Nobody has journeyed to the center of the Earth to see what it is like. However, scientists using seismic waves have developed models showing what the Earth is made of and the thickness of the different layers.

Click on the labels to learn more about Earth's layers.

Crust
The crust is the Earth’s thin outer rind. It accounts for only 0.4 percent of the Earth's mass. The boundary between the crust and the mantle is called the Mohorovicic Discontinuity or MOHO for short.
There are two types of crust:
1.) The continental crust is 30-70 kilometers thick. It is made of all three types of rocks; igneous, sedimentary, and metamorphic. Most of these rocks are made of 60 to 70 percent silica (or quartz).

2.) The oceanic crust is only six kilometers thick. It is composed of layers of igneous rocks that contain 50 to 60 percent silica. These rocks have more iron and magnesium than those in the continental crust. Magma that erupts onto the ocean floor cools quickly, forming pillow lava. Over thousands of years, the remains of shells and microscopic plants and animals rain down, blanketing the deep ocean floor under a layer of sediment.

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Upper Mantle
The upper mantle is 400 kilometers thick. It is weaker than the rest of the mantle and bends and flows under pressure. Like the lower mantle, the upper mantle is made up of minerals rich in iron, silica, magnesium, and oxygen.

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Lower Mantle
The solid lower mantle is 2,500 kilometers thick. It is composed of minerals rich in iron, silica, magnesium, and oxygen. Together, the upper and lower mantle make up two-thirds of the Earth's mass.

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Outer Core
The liquid outer core is about 2,300 kilometers thick. It contains molten iron and nickel.

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Inner Core
The solid inner core extends about 1,200 kilometers from the center of the Earth. It is mostly made of solid iron and nickel.

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