Caption: "Earth's radial density distribution (or profile) according to the Preliminary reference Earth model (PREM)." (Slightly edited.)

Features:

1. The units of the vertical axis are gm/c**3 and the author is trying klutzily to show that you need to multipy by 10**3 to get the units in kg/m**3.

2. The density discontinuities are striking and biggest ones mark the solid-liquid phase transitions that occur at the inner core--outer core boundary and the outer core--mantle boundary.

3. Actually, the transitions at all the discontinuities must be rather complex when viewed on a smaller scale.

4. The ocean density is, of course, ∼ 1 g/cm**3: i.e., the density of water.

5. The Moho discontinuity is the discontinuity between the crust and mantle. Its eponym is Croatina seismologist Andrija Mohorovicic (1857--1936).