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The Layers of the Earth: Facts, Composition & Temperature

The Layers of the Earth: Facts, Composition & Temperature
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  • 0:21 Chemical Layers
  • 0:53 Earth's Crust
  • 2:02 Mantle
  • 2:45 Core
  • 3:28 Temperatures
  • 4:16 Other Layers
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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.

This lesson will discuss the layers that make up the inside of the Earth chemically, including their composition, temperatures, and the states. A short quiz will follow.

The Earth as a Layer Cake

Imagine the Earth as a gigantic layer cake, with colorful angel cake layers, cream fillings, and fondant icing on the top. Feeling hungry yet? Unfortunately, the earth isn't actually filled with gooey sweets, but it does have various layers laid out just like a cake.

Chemical Layers

In 1692, Edmund Halley proposed a hollow model for the Earth. Based on Newton's laws, it seemed like the Earth couldn't possibly be solid. Instead, he thought it must contain a series of hollow shells. It turned out Newton's laws were right but at the time, ideas about the density of the Earth and Moon were very wrong.

Today, there are a number of different ways of defining the layers of the Earth, but the most common one is based on chemical composition or the elements and molecules present in each part of the Earth's interior.

The Earth's Crust

At the very surface of the Earth is the crust, the topmost layer, made mostly out of solid silicate rocks like basalt and granite. The crust is like the icing on a cake, though not nearly so tasty. We humans live on top of the crust; you can think of us as the strawberries or gummy bears on the top of the cake. But to keep the analogy more to scale, we would be a lot closer to a sprinkle of confectioner's sugar. We're actually super tiny, compared to the size of the crust.

The crust is a ridiculously thin layer when the Earth's interior is drawn to scale. So small that it wouldn't show up on most diagrams. But despite being tiny compared to the rest of the layers, the crust can be a whopping 70 kilometers thick!

Continental crust, the crust under which the continents are built, is 10-70 km thick, while oceanic crust, or the crust under the oceans, is only 5-7 km thick. The deepest mine shaft ever built, Western Deep in South Africa, currently reaches 3.9 km, which barely scratches the surface of the continental crust.

The Mantle

Underneath the crust is the mantle, the largest layer, composed of rocky oxides and silicates under high pressure. We once thought the mantle contained liquid magma, but we now know that is not the case; magma is formed only in certain locations, due to the high pressures and temperatures. The mantle is huge, going down to a depth of 2,500 km and is like the main part of the cake.

The mantle is sometimes split into the upper mantle and lower mantle because the upper part of the mantle moves and flows in convection currents much more easily than the lower part. Even solid rock can move and flow at these high pressures and temperatures, though it moves very slowly.

The Core

Below the mantle is the core, which is the very center of the Earth, made mostly of metals like iron. The outer core is a liquid that flows in circles. This is like the delicious cream filling of the cake! In fact, the liquid flow of the outer core is responsible for creating the Earth's magnetic field. The inner core, on the other hand, is the solid part that is believed to contain at least 90% iron, which is like a central layer of dense pound cake.

The outer core goes from a depth of 2,550 km down to 4,750 km, and the inner core continues to the center of the Earth at a total depth of 6,470 km.

Temperatures

Let's imagine we could build a craft and dig all the way to the center of the Earth. How hot would it get along the way? As we went deeper under the Earth, the temperatures would get hotter and hotter. The oven where we baked the cake doesn't even register when compared to the temperatures under the Earth.

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