What is the difference between asthenosphere and lithosphere?
The asthenosphere and lithosphere are two distinct layers of
the Earth's uppermost structure, both located in the outermost shell known as
the geosphere. They have different properties and play crucial roles in the
dynamics of the Earth's lithosphere and tectonic plate movements. Here are the
key differences between the asthenosphere and lithosphere:
1. Definition and Composition:
- Asthenosphere:
The asthenosphere is a partially molten, ductile region located in the
upper mantle of the Earth, situated just below the rigid lithosphere. It
extends from about 80-200 kilometers (50-124 miles) below the Earth's
surface. The asthenosphere is composed of solid rock that behaves in a
semi-fluid manner due to the high temperatures and pressure, allowing it
to slowly flow over geological timescales.
- Lithosphere:
The lithosphere, on the other hand, is the rigid, outermost layer of the
Earth's geosphere. It consists of the Earth's crust and the uppermost
portion of the mantle and is divided into several large and small tectonic
plates. The lithosphere varies in thickness but is typically around 100
kilometers (62 miles) deep.
2. Physical State:
- Asthenosphere:
The asthenosphere is partially molten and behaves in a plastic or
semi-fluid manner. It is soft and capable of slowly flowing, which is an
essential factor in plate tectonics and the movement of tectonic plates.
- Lithosphere:
The lithosphere is rigid and behaves like a solid. It is comparatively
stiff and brittle, making it capable of supporting loads and resisting
deformation.
3. Tectonic Plate Movement:
- Asthenosphere:
The flow and movement of the semi-fluid asthenosphere are crucial for the
motion of tectonic plates. Tectonic plates "float" on the
flowing asthenosphere and move due to the forces generated by convection
currents in the partially molten layer below.
- Lithosphere:
Tectonic plates are a part of the lithosphere. These plates are distinct
sections of the Earth's rigid outer shell that move due to the underlying
flow in the asthenosphere. Their movement and interactions at plate
boundaries lead to various geological phenomena like earthquakes,
volcanoes, and mountain formation.
4. Depth:
- Asthenosphere:
The asthenosphere extends from a depth of about 80-200 kilometers (50-124
miles) below the Earth's surface.
- Lithosphere:
The lithosphere starts from the Earth's surface and extends to a depth of
about 100 kilometers (62 miles).
In summary, the asthenosphere is a partially molten, ductile
layer in the upper mantle that flows slowly and plays a significant role in the
movement of tectonic plates. In contrast, the lithosphere is the rigid outer
layer of the Earth consisting of the Earth's crust and uppermost mantle, and it
includes the tectonic plates themselves