More directly, residual organic materials related to life and its origin can be sought. For Mars, the most promising planet besides Earth for the development of life, this level of understanding is being urgently and actively sought. Early in its history, the Earth underwent extensive, internal chemical separations to produce a large metallic core, a thick silicate mantle, and a thin crust. Heat produced within the planet drives the continents to move about, as parts of lithospheric plates. The floors of the oceans are divided by volcanic centers known as ridges, where fresh lava pours out to produce new ocean floor.
Water causes erosion of the continents and produces sedimentary rocks.
Water also affected the chemical separations that produced the continental rocks. Earth chemistry is exceedingly complex, and has thus produced a wide variety of igneous, sedimentary, and metamorphic rocks. The Moon also underwent extensive and complex chemical separations very early in its history, and those separations produced a mantle and a crust, but little or no metallic core. There are no lunar lithospheric plates and probably never were any. The youngest lunar lavas sampled are more than 3 billion years old.