Geology

Crust

The crust is Earth’s outermost layer. It is further divided into two categories—the thin oceanic crust that lies under the ocean basins and the thicker continental crust that forms the foundation for land on Earth.

Mantle

Earth’s mantle is the filling sandwiched between the crust and the core. It is 2,890 kilometers thick and can be divided into the upper mantle and the lower mantle. The upper mantle is closer to the crust. The temperatures in this region are cooler, resulting in rocks that are hard and brittle. The lower mantle is characterized by warmer temperatures and rock that is hot and soft.

Core

The core is the innermost region of the planet. It is divided into the outer core, which contains molten rock, and the inner core, which is under so much pressure that it prevents rock from becoming liquid. The core is Earth’s source of internal heat.

Plate Tectonics

Plate tectonics is the geological theory that the geosphere can be broken down into seven distinct large plates—the African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates—as well as several smaller plates.

According to the plate tectonics theory, these plates are all moving in different directions and at different speeds in such a way that they sometimes crash into or pull away from one another, causing such phenomena as earthquakes, volcanic eruptions, and rifts.

The regions where plates crash into one another are called convergent boundaries, while divergent boundaries occur when plates pull apart from one another. Places where plates slide past, or “side-swipe,” one another are called transform boundaries.