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The lithosphere is the Earth’s rigid outer shell, comprising the crust and the uppermost ~30–50 km of the mantle. It is the only layer that participates in plate tectonics.
Geologists divide the planet into three mechanical layers: the lithosphere, the more ductile asthenosphere beneath it, and the hot, viscous mesosphere that overlies the core. The lithosphere “floats” on the asthenosphere, allowing it to slide as tectonic plates.
Heat transfer from the interior drives mantle convection, which in turn moves the plates. This dynamic process shapes mountains, creates mid‑ocean ridges, and powers volcanic activity.
Because the lithosphere extends from the surface to the top of the upper mantle, it covers 100 % of the planet. Its thickness, however, varies with location. For broad calculations we often use an average of 100 km. With Earth’s equatorial radius at 6,378 km (NASA), the lithosphere represents roughly 1.5 % of the total radius—a thin, but life‑supporting shell.
Below this layer, temperatures rise to about 1,832 °F, and the boundary between the lithosphere and asthenosphere plays a key role in generating seismic and volcanic events.
The crust is thinner under the oceans (5–10 km) and thicker on continents, reaching up to 60 km beneath mountain ranges. The mantle portion of the lithosphere ranges from ~50 km to 100 km, yielding an average lithosphere depth of 70–100 km.
These spatial differences, combined with the temperature contrast between the lithosphere and the underlying asthenosphere, explain why earthquakes, continental drift, and volcanoes are most common along plate boundaries.
