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The solid surface we stand on is just one of the layers of the Earth. In fact, it’s the only one we can survive on. If you could dig down through the Earth’s layers, you would find temperatures and pressure rising to the point that rock melts and beyond.
Let’s take a look at the Earth layers, starting with the inside.
The very center of the Earth is known as the core. This is actually comprised of a solid inner core with a radius of 1,220 km, and then a liquid outer core that extends out to 3,400 km. Scientists think that during the Earth’s formation, the heaviest elements – like iron – sunk down to the center of the Earth and helped to form this core. We know that the Earth’s core rotates, generating a magnetic field that protects us from the Sun’s solar wind. Nobody really knows how hot it is down there, but scientists think it’s probably 3,000-5,000 Kelvin.
Outside the core is the mantle,; the thickest part of the Earth’s interior layers. This is a vast underground ocean… of liquid rock! The lave we see pouring out of volcanos comes from the mantle. The heat released from the Earth’s core drives convection in the mantle, and the crust’s tectonic plates serve to stir up the mantle as well. Hotter material rises, and relatively cooler blobs of rock sink down through the mantle.
The outermost layer of the Earth is the crust – the cooled and hardened part of the Earth. That’s what you’re standing on right now! The depth of the crust varies from 5 km underneath the oceans and 30 km thick underneath the continents. You might be surprised to know that the Earth’s crust only accounts for about 1% of the entire volume of the Earth.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.