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
The Layer Monument Layer Quaternity correspond to the alchemical "deities" of Apollo, Luna, Mercurius and Vulcan as named in "Atalanta Fugiens" (1617) by the German alchemist-physician Michael Maier (Emblem XVII). Collectively the Layer Quaternity are a unique alchemical mandala. Through polarized symbolism they delineate essential coordinates associated with Mandala art, namely Space (Heaven and Earth) and Time (Young and Old). Utilizing variety and multiplicity, key attributes of Northern Mannerist art, they also represent fundamental aspects of the human condition, namely, gender, youth and age, pleasure and suffering. A fifth, uniting symbol, a skull, is located at the very centre of the monument. The