The layer of the Earth made up of solid rock is called the crust. The crust is the outermost layer, varying in thickness, being thinner under oceans (oceanic crust) and thicker under continents (continental crust). It is composed of various rock types, including igneous, sedimentary, and metamorphic rocks. The crust is essential for supporting ecosystems and human activities and plays a significant role in plate tectonics and geological processes. Interaction with the underlying mantle leads to various geological phenomena such as earthquakes and volcanic activity.