Rocks are cohesive, multicrystalline aggregates of one or more minerals. Intrusive igneous rocks, such as granite , crystallize from magma, molten material underneath the surface of the Earth. As compared to granite, basalt is much darker and is more dense. Sedimentary rocks , the most common type at the surface of the Earth, are rocks formed from the accumulation and lithification of sediments.
Sedimentary rocks contain the overwhelming majority of fossils.
Relative time relationships described by these names are based upon observed spatial relationships in the field. It decays to produce strontium-87, which is not produced through any other means on Earth. The Earth is internally divided into an outer, rigid crust, a mantle, and a core. The crust and the less rigid mantle are composed of silicate minerals, the core largely of metallic iron. Although slow on human time scales, over the vast span of geologic time, plate motion has caused the positions and orientations of the continents to change dramatically.