Our Changing Planet

Revision cards on C1 Chapter 7 of AQA GCSE Chemistry

Structure of the Earth

Key Points

  • The Earth consists of a series of layers. Starting from the surface we have the crust, the mantle then the core in the centre. A thin layer of gases called the atmosphere surronds the Earth.
  • The Earth limited resources come from its crust, the oceans and the atmosphere.


About 80% of the air in our atmospher lies within 10km of the surface.


The average thickness of the crust is about 6km under the oceans about 35km under continental areas.


Starts underneath crustand continues to about 3000km below the earths surface. Behaves like a solid but is able to flow very slowly.


Radius of about 3500km. Made of nickel and iron. Outer core is liquid, inner core solid.

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Structure of the Earth Diagram


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The restless earth

Key points 

  • The earths crust and upper mantle is cracked into a number of massive pieces (tectonic plates) which are constantly moving slowly.
  • The motion of the tectonic plates is caused by convection currents in the mantle, due to radioactive decay.
  • Earthquakes and volcanoes happen where tectonic plates meet. It is difficult to know when the plate may slip past each other. This makes it difficult to predict accurately when and where earthquakes will happen.
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The distribution of volcanoes and earthquakes


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The Earth's atmosphere in the past

Key Points

  • The earths early atmosphere was formed by volcanic activity.
  • It probably consisted mainly of carbon dioxide. There may also have been water vapour together with traces of methane and ammonia.
  • As plants spread over the earth, the levels of oxygen in the atmosphere increased.

Oxygen in the atmosphere

Carbon dioxide + water  energy from sunlight sugar + oxygen 

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Life On Earth

Key Points 

  • One theory states that the compounds needed for life on earth came from reaction involving hydrocarbons, such as methane and ammonia. The energy required for the reaction could have been provided by lightning.
  • All the theories about how life started on earth are unproven. We can't be sure about the events that resulted in the first life-forms on Earth.
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The amount of gases in the atmosphere today


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Gases in the Atmosphere

Key Points 

  • The main gases in the earths atmosphere are oxygen and nitrogen.
  • About 80% of the atmosphere is nitrogen and 20% is oxygen.
  • The main gases in the air can be seperated by fractional distillation. These gases are used in industry as useful raw materials.
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Carbon dioxide in the Atmosphere

Key Points 

  • Carbon moves into and out of the atmosphere due to plants, animals, the oceans and rocks.
  • The amount of carbon dioxide in the earths early atmosphere has risen in the recent past largely due to the amount of fossil fuels we now burn.
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The Carbon Cycle


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