If scientists have never studied any materials from a depth below 7 miles (11km), then how is it that we know what is in the center of the Earth? How can we know what the core of the Earth is made of, if we have never seen it?
The answer is actually quite simple. While it is true that we cannot study the Earth’s core using visible light, we can study it using other senses. The most important thing we use to sense the Earth’s core are seismic waves. Seismic waves are waves of energy caused either by earthquakes or by massive man-made explosions.
Scientists are able to measure these waves as they pass through the Earth. As these waves encounter different materials, they change in important ways, becoming longer, shorter, faster, or slower. Geologists study these changes in the waves, and are able to draw conclusions about what the core of the Earth must look like.
Geologists also can learn a lot about the core of our planet by looking at Earth’s magnetic field. The Magnetic field is created by massive circulations of hot liquid mantle beneath the Earth’s surface.
These clues lead geologists to believe that the Earth is made of four distinct layers. These layers are the crust, the mantle, the outer core, and the inner core.