THE ASTHENOSPHERE: "WEAK ROCK"
The Earth is composed of 5 layers:
1) The Inner Core
2) The Outer Core
3) The Mantle: Lower Mantle & Upper Mantle/Asthenosphere
4) The Lithosphere: Continental Crusts & Oceanic Crusts
5) The Atmosphere
Characteristics of the Asthenosphere
- located in the upper mantle
- there is so much heat and pressure in the upper mantle that the asthenosphere can flow like liquid even though it is a solid rock
- low density
- seismic waves pass through the asthenosphere slower than the waves that pass through the lithosphere
- the asthenosphere is much closer to earth's surface when it is under oceanic crusts
- at mid-ocean ridges, the asthenosphere will sometimes rise through surface
Mantle Convection Cells
Because of the heat that is emitted from the cores, the rock in the mantle heats and rises until it reaches the top of the upper mantle. Once it reaches the top of the upper mantle, the rock will push in all directions and eventually travel back down and cool. The cycle then repeats itself. This is called a convection cell
Since the asthenosphere is less dense than the lithosphere, the continental and oceanic crusts float on the asthenospheric rock. So because the asthenospheric rock is a part of the convection cell cycle, the crusts are impacted by the movement of the asthenosphere. When the asthenosphere moves, so do the crusts that rest on top of it. This is what creates continental drift.
Ridges and Trenches
Convection cells also create ridges and trenches within the crusts. When the asthenospheric rock is rising to the top of the upper mantle because of heat, it will eventually reach the lithosphere and can pass through it. This will add more rock to the crusts, which then creates an ridge.
In a reverse fashion, the asthenospheric rock will eventually cool and begin to travel back down towards the core. When the asthenosphere does this, it will pull the crust that is floating above it along with it, so the crust will be dragged into the upper mantle. This will create a trench.
The Asthenosphere's Impact
The movement of the asthenosphere is the foundation of the study of Plate Tectonics, which focuses on continental drift, earthquakes, etc.