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
History of geology the investigation of the Earth's history, the study of geology could become a distinct field of science. To begin with, the terminology and definition of what constituted geological study had to be worked out. The term "geology" was first used technically in publications by two Genevan naturalists, Jean-André Deluc and Horace-Bénédict de Saussure, though "geology" was not well received as a term until it was taken up in the very influential compendium, the "Encyclopédie", published beginning in 1751 by Denis Diderot. Once the term was established to denote the study of the Earth and its history, geology slowly became more