Astenosfäärillä

Astenosfäärillä is the upper layer of the Earth's mantle, lying just below the lithosphere. It is a region of the mantle that is partially molten or ductile, meaning it can flow very slowly over geological timescales. This plasticity is crucial for plate tectonics, as the rigid lithospheric plates are thought to float and move upon the asthenosphere.

The asthenosphere extends from a depth of about 100 to 200 kilometers (60 to 125 miles) below the Earth's surface, though its exact thickness can vary. Its temperature is high enough for some rock to melt, creating a viscous, semi-fluid zone. This partial melting is facilitated by the extreme pressure and heat found at these depths.

The slow convection currents within the asthenosphere are believed to be the driving force behind the movement of tectonic plates. Hotter, less dense material rises from deeper within the mantle, while cooler, denser material sinks, creating a circulatory motion. This movement exerts stress on the overlying lithosphere, causing it to break into plates and interact at their boundaries. Volcanic activity and earthquakes are often associated with these plate interactions, which are ultimately powered by the dynamics of the asthenosphere.