Caption: A cartoon of a common version of the giant impact hypothesis for the origin of the Moon (Se-457).

Features:

1. Some million years to about hundred million ears after the formation of the Earth and its chemically differentiation, a protoplanet impactor of order the size AND mass of Mars ♂ impacted the Earth ⊕ at an angle probably NOT 0°, 90°, or 180° to the Earth's direction of motion in space and probably NOT at zero impact parameter.

2. The oldest moon rocks brought back by the Apollo program are ∼ 4.5 Gyr old (see Wikipedia: Moon rock). This suggests the impact was ∼ 4.5 Gyr or earlier. So no later than of order 100 Myr after the formation of the Earth which is now given as occurring 4.54(5) Gyr ago (see Wikipedia: Age of the Earth).

3. The hypothetical impactor protoplanet is often called Theia after the mythological Theia (whose name just means goddess). The mythological Theia was Titaness mother of Selene, the Greek mythological Moon goddess.

4. The impactor was also chemically differentiated with an iron core and a silicate mantle.

5. There was deep impact of the impactor on the Earth and the cores of the Earth and impactor bounced initially and then merged.

   Essentially much of the impactor combined with Earth and significantly increased its size. It is possible that very dense materials like gold and platinum were spread in the Earth's crust by the impactor (SRJ-168). It has been wondered how these materials are abundant as they are in the Earth's crust.

6. Some mantle debris from both objects was thrown into space: it became ejecta.

7. Some of the ejecta fell back to Earth and some escaped Earth altogether.

   But some of the ejecta went into orbit and began to accrete under self-gravity to form the primordial Moon within a short period that is probably in the range from tens of days to 100 years (see Wikipedia: Giant impact hypothesis: Basic model of impact).

8. The heat energy of the ejecta caused it to outgas almost all of its volatiles leaving it volatile-depleted. This explains why Moon rocks are are volatile-depleted (HI-150).

9. The ejecta that formed the Moon was initially molten or very hot and also contained radioactive isotopes. Collectively, the heat energy was sufficient to cause the early Moon to be molten and undergo chemically differentiation.

10. A hot iron core, mantle, and crust formed (see Wikipedia: Internal structure of the Moon).

11. The original lunar crust was heavily impacted by heavy bombardment during the 1st gigayear of the Solar System. It became the strongly cratered, light-colored lunar highlands

12. Some lunar impactors were very large and weakened the crust sooner or later allowing lava from the hot interior to flow out into the giant impact craters (i.e., giant lunar basins). The lava solidified into relatively dark-colored, giant lava plains which we call lunar maria.

    Most lunar maria probably formed more than 3 Gyr ago though some regions may be as young as 1.2 Gyr (see Wikipedia: Lunar maria: Ages).

13. The giant impact hypothesis has great advantages as a theory:

    1. It explains why Moon lacks volatiles and is low in iron compared to the Earth, but has a surface composition much like that of the Earth's mantle.

    2. Evidence from impact crater shows that large impacts were common in the early Solar System. In early Solar System overall theory of the early Solar System protoplanet with many leftover protoplanets still swarming around. So a giant protoplanet impactor is NOT improbable.

    3. Computer simulations show that giant impact hypothesis is physically quite possible. But, of course, they don't tell us exactly what the impactor was or how it hit. All we can do is create plausible scenarios and calculations that lead to what we find today: Earth and Moon.

14. See Moon formation and evolution videos below (local link / general link: moon_formation_evolution_videos.html).
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