Chemistry: Changes in the Earth and its atmosphere

The Earth's crust

The Earth has a layered structure: crust, mantle and core. The crust and upper mantle are cracked into large pieces called tectonic plates which move slowly but can cause earthquakes and volcanoes where they meet. 

Main layers:

• Crust: relatively thin and rocky
• Mantle: has the properties of a solid but can move very slowly
• Core: made from liquid nickel and iron

The Earth's atmosphere surrounds the Earth. 

Tectonic plates

They are constantly moving at a few centimetres per year. Although it doesn't sound like much, over millions of years the movement allows whole continents to shift thousands of kilometres apart, which is called continental drift. 

The plates move because of convection currents in the Earth's mantle. These are driven by the heat caused by the natural decay of radioactive elements in the Earth. 

Where tectonic plates move, the Earth's crust becomes unstable as the plates push together or ride under or over each other. Earthquakes and volcanic eruptions happen at the boundaries between plates and the crust may 'crumple' to form mountain ranges. 

There are two main types of tectonic plates:

• Oceanic plates occur under the oceans (denser than continental plates and are pushed down under continental plates if they meet)
• Continental plates form the land

Volcanic activity

Where tectonic plates meet, the Earth's crust becomes unstable as the plates slide past each other, push against each other or ride under or over…