Here's a breakdown:
* Igneous rocks: These form from the cooling and solidification of molten rock (magma or lava). They are the foundation of the crust, formed from the initial volcanic activity that shaped the Earth. Examples include granite and basalt.
* Sedimentary rocks: These form from the accumulation and cementation of sediments, such as sand, silt, and the remains of organisms. They are found in layers on top of igneous rocks and often contain fossils. Examples include sandstone, limestone, and shale.
* Metamorphic rocks: These form when existing igneous or sedimentary rocks are subjected to intense heat and pressure, transforming their structure and composition. Examples include marble (from limestone) and slate (from shale).
It's important to note that the Earth's crust is not uniform in thickness. Oceanic crust is thinner and denser, primarily composed of basalt, while continental crust is thicker and less dense, with a higher proportion of granite.
