Crust (geology) magma ocean and floated to the top; however, it is unlikely that Earth followed a similar pattern, as the Moon was a water-less system and Earth had water. The Martian meteorite ALH84001 might represent primary crust of Mars; however, again, this is debated. Like Earth, Venus lacks primary crust, as the entire planet has been repeatedly resurfaced and modified. Secondary crust is formed by partial melting of silicate materials in the mantle, and so is usually basaltic in composition. This is the most common type of crust in the Solar System. Most of the surfaces of Mercury, Venus, Earth, and
Earth Revealed: Introductory Geology Earth Revealed: Introductory Geology Earth Revealed: Introductory Geology, originally titled Earth Revealed, is a 26-part video instructional series covering the processes and properties of the physical Earth, with particular attention given to the scientific theories underlying geological principles. The telecourse was produced by Intelecom and the Southern California Consortium, was funded by the Annenberg/CPB Project, and first aired on PBS in 1992 with the title "Earth Revealed". All 26 episodes are hosted by Dr. James L. Sadd, professor of environmental science at Occidental College in Los Angeles, California. Some footage used in "Earth Revealed" previously had been seen in the