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Unit 4. The Earth

The Earth has different layers or spheres: geosphere, hydrosphere and atmosphere.

The geosphere is the solid part of the Earth. Part of it lies under the oceans and makes up the ocean floor. Part of it emerges and forms continents and islands. There is an anormous amount of energy in the interior of the Earth. This energy is so great that it can break the crust of the Earth, cause mountain chains to emerge, earthquakes and volcanic eruptions. That energy has changed the shape of the geosphere in the last millions of years.

The hydrosphere is all the water on Earth. It can be solid, liquid or gas.

The atmosphere is the layer of air which surrounds the Earth. It extends for hundreds of kilometres and is essential for life on Earth.

Weather, living organisms and other factors change the surface of the Earth. Over time, rocks wear down and break apart. This natural process is called weathering.

There are three types of rocks, depending on how they are formed: igneous, sedimentary and metamorphic.

The rock cycle is a set of processes which forms and changes rocks over thousands or millions of years.

Earthquakes

They are strong movements of the earth´s crust caused by a sudden release of energy from beneath the surface.

Volcanoes

Volcanoes are openings in the Earth´s crust where magma comes to the surface (lava). 

There are three types of volcanoes: active, dormant and extinct.