The lithosphere is the rigid, outermost rocky shell of a terrestrial planet, such as Earth. On Earth, it includes both the crust and the uppermost part of the mantle, called the lithospheric mantle, which behaves elastically over long time scales

. Key characteristics of the lithosphere:

• It is solid and brittle, extending from the Earth's surface down to about 80 to 120 kilometers (roughly 50 to 75 miles), though thickness varies depending on location (thinner under oceans, thicker under continents)

• It is divided horizontally into tectonic plates that move and interact, causing geological phenomena like earthquakes, volcanic eruptions, and mountain formation

• The lithosphere "floats" on the softer, more ductile asthenosphere beneath it, which allows the plates to move

• The oceanic lithosphere is denser and thinner, mainly composed of basalt, while the continental lithosphere is thicker, less dense, and composed mostly of granite

The term "lithosphere" comes from the Greek words lithos (rocky) and sphaera (sphere), reflecting its nature as the Earth's rocky outer shell

. In summary, the lithosphere is Earth's strong, rigid outer layer made up of the crust and upper mantle, broken into tectonic plates that shape the planet's surface through their movements