Science Olympiad Dynamic Planet Practice Test

Which layer is often described as a soft, flowing layer of the mantle?

1. Asthenosphere

2. Lithosphere

3. Outer core

4. Crust

The correct answer is: Asthenosphere

The asthenosphere is the layer of the mantle that is often described as a soft, flowing layer. This region is located beneath the lithosphere and extends down to about 700 kilometers in depth. The asthenosphere is characterized by its ability to flow and deform over geological time scales due to the high temperatures and pressures present at that depth. This flowing behavior allows tectonic plates, which are part of the lithosphere, to move over the asthenosphere, enabling plate tectonics and the occurrence of earthquakes and volcanic activity. The lithosphere, on the other hand, is the rigid outer layer of the Earth, comprising the crust and the uppermost part of the mantle. While it is strong and brittle, it does not exhibit the same flowing properties as the asthenosphere. The outer core is primarily a liquid layer composed mainly of iron and nickel, and it plays a crucial role in generating the Earth's magnetic field, but it is not part of the mantle. The crust is the outermost solid layer of the Earth and is distinct from the mantle. Thus, the asthenosphere is accurately described as a soft, flowing layer of the mantle due to its capacity to deform and facilitate tectonic movement.