The interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The liquid outer core gives rise to a weak magnetic field due to the convection of its electrically conductive material.
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The interior of the Earth reaches temperatures of 5650 ± 600 kelvins [3] [4]. The planet's internal heat was originally generated during its accretion (see gravitational binding energy), and since then additional heat has continued to be generated by the decay of radioactive elements such as uranium, thorium, and potassium. The heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the Sun.
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Seismic measurements show that the core is divided into two parts, a solid inner core with a radius of ~1220 km and a liquid outer core extending beyond it to a radius of ~3480 km. The solid inner core is generally believed to be composed primarily of iron and some nickel. Some have argued that the inner core may be in the form of a single iron crystal. The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements. It is generally believed that convection in the outer core, combined with stirring caused by the Earth's rotation (see: Coriolis effect), gives rise to the Earth's magnetic field through a process described by the dynamo theory. The solid inner core is too hot to hold a permanent magnetic field (see Curie temperature) but probably acts to stabilise the magnetic field generated by the liquid outer core.
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Finally, vulcanism continuously emits water vapor from the interior. Earth's plate tectonics recycle carbon and water as limestone rocks are subducted into the mantle and volcanically released as gaseous carbon dioxide and steam. It is estimated that the minerals in the mantle may contain as much as 10 times the water as in all of the current oceans, though most of this trapped water will never be released.