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The Four Spheres

As we move out from the centre of the Earth we pass through several sharply defined regions:

The core, consisting of liquid iron and nickel surrounding a solid inner core. The core is the origin of the Earth's magnetic field.

The mantle, consisting of dense liquid rock.

The upper mantle and the Earth's crust, together called the lithosphere. The crust is broken into giant (tectonic) plates, like pieces in a jigsaw puzzle, that float around on the upper mantle. The crust and upper mantle are together about 80 km deep.

The oceans and rivers make up the hydrosphere.

There are living things over the whole surface of the Earth, in the air, and in the ground down to depths of up to several km. There is a layer of life over the whole planet. Scientists call this the biosphere.

Covering the whole Earth to a depth of several tens of km is the atmosphere. The atmosphere helps warms the Earth by trapping the Sun's heat – this is the 'Greenhouse Effect'.

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