The interior of the Earth, similar to 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. Many of the rocks now making up the Earth's crust formed less than 100 million (1 ) years ago; however the oldest known mineral grains are 4.4 billion (4.4 ) years old, indicating that the Earth has had a solid crust for at least that long.

Much of what is known about the interior of the Earth has been inferred. The force exerted by Earth's gravity is one measurement of its mass. After measuring the volume of the planet, its density can be calculated. Astronomers also have performed similar planetary measurements. Calculation of the mass and volume of the surface rocks and bodies of water allow estimation of the mass, volume and density of surface rocks. The mass which is not in the atmosphere, oceans, and surface rocks must be in deeper layers.