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Earth’s Outer Core

The outer core is a layer of the Earth that makes up the top part of the Earth’s core. It’s found close to the center of the Earth, very far away from the surface. Because it is so hot, this layer is made of melted metal (in the form of magma). It’s unique because it is liquid, unlike the other layers of the Earth.    An illustration of a cutaway of the earths layers.

Where is the Earth’s Outer Core?

The outer core is located between the Earth’s mantle and the Earth’s inner core. It starts at the bottom of the mantle, about 2,700 km below the surface of the Earth. It ends at the beginning of the inner core, which is 5,150 km from the crust.

An illustration of the structure of Earth, as it would look if you took out a wedge.

Can you find the outer core? Look between the inner core and the lower mantle.

Each year, part of this layer freezes and becomes part of the solid inner core. So over time, the inner core gets a little bit bigger while the liquid part of the core gets smaller. 
 

Characteristics of the Earth’s Outer Core

Temperature: The temperature is not the same throughout the entire layer. At the top, it is about 3,000 degrees Celsius. At the bottom, it can get to 7,500 degrees Celsius. That’s really hot! However, the outer core is slowly cooling off as it transfers some of its heat to the mantle. This may contribute to the formation of mantle plumes.
 
Thickness: This layer of the Earth is about 2,400 km thick. It is less thick than the mantle but thicker than the inner core. Like the other layers of the Earth, the outer core is thicker in some places and thinner in others.  
 
Composition: The outer core is mostly made out of iron. It also contains some nickel and possibly oxygen and sulfur. 
 
State: Unlike the inner core and the mantle, this layer is in a liquid state. This is because it is so hot, so all the rock melts.   
 

Magnetism: Since this layer is liquid, it moves around the inner core. This creates the Earth’s magnetism! 

An illustration of what it would look like to be surrounded by lava.

The outer core is super hot and in a liquid state. You do not want to go swimming in this!

The Discovery

You might be wondering how scientists discovered the Earth’s core. Watch this video to learn how scientists discovered the Earth’s outer core. Hint: It has to do with seismic waves.
 

Other Great Resources

Brief Overview of the Earth’s Layers: http://gamediv1.weebly.com/outer-core.html

Science Magazine on the Core: http://www.sciencemag.org/news/2010/08/earths-moving-melting-core

The Core and the Structure of the Earth: https://www.dkfindout.com/us/earth/structure-earth/outer-core/

Written By: Leah Tolby