What is the Mantle?
The mantle is one of the three major layers of the Earth, which geologists often compare to a hard-boiled egg, with the mantle analogous to the white of the egg. The mantle is largest of the layers, making up about 83 percent of the Earth's volume.
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Origin
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The mantle, along with Earth's other layers, was created by heating that occurred in Earth's first 10 to 20 million years. Melted iron sank to the core of the new Earth, pulled by gravity, while lighter elements became the ocean and atmosphere. In between are the crust, which is also light, though heavier than atmosphere, and the mantle, which is heavier than the crust, but not as heavy as the core.
Materials
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The mantle is largely silicon and oxygen based with additional heavy elements like iron and magnesium. The upper portion of the mantle is strong and rocky. Underneath that, the mantle is still rock, but it is softened by heat and, thus, flows. The lowest part of the mantle is solid.
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Relation to the Earth's Other Layers
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The mantle lies between the core and the crust of the Earth; these regions are arranged in concentric layers. The mantle is the largest of the three sections. Along with the crust, the top part of the mantle makes up the rocky lithosphere, which is about 60 miles deep (about 96 km). The softened mantle section beneath is the asthenosphere, which reaches down about 220 miles (about 350 km). Beneath that is the lower mantle, which abuts the upper core.
Size
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There is no particular depth at which the mantle starts; that depends on the depth of the crust, which varies. Under the ocean, the crust is only a few miles deep, while in some places, the crust can reach about 60 miles (100 km) deep. The average is between 18 and 19 miles (30 km) deep. The mantle reaches down about 1,802 miles (2,900 km) to the core.
Effect on Earth's Surface
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It is from the upper mantle--the lithosphere and asthenosphere--that Earth's interior shapes Earth's exterior. The lithosphere floats over the flowing asthenosphere. The situation gives rise to earthquakes and mountain building. In some places, the mantle breaks through the crust in volcanic eruptions.
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