The Internal Layers & Structure of the Earth

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  • 0:00 A Hole to China?
  • 0:35 The Crust
  • 1:25 The Mantle
  • 2:00 The Core
  • 2:30 How Do We Know?
  • 3:30 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

While the Earth feels pretty solid, it's actually mostly liquid. Of course, the only reason we know all this is because of atomic weapons! As this lesson shows, studying the makeup of the Earth has been explosive at times.

A Hole to China

When you were a kid, did you ever try to dig a hole all the way to China? Or maybe you read 'Journey to the Center of the Earth' by Jules Verne, where three adventurers enter a volcano in an attempt to find out what exactly goes on in the deepest parts of our planet. However, your hole to China probably only went a few feet deep, and Verne's heroes end up going only from Iceland to Sicily. However, it was probably for the best that both of those missions failed. As we will see in this lesson, had either journey been more successful, the result would not have been a happy one.

The Crust

Every bit of human action in history that has happened on the ground has occurred on the crust. The crust is the outermost layer of the Earth. Comprised of large plates of land and between six and a hundred miles deep, humanity has never went further than the Earth's crust. These large plates are called tectonic plates, and their movements create everything from mountains and fertile valleys to earthquakes and volcanoes. The crust is made up of two parts, the continental crust and the oceanic crust. The continental crust, the part that is dry land, is much thicker than the oceanic crust, which is all the part underwater.

The crust also makes up part of the lithosphere, which literally means rock sphere. The lithosphere also includes the uppermost part of the mantle, the next layer down on our journey to the center of the Earth.

The Mantle

The mantle is by far the biggest part of the Earth - making up more than 85% of the Earth's mass! It is the layer upon which the tectonic plates float. However, the mantle is not exactly solid. Imagine a liquid with a consistency somewhere between a milkshake and saltwater taffy - not quite liquid, but not quite solid, either. This layer is extremely hot - and it's that heat that causes the tectonic plates to move. Imagine big chunks of chicken on top of a boiling soup, bouncing around, being moved from the heat below. That's what the heat of the center of the Earth does to the tectonic plates on top.

The Core

At the center of the Earth, below the mantle, is the core. The core has two different parts. The outer core is a molten layer of iron and nickel while the inner layer is made of solid iron. Why mostly iron? It is the densest of the common elements that make up the Earth, and over millions of years, much of the world's iron has been brought through the rest of the Earth because of gravity. The high pressure of the center of the Earth means that the inner core is solid, despite being the hottest part of the Earth. This iron creates the basis for a strong magnetic field, centered on the North and South Poles.

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