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Earth's Interior

Exploring Inside Earth Geologists have used two main types of evidence to learn about Earth's interior: direct evidence from rock samples and indirect evidence from seismic waves.

Evidence From Rock Samples Geologists can learn about the Earth's interior by drilling for rocks or examining rocks that have been forced to the Earth's surface from as deep as 100 kilometers.

Seismic Waves There are different types of seismic waves. The speed and the paths they take tell us the structure of our Earth.

A Journey to the Center of the Earth There are three main layers of the Earth. The crust, the mantle, and the core. All three are different in their size, their composition, their temperature, and their pressures. In fact, they differ widely.

Temperature When you first dig through the surface of the Earth, the rocks are cool. This changes as you go deeper. 20 meters down they start to get warmer and then every 40 meters they get warmer by 1 degree Celsius. After 40 kilometers the warmth slows a little. The reason it is hot is because there are radioactive substances and there is heat left over from when Earth was formed.

Pressure There is pressure in the rock due to the weight above on the surface. The farther down you go the higher the pressure.

The Crust This area is the outer skin of the Earth. It is the solid rock that is dry land and that rock that is underwater. It is usually 5 to 40 kilometers thick. Oceanic crust is mostly basalt and Continental crust is mostly granite.

The Mantle There are 3 layers of the Mantle. The Mantle is very hot, solid rock. The three layers are: Lithosphere, Asthenoshere, and Lower Mantle. The Lithosphere is `100 kilometers thick and is closest to the crust. Then there is the Asthenoshere which is softer but still hard. The Lower Mantle is solid and goes all the way to the Core.

The Core The Core has two parts. A liquid outer core and a solid inner core. They are both made out of metal, nickel and iron. There is some evidence that there is some oxygen, sulfur, and silicon in the core.

Earth's Magnetic Field Scientists think that in the liquid outer core there are movements that create the magnetic forces of Earth.