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Asthenosphere

The asthenosphere is the part of Earth’s mantle that is located below the lithosphere.

Illustration of the layers of Earth.
 
Scientists research earthquakes to study the parts of the Earth beneath the lithosphere.  Specifically, they look at the speed and direction. The waves of an earthquake can change these when the density of rocks changes within the Earth. Sometimes, the rocks in the asthenosphere can break apart. This is when a large earthquake occurs. 

What Is the Asthenosphere Made Of?

The asthenosphere is a layer of solid rock.  These rocks are tinier than the rocks in the lithosphere.  There are rocks in the upper mantle, and they can be part of both layers.  This is determined by the shape of the rocks.  Rocks typically in the lithosphere are solid and rigid.  This is different from rocks in the asthenosphere, which are flowing and can break apart. They exist in a molten form, called magma.

Thickness

The asthenosphere can extend from 60 miles to 450 miles below Earth’s surface. It’s also far more fluid than the lithosphere.

Why is the Asthenosphere so Hot?

It is believed that the asthenosphere is more fluid than the lithosphere. It is also believed that it is much hotter than the lithosphere.
Example of why the asthenosphere is hot.

Earth’s hot inner layers heat its outer layers.

 
There, it helps the rocks move without breaking or cracking. Because the rocks have so much pressure and heat on them, they can flow like they’re in liquid form.
 
This also causes the underside of tectonic plates to be smooth and allows them to move.  It almost seems like they’re “floating” on top of the rocks. Inside the asthenosphere, convection currents are created. These currents push magma through the tectonic plates. This magma then spreads above to create a new crust. 
 
This is not all the convection currents do. They also push and stress the lithosphere until it cracks. This is often what causes earthquakes to occur. It is believed that the old parts from the lithosphere are dragged down to the asthenosphere. These areas are known as subduction zones.
 
For more information, watch this video:  

Other Great Resources:

 
Kids Fun Science Article on the Subject: http://www.kids-fun-science.com/asthenosphere.html
 
Similar Kids Earth Science Article: http://www.kids-earth-science.com/asthenosphere.html
Written by: Lindley Lund.