THE LAYERS OF THE EARTH

The Earth is divided into three chemical layers: the Core [Inner Core (D) and Outer Core (C)], the Mantle (B) and the Crust (A).

The Core is predominantly composed of iron and nickel. Even after 4.5 billion years of cooling, the Earth's core remains very hot. The Earth's core is divided into two layers, a solid inner core, and a liquid outer core. The Inner Core (D) (1216 km) is solid nickle-iron alloy. The Outer Core (C) (2270 km), is a molten nickle-iron alloy.

The Mantle (B) is approximately 2885 kilometers thick and is the middle layer of the Earth. The Mantle is made up of minerals rich in the elements iron, magnesium, silica, and oxygen. The Mantle makes up approximately ~85% of the Earth's volume. It is seperated from the crust by a sharp change to higher density and seismic velocity, and more mafic composition.

The Earth's outer layer, the Crust (A) is 4 to 60 kilometers thick. The Crust is rich in the elements oxygen and silica with lesser amounts of aluminum, iron, calcium, potassium, sodium, and magnesium. On the Earth, one finds two types of crust. Oceanic Crust is made of relatively dense mafic rock, called basalt. Continental Crust is made of lower density felsic rocks, such as andesite and granite.

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