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TITLE: The Inner Earth


[Photo: Layers of the Earth]
The inner Earth is layered. Beneath its familiar surface and thin crust lie a rocky mantle and iron core.

The inner Earth is hot. Its core is hotter than the surface of the Sun. The escape of this inner heat to cold outer space causes the tectonic plates to move.

The inner Earth flows and churns. In the mantle, flowing rocks help move the plates above them. In the outer core, a churning dynamo of liquid iron generates Earth's magnetic field.

During Earth’s first 100 million years, ever-larger particles in the infant Solar System collided and stuck together — generating tremendous heat.

Earth accreted, then melted completely, and layers began to form.

  • Dense molten iron sank and created the core.
  • Lighter silicate liquid rose and cooled, forming the mantle.
  • Later, partial melting of the mantle produced the crust — a process that continues today.

 





The Crust – Earth’s
Thin Skin

Relative to its size, Earth's crust is about as thin as an apple's skin. This outermost layer is composed primarily of two types of rock.

Granite
The continental crust is mostly granite.

Basalt
The oceanic crust is mostly basalt.

  [Photo: Granite and Basalt]

The Mantle – Deep and Dense

About 84 percent of Earth's volume is mantle rock.

  • The uppermost 100km of the mantle is rigid. Along with the crust, it makes up
    the lithosphere (the plates).
  • The next layer, the asthenosphere, is solid, hot, and soft. It flows much like a glacier does.
  • The lower mantle is extremely dense. It, too, flows.
  [Photo: Granite and Basalt]

The Core – Iron Center

About 15 percent of Earth's volume is an iron-nickel core the size of Mars.

  • The outer core is molten...and so hot it could be as fluid as water. Its motions create Earth's dynamic magnetic field.
  • The inner core is under such immense pressure that it is solid metal.
  [Photo: Granite and Basalt]

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits