The interior of the Earth, similar to the other terrestrial planets, is chemically divided into 3 layers.
- The Crust. The Earth has an outer silicate solid crust.
- The Mantle. The Earth has a highly viscous mantle.
- The Core. The Earth has a liquid outer core that is much less viscous than the mantle, and a solid inner core.
The first is the uppermost division of the solid earth, representing less than 1% of its volume and varying in depth from 3 mi. to 37 mi. (5-60 km). Below the crust is the mantle, a thick, dense layer of rock approximately 1,429 mi. (2,300 km) thick. The core itself is even more dense, as illustrated by the fact that it constitutes about 16% of the planet's volume and 32% of its mass. Composed primarily of iron and another, lighter element (possibly sulfur), it is divided between a solid inner core with a radius of about 760 mi. (1,220 km) and a liquid outer core about 1,750 mi. (2,820 km) thick.
