The Earth's lithosphere is the outermost layer of the planet, consisting of the crust and the upper part of the mantle. It is rigid and relatively cool compared to the layers beneath it. The lithosphere is divided into tectonic plates, which float on the semi-fluid asthenosphere below. These plates are responsible for many geological processes, including earthquakes and volcanic activity. The lithosphere varies in thickness, being thicker under continents and thinner under oceans. It plays a crucial role in supporting life by providing essential minerals and nutrients. Additionally, the lithosphere interacts with the atmosphere, hydrosphere, and biosphere, making it vital for Earth's ecosystems.