What is the athenosphere and where it located?

The asthenosphere is a layer of the Earth's mantle that is located beneath the lithosphere and above the mesosphere. It is a zone of relatively weak and partially molten rock that exhibits plastic-like behavior and allows the lithosphere to move above it.

Location:

The asthenosphere lies between approximately 100 to 400 kilometers (60 to 250 miles) below the Earth's surface. It is present beneath the entire lithosphere, including both the continental and oceanic plates.

Characteristics:

1. Temperature: The asthenosphere is characterized by higher temperatures compared to the overlying lithosphere and the underlying mesosphere. The increasing temperature with depth causes the rocks in the asthenosphere to become weaker and less rigid.

2. Partial Melting: The asthenosphere contains a significant amount of partially molten rock, also known as magma, which makes it behave like a viscous fluid over long timescales. This partial melting is due to the combination of high temperature and the presence of volatile substances such as water and carbon dioxide.

3. Mantle Convection: The asthenosphere is where the Earth's mantle convection currents occur. These convection currents are driven by the heat transfer from the Earth's interior to the surface, causing the solid rock to rise and sink in a convective motion. The asthenosphere's weak and partially molten state facilitates this convective movement of mantle material.

4. Lithosphere-Asthenosphere Boundary: The boundary between the lithosphere and the asthenosphere is often defined by the change in seismic wave velocities. The seismic waves travel faster in the rigid lithosphere and become slower in the weaker asthenosphere. This change in velocity is attributed to the change in rock properties and the presence of partial melts.

The asthenosphere plays a crucial role in several geological processes, such as plate tectonics, mountain building, and volcanic activity. It is the weak layer that enables the rigid lithosphere to move and deform, leading to plate motions, earthquakes, and the formation of mountain belts.