Lobby > Exhibits > Why Geysers Erupt >Underlying Geology > Structure of the Earth

Yellowstone’s geologic story begins within the structure of the Earth. This structure gives rise to the geologic forces that shape the surface of our planet.

The Earth is composed of different layers. From the inside out, these are the core, the mantle, and the crust. Imagine you could take an elevator to the center of the Earth. The elevator would begin by falling between 3 and 30 miles (or 5 to 48 km) through a brittle layer of rock, which is called the crust. The thickness of the Earth’s crust varies, though usually the crust is thinner under the oceans.

After passing through the crust, the elevator slips down into the mantle. The mantle stretches for about 1,800 miles (2,897 km) and is the thickest layer of the Earth. The lower part of the mantle is made of semi-molten rock. From the lower mantle, the elevator enters the Earth’s outer core. This is the zone between the lower mantle and the inner core of the Earth. It’s extremely hot here—in fact, it is so hot that this layer is made of molten metals. Solid metal melts at about 2,000°F (1,093°C) and temperatures in the outer core are more than five times that hot! Finally the elevator passes into the solid inner core, stopping at the very center of the Earth. Altogether, it’s a journey of approximately 4,000 miles (6,437 km).

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