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Earth
E
Earth
The third planet from the Sun. It orbits between 147,099,590km from the Sun in January and 152,096,150km in July. From space it appears as a small blue planet.
It has a diameter of 12,756km and orbits the Sun every 365.25 days.
The Earth has an atmosphere made of 78% nitrogen, 21% oxygen, and 0.9% argon. There are smaller amounts of carbon dioxide, water vapor, hydrogen, and other gases. Because the water vapor changes to water droplets when
it makes cloud, the surface of the Earth is often obscured from space.
The Earth is like a ball within a shell within a shell. The innermost
part of the Earth is called the core, the shell around it is called the mantle, and it is surrounded by the thin shell that we call the crust.
The core and the mantle together make up almost all of the Earth. They are the source of the Earth’s magnetism, volcanoes and all of the material that a volcano sends out, and of earthquakes. The crust—the rocks on which we live—is a thin, brittle “skin” on an Earth scale.
The core
Imagine being squashed under 6,000km of rock. This is exactly what it is like at the center of the core. The rock around the core acts like a blanket, keeping the heat in—you can start to see why the core is both very hot and why its materials are very compressed.
The center of the core is a vast liquid ball of white-hot nickel and iron. This inner part of the Earth is a kind of furnace, with the heat trying to get out.
The outer part of the core is not quite as hot, and it is nearly solid. The heat from the furnace in the center of the core heats these rocks and makes them move slowly,
just as water moves in a pot that is heated on a stove. This kind of movement is called convection.
As the iron-rich rocks slowly move around, they create the Earth’s magnetism. So when we use a compass, we are making use of magnetism formed over 3,000km below our feet!
The mantle
The rock surrounding the core is made mainly of the metals magnesium and iron.
The mantle is about the same distance across as the core—some 3,000km. Most of it is solid, but
 Earth—The Earth has a thin, cold, and brittle shell called the crust that contains a hot mantle. Below the mantle is the core.
The crust is made largely of hard rock.
The region below the crust is called the mantle. Hot liquid rock sometimes bursts through the crust to make volcanoes.
The Earth has a hot liquid core made largely of iron. This is where the Earth’s magnetism is made.
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