Earth's Internal Layers: Crust, Mantle & Core

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  • 0:06 Earth's Core
  • 1:32 The Mantle
  • 2:44 The Lithosphere
  • 3:32 The Crust
  • 4:48 The Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Earth is made up of several different layers, each with unique properties. In this video lesson, you will identify each layer of Earth and how it relates to Earth as a whole.

Earth's Core

You may have heard that ogres are like onions because they have many layers. Well, Earth is the same way! Earth is made up of several different layers, each of which has unique properties.

Let's start from the inside and work our way out. Earth has a core, but this is really two distinct parts: the inner core and the outer core. Both parts of the core are made up of mostly iron and some nickel. The difference is that in the inner core, those minerals are solid and in the outer core, they're liquid.

The inner core of the earth is incredibly hot - so hot that if you tried to dig a hole to China, you'd burn up on your way through the earth! What's amazing about the inner core is that even though it's about as hot as the surface of the sun, there's so much pressure from the weight of the world pushing down on it that it can't melt. This is the same reason that water in a pressure cooker doesn't boil, no matter how hot it gets!

The outer core is also made up of iron and nickel, but it's quite different because it is a liquid. This is because there is much less pressure on this layer than the one below it (the outer core adds a lot of pressure to the inner core!). Though the flow of this liquid layer is very slow-moving (about a few kilometers a year), it is what produces Earth's magnetic field. Our North and South Poles exist because of this liquid outer core, even though it's almost 2,000 miles below us.

The Mantle

Sitting on top of the outer core, we find the mantle. This layer is by far the thickest layer of Earth, about 1,800 miles thick! It also makes up about 85% of Earth's volume. Like the core, the mantle contains mostly iron, but in the form of silicate rocks. You might be surprised to learn that this rock actually moves like a fluid, similar to how silly putty moves. If you poke silly putty hard, it acts like a solid, but if you slowly pull it apart, it acts like a liquid. We call this ability of rock to move without breaking plasticity.

The mantle can also be divided into two portions, the upper mantle and the lower mantle. The lower mantle is completely solid because, like the solid inner core of Earth, the pressure is just too great for it to melt and flow. The upper mantle is also known as the asthenosphere, which flows as convection currents. Convection occurs in all fluids and is the rising of warm particles and sinking of cool particles. So, as the material in the upper mantle warms, it rises straight up, and as it rises, it cools and then sinks back down.

The Lithosphere

This convection flow of the asthenosphere has a large impact on Earth's lithosphere, the outermost layer of the planet. The lithosphere is only about 60 miles thick and contains both the crust and a small portion of the upper mantle. The lithosphere is very rigid; it does not flow like the asthenosphere but instead floats on top of it like ice on a pond.

This layer of Earth is broken up into several different pieces, like a jigsaw puzzle called tectonic plates. The convection currents below in the mantle move these plates around on the surface of Earth. Though the 'flow' of the asthenosphere is on par with a snail's pace, these enormous plates running into each other is what causes earthquakes, volcanoes and mountain range formation.

The Crust

The crust itself, which is contained in the lithosphere, can also be divided into two parts (have you noticed a pattern yet?). We live on the continental crust, and the ocean floor is made up of the oceanic crust. The continental crust is thicker than the oceanic crust, but it's made up of rock that is less dense than the oceanic crust, so it sits on top of it, above sea level.

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