FACTS : Inside the Earth

Probing the Earth

Scientists have worked out what the Earth's interior is like from vibrations from earthquakes and underground explosions.

Crust

The Earth has a thin shell of solid rock called the crust, which varies from 3-7 miles (6-11km) under the oceans to 18-12 miles (30-70km) under the continents.

Mantle

Beneath the crust is a layer almost 2,000 miles (3,200km) deep, called the mantle. It is so hot here that the rock flows very, very slowly.

Core

Below the mantle is a core of metal, mostly iron and nickel.

Outer core

The outer portion of the care is so ferociously hot that the metal is always molten.

Inner core

The Earth's inner core is even hotter-up to 12,600°F (7,000°c)- but the metal here is solid because pressures here are so great that metal simply cannot melt.

Earth has several different layers because the materials it is made of have separated out over billions of years. Dense metals such as iron sank to the center to form the core, while lighter rock- forming materials floated to the top to form the crust.