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Earth is composed of three layers: the outermost crust, the middle region called the mantle and the innermost region known as the core.
The crust is the layer on which we live and it houses all the oceans and continents. It has a variable thickness (between 5-70 kilometers). The crust is thin under oceans and thicker under continents. It is composed mostly of silicate rocks (e.g., basalt and granite). The middle layer, the mantle, is about 2,900 kilometers thick and is composed of highly dense silicate rocks. This region is the thickest among the three layers and is rich in iron and magnesium. Contrary to common belief, this layer is not made of magma and is liquid only in places. For the most part, the mantle is a plastic solid. Earth's core is divided into inner (about 1200 km thick) and outer (about 2200 km) core. The inner core is mostly iron and is solid, while the outer core is a rotating iron-nickel alloy liquid. It is the rotation of this outer core that gives Earth its magnetic field.
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