Outer Core of the Earth: Definition, Composition & Facts

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  • 0:04 Earth's Layers
  • 0:55 Composition of the Core
  • 1:40 Making the Earth Magnetic
  • 3:12 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn about the outer core of the earth, including its temperature, composition and state, as well as how the motion of the outer core creates the earth's magnetic field. Then, test your knowledge with a short quiz.

Earth's Layers

We all have that person in our family who is pretty complex and multi-layered, the one who you never know what they'll do next! Well, it turns out that the earth is pretty similar—it has many layers. One of those layers is called the outer core.

Once upon a time, we thought the earth was hollow—even Newton's laws seemed to suggest it must be. But once we came up with a more accurate figure for the density of the earth, we realized that it wasn't hollow at all. Rather, the earth was like a sandwich of very different layers, all the way down.

There are a number of ways of defining the layers of the earth, but chemical composition—based on the elements present in different parts of the earth—is the most common way. If you use this method of layering, you come up with four main layers for the earth: the crust, the mantle, the inner core, and the outer core.

Composition of the Core

The core of the earth is the center. The inner core is solid and is 90% iron, but the outer core is a liquid...and it's a good thing it is! More on that later. The outer core is made of a mixture of iron and nickel, with smaller amounts of silicon and oxygen.

The outer core officially begins at a depth of 2550 km below the earth's surface, down to a final depth of 4750 km at the boundary between the inner and outer core. As you move through this depth, the temperature increases from 4500 degrees Celsius to a final temperature of 5500 C. At these temperatures, many metals, such as copper, would boil, if there weren't so much pressure holding them together.

Making the Earth Magnetic

As mentioned previously, it's a good thing the outer core is liquid. This is because it's responsible for the earth's magnetic field. Every day the earth is bombarded by charged particles and radiation from the sun, in quantities that would be extremely dangerous to humans and could give us all cancer.

But thanks to the earth's magnetic field, most of these particles are pushed out of the way and funneled to the North and South Magnetic Poles. There, they enter the earth safely, creating a beautiful light display called the Aurora Borealis, or northern lights, in the Northern Hemisphere and the Aurora Australis, or southern lights, in the Southern Hemisphere.

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