2000.
The grey region for the model results indicates the range of uncertainty in the model predictions.
An objection in the past to computer model climate predictions was that they could NOT fit the PAST, and so how could you believe them for the FUTURE.
Well now they can fit the PAST.
But how many free parameters have been used?
You can always fit any curve if you adjust the unknown controls (i.e., free parameters). I guess one could find out.
But in any case, it is significant evidence that global warming (AKA anthropogenic climate change) is occurring.
The evidence has firmed up since this figure was generated 5 or so years ago.
There is still lots of uncertainty though.
It seems every year or so, there's a wups moment when something is discovered NOT to have been modeled adequately.
But so far those wups moments have NOT changed the qualitative conclusions much.
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Synthesis Report, IPCC, SYR-Fig. 2-4,
2001 /
IPCC
with correct credit.
Image link: Itself.
What about the future of global surface temperature?
Circa 2022, the IPCC predicts temperature changes from Pre-industrial Era (before c.1760) when global surface temperature was ∼ 14°C due to doubling the carbon dioxide (CO_2) abundance from the Pre-industrial Era (before c.1760) ∼280 ppm to 560 ppm: transient climate response (TCR) 1°C to 2.5°C and equilibrium climate sensitivity (ECS) 2.5°C to 4.0°C with best estimate 3°C.
These predictions are based computer simulations and climate and paleoclimate data.
Note, there is still considerable uncertainty.
The IPCC does their best, but there are objectors to their predictions outside (and even inside) their ranks---but the objectors go both ways---from "why worry" to "apocalypse now".
See figure below for the range of predictions of GLOBAL MEAN temperature from a somewhat out-of-date modeling.
Caption: IPCC predictions for temperature increase.
The temperatures are relative to the 1990 global mean temperature.
Under various circumstances the mean global temperature is seen to rise by varying amounts in the next 100 years.
The IPCC states that much of the variation is due to varying human response.
Actually many people think there is more uncertainty than the IPCC has found.
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Synthesis Report, IPCC, SYR-Fig. 9-1b,
2001 /
IPCC
with correct credit.
Image link: Itself.
Climate is complex and subject to many natural processes which are NOT yet fully predictable.
If there is significant future global warming, what are some possible consequences?
But the overall biosphere is likely to be loser in that complex ecosystems might be devastated.
There already has been some significant sea level rise since 1880 and more is expected. See the two figures below (local link / general link: sea_level_rise.html; unlinked).
Caption: "Global sea level rise 1993--2014. Data from Neil White of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), originally obtained by satellites TOPEX/Poseidon, Jason-1, and Jason 2." (Somewhat edited.)
Features:
There must be an elaborate procedure for arriving at an average sea level.
But the rise rate is NOT expected to stay constant. So the 26 cm prediction is NOT robust.
Caption: IPCC predictions for the rise in mean sea level.
They present 6 models that depend on varying circumstances many of which are under human control. There also uncertainty envelopes.
Many people believe that the uncertainties are greater than the IPCC estimate.
Credit/Permission: ©
Intergovernmental Panel on Climate Change (IPCC),
from publication
Climate Change 2001 - Working Group I - The Scientific Basis, IPCC, WG1 TS Fig. 24 /
IPCC
with correct credit.
Image link: Itself.
Some low-lying island nations (and southern Florida) could suffer severely with the maximum sea level rise predicted in some scenarios. Naturally, these places are NOT happy about this prospect.
What should be done? This is a policy question.
This is usually a slow leaking process, but over millions or billions of years an atmosphere can be diminished.
The lightest particles have the highest speed, and so have the strongest tendency to escape. Note, the Earth doesn't have much molecular hydrogen gas or helium gas.
Earth rock contains volatile element atoms trapped in the rock. Small amounts compared to the rock/metal mass of the Earth, but enough to give us atmosphere and oceans.
These volatiles are continually released by volcanic activity: they tend to be released when the rock is melted and spewed on to the surface of the Earth.
This process is called volcanic outgassing.
This theory has had its ups and downs in acceptance.
At present, theory that comets from the Kuiper belt brought most water to Earth seems to be gaining ground.
See the figure below illustrating volcanic outgassing.
Caption: A cartoon of volcanic outgassing.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Local file: local link: volcanic_outgassing.html.
File: Earth file:
volcanic_outgassing.html.
But how did we get to the happy atmospheric state we enjoy now? Happiness being having a warm puppy---no, happiness is having liquid water.
The Goldilocks principle has helped us:
"Primordial Venus is too hot for liquid water."
"Primordial Mars (or Mars sooner rather than later) is too cold."
"But primordial Earth is just right."
And liquid water is all important for life as we know it and it exists only in a narrow temperature range and only if pressure is greater than about 0.01 atmospheres (i.e., 1 atmosphere is current Earth sea level atmospheric pressure which is about 10**5 Pascals.) See this water phase diagram.
See references Water health FAQ Frequently Asked Questions and Water for human beings
As you know some life has evolved to live outside of the ocean, but it maintains its own internal ocean.
Another reason for needing liquid water is get rid of the large CO_2 abundance and to prevent a runaway greenhouse effect (similar to what happened on Venus).
The early Earth needed more greenhouse effect than now since the Sun was about 30 % less bright 4.6 Gyr ago (WB-106).
So considerable atmospheric CO_2 was needed to keep Earth warm enough for life and liquid water.
The theoretical result that the Sun was about 30 % less bright 4.6 Gyr ago (WB-106) seems as sure as a purely theoretical result can be.
But maybe there is something we do NOT understand about the early Sun or the early.
Or maybe we don't understand the early Earth well enough.
The problem with making the theories consistent on this point is called the faint early Sun paradox.
This is what happened to Venus which has surface atmosphere pressure about 92 times that of Earth, an atmosphere that is 96.5 % CO_2 by (number???), and a mean surface temperature of 735 K (i.e, 462 C)---which as people always note is hot enough to melt lead (melting temperature 600.61 K at Earth surface pressure and probably a bit higher on Venus).
Caption: Dante & Virgil in Hell.
In the Divine Comedy first part the Inferno, Dante Alighieri (1265--1321) and the shade of Virgil (70--19 BCE) journey through the Nine circles of Hell.
Where among others, they find Ulysses:
With one ship
only, and with that little band
Which chose not to desert me; far as
Spain,
Far as Morocco, either
shore I scanned.
Sardinia's
isle I coasted, steering true,
And the isles
of which that water bathes the
strand.
I and my crew
were old and stiff of thew
When, at the narrow strait,
we could discern
The boundaries
Hercules set far in view
That none should dare beyond, or further learn.
Already I had Sevilla on the
right,
And on the larboard
Ceuta lay
astern.
Then we rejoiced; but soon to grief were brought,
A storm
came out of that strange land, and found
The ship,
and violently the forepart caught.
Three times it made her to spin round and round
With all the waves;
and, as Another chose,
The fourth time, heaved the stern up,
the prow drowned,
Till over us we heard the waters close.
Go ancient shade, we ask of thee no more.
The last quote is a free variation by yours truly.
After early times when a CO_2 atmosphere first built up, it seems that carbonate rock production has usually outpaced CO_2 volcanic outgassing.
CO_2, which was once a dominant atmospheric species, has dropped to being a trace species.
400 Myr ago, CO_2 abundance was still about 20 times what it is today (WB-62), but even that was only about 0.7 % by number of the atmosphere.
Now it is only about 0.033 % by number.
Anthropogenic release of CO_2 from fossil fuels created by ancient life CANNOT stop the return of the glaciers.
Caption: Johns Hopkins Glacier ice calving, Glacier Bay, Alaska.
See Glacier videos below (local link / general link: glacier_videos.html):
Credit/Permission: National Oceanic and Atmospheric Administration (NOAA), Image ID: corp1862, NOAA Corps Collection, Location: Alaska Southeast, Photographer: Commander John Bortniak, NOAA Corps Photo Date: 1991 August / Public domain.But over a millennium or two the CO_2 abundance would come back to about where it was before the Industrial Revolution (c.1760--c.1840), because the oceans tend to absorb it up to some saturation limit (Ka-60%).
So anthropogenic global warming is only a temporary problem. It's NOT going to save us from the next glacial period of the current ice age (i.e., Quarternary glaciation (2.580 Myr BP--present)) which started circa 2.58 Myr ago and isn't over as far as we know (WB-76).
We are just in an interglacial period which started circa 12,000 years ago and may well end in a few tens of thousand more (see Next Glacial Period (maybe 50,000---100,000 years AP = after present)).
For some details of the Quarternary glaciation (2.580 Myr BP--present), see the figure below (local link / general link: quarternary_glacial.html).
Caption: The last 450 kyr of the Quarternary glaciation (AKA the current ice age, 2.58 Myr--present) illustrated by runs of temperature anomaly (i.e., temperature relative to 15° C???) (blue curve), atmospheric CO_2 concentration (ppmv) (green), and dust concentration (red curve) determined from Vostock ice cores.
We will NOT discuss dust concentration in this figure.
Features:
Note temperature given with zero point set to a fiducial value rather than the standard temperature scale zero is called temperature anomaly.
During the glacial periods ice sheets covered extensive regions of the Northern Hemisphere, land and ocean.
The time periods of relatively high temperature are roughly the interglacials of the Quarternary glaciation.
Over the last 800 kyr, the glacial periods have been ∼ 100 kyr in length and the interglacials ∼ 10 kyr in length (see Wikipedia: Quarternary glaciation: Description).
We are currently in an interglacial called Holocene (∼ 11,700 BP--present).
However, the current hypothesis for the next glacial period, put succinctly, is the Next Glacial Period (maybe 50,000---100,000 years AP = after present).
The scale is too large to show the details of the post-1700 epoch where anthropogenic effects (mostly obviously anthropogenic CO_2 concentration increase and global warming) have become important.
However, there is a complex interaction of effects from the biosphere, geology, atmospheric composition (in particular the varying atmospheric CO_2 concentration), and the astronomical Milankovich cycles.
The Milankovich cycles are as follows:
None of the Milankovich cycles has constant rate of evolution due to astronomical perturbations (in particular gravitational perturbations).
Thus, they have NO exact periods.
The complex interaction of the Milankovich cycles among themselves and with the other causes of Quarternary glaciation results in the inexact periodicity of the glacial period-interglacials cycle of the Quarternary glaciation (2.580 Myr BP--present).
On a much longer time scale than that of the current ice age, the Sun is still brightening---as the figure below illustrates---and thus increasing the heating the Earth.
Caption: The plot shows the evolution of the Sun's luminosity, radius, and effective temperature with time. Thus, the illustrates key aspects of the Sun's life phases.
Features:
The plot is NOT quite consistent with the estimate, but exact consistency between different astro sources is hard to find. Calculations of the model quantities vary somewhat between sources. This is a consequence of uncertainties in the modeling.
About 3.5 Gyr from now, the Sun will probably be ∼ 30 % brighter than now.
The solar brightening is a pretty modest change for the Sun for next 5 Gyr or so.
The course of events which will doom life first is NOT certain. Various scenarios are possible.
However, liquid water will drastically diminish for many reasons and life might become extinct everywhere for that reason by ∼ 3 gigayears after the present (Wikipedia: Future of Earth: Loss of oceans). Life as we know it requires liquid water.
By the same time, steady release of carbon dioxide (CO_2) by volcanic outgassing might give the Earth a carbon dioxide (CO_2) atmosphere leading to a runaway greenhouse effect which will make the Earth too hot for liquid water in any case and which is what happened to Venus (Wikipedia: Runaway greenhouse effect: Venus).
But we don't have to worry about these melancholy stories since they occur on a time scale far longer than human history. We only contemplate them philosophically.
Another doomsday scenario---there are so many of them.
Where did the O_2 come from?
First, note that O_2 is a highly reactive gas and would relatively quickly disappear over megayears or hundreds of megayears if it weren't being continually produced (HI-125). It reacts to form oxides like rust (HI-125).
Our current oxygen-rich atmosphere could never be established from volcanic outgassing???.
Answer 3 is right.
Yes, plants gave rise to the condition that brought about .
Caption: The unhappy consequences for plants of photosynthesis. You know, herbivores are just plant predators.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
Local file: local link: plant_herbivore.html.
File: Biology file:
plant_herbivore.html.
Of course, rather inert N_2, NOT O_2, is the dominant species presently.
N_2 must have taken over as dominant species as CO_2 dropped due to carbon becoming locked in carbonate rock and also due to O_2 production from plants.
Water was produced by volcanic outgassing or a hard comet rain as noted above and mostly became our oceans.
What is the fate of water?
At present, up to about 12 km above sea level---the exact altitude varies with latitude---is the troposphere.
The troposphere is lower atmosphere in which our weather occurs (WB-138). The upper boundary of the troposphere is the tropopause. There is relatively little mixing of air through the tropopause.
At the top of the troposphere the temperature is about 208 K (WB-137) and water vapor that air can contain there is very tiny.
Most water will condense out and fall inside the troposphere.
Thus, convection cells in the troposphere can't carry water up to great altitudes above the troposphere.
But the order of one gigayear, the brightening of the Sun will cause the mean global surface temperature to reach about 70 degrees C (or 340 K) and then the troposphere will extend to over 100 km in altitude (WB-129,138) which means (although we omit the argument) that water vapor will be convected up to over 100 km in altitude????.
At those altitudes, UV radiation from the Sun is available to break H_2O into H and O.
A much greater fraction of H atoms will then escape the atmosphere by having escape velocity than they do now.
Caption: A cartoon of Earth losing its water in the future.
Credit/Permission: ©
David Jeffery,
2003 / Own work.
Image link: Itself.
The future conditions of the Earth after massive H_2O loss begins are hard to predict, but the oceans might be gone by 1.5 Gyr ???? (WB-142).
Some liquid water could remain due to the still-ongoing volcanic outgassing (WB-141). And so some primitive life could persist in ponds.
But sooner or later the Earth will get too hot for liquid water and life will end---at least life as we know it.
Perhaps some exotic evolution will preserve complex life---or hyper-intelligent beings of the future might transcend mere physical limitations.
When the liquid water gone or sufficiently gone, CO_2---which disappeared into calcium carbonate deposition mainly in liquid water---could make a comeback. Volcanic outgassing without competition from calcium carbonate deposition could give the Earth a rich CO_2 and then Earth would go the way of Venus.
Of course, the end of the Sun's main sequence life as discussed in IAL 9: The Life of the Sun spells the doom of the Earth anyway in 5 to 6 Gyr.
However, we briefly touch on
earliest history
of life on Earth
in the figure below
(local link: )
Local file: local link: .
see the figure below
(local link /
general link: earth_archean_eon.html).
Image 1 Caption: An artist's impression of Archean Eon (4.031--2.5 Gyr BP) on Earth.
We think that microbial life may first appeared on Earth 3.480 Gyr ago at least and perhaps 4.2 Gyr ago (Wikipedia: Earliest known life forms; Robert F. Service, 2014 Jul12, Science "Our last common ancestor lived 4.2 billion years ago" maybe; Wikipedia: Abiogenesis; Wikipedia: History of life on Earth; Wikipedia: History of life on Earth: Earliest history Earth). But we don't know how exactly it arose. But somehow:
Note the 4.2 Gyr value is NOT based on the fossil record, but on a statistical study of genomes that tries to identify and date the last univeral common ancestor (LUCA) of all life on Earth (Robert F. Service, 2014 Jul12, Science "Our last common ancestor lived 4.2 billion years ago" maybe). Well, except maybe viruses (Wikipedia: Last univeral common ancestor (LUCA)).
Features:
The presolar grains also determine the age of the Earth = 4.56730(16) Gyr BP.
The age of the presolar grains is determined by radioactive dating of primitive meteorites.
However, Image 1 does convey the correct qualitative impression. At ∼4 Gyr BP, Moon was probably of order 10 times closer than today, and so would have an angular diameter of order 10 times bigger than today: i.e., ∼5° (Wikipedia: Origin of the Moon: Formation). Tidal accelertation caused the Moon to slowly spiral away from the Earth. Currently, the Earth-Moon distance is increasing by 3.830(8) cm/yr (Wikipedia: Tidal acceleration: Quantitative description of the Earth-Moon case).
Note "stromatolites
are layered
sedimentary rock
formations
(microbialites)
that are created mainly by
photosynthetic
microorganism"
(Wikipedia: Stromatolites: slightly
edited).
Then there are 1970s rock bands . . .
But to conclude, the Earth is an evolving place.
Anatomically modern humankind have been around only since ∼ 200--300 kyr BP (see Wikipedia: Anatomically modern human; Wikipedia: Jebel Irhoud), but even that has seen two or three interglacials including the present one (see Wikipedia: Interglacial).
But the really big changes, we only contemplate philosophically. They are outside of the time scale of human society.
We breach the time barrier to the far past and far future---deep time---only by scientific inference.
Form groups of 2 or 3---NOT more---and tackle Homework 11 problems 25--30 on the greenhouse effect.
Discuss each problem and come to a group answer.
Oh, 5--10 minutes.
See Solutions 11.
The winners get chocolates.
Ah Brussels---Belgian chocolate, waffles, Belgian beer---the Germans know nothing about making beer---cafes, Brussels lace, le Sablon, le Musee royau de Beaux-Arts, (avec the Fall of Icarus), Pieter Bruegel the Elder (c. 1525--1569), comics, and Belgian comics---you've heard of Tintin---and my old pal Guy.
Credit/Permission: ©
Chmouel Boudjnah (AKA User:Chmouel),
before or circa 2005
(uploaded to Wikipedia
by User:Neutrality,
2005) /
Creative Commons
CC BY-SA 3.0.
Image link: Wikipedia:
File:Chocolate fountain.jpg.
Local file: local link: chocolate_fountain.html.
File: Art_c file:
chocolate_fountain.html.
