Our Changing Planet

Our Changing Planet

1. Structure of the Earth

   • The Earth is made of layers called the core, mantle and crust with the atmosphere around the outside.
   • The Earth's limited resources come from its crust, the oceans and the atmosphere.

2. The Restless Earth

   • The Earth's crust and upper mantle is cracked into tectonic plates which are constantly moving.
   • The tectonic plates move because of convection currents in the mantle that are caused by radioactive decay.
   • Earthquakes and volcanoes happen where tectonic plates meet, but it is difficult to predict accurately when and where earthquakes will happen.
   • Wegener's theory of continental drift was not accepted for many years.

3. The Earth's Atmosphere in the Past

   • The Earth's 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.

4. Life on Earth

   • One theory states that the compounds needed came from reactions involving hydrocarbons and ammonia with lightning providing energy.
   • All the theories about how life started on Earth are unproven and so we cannot be sure how life began.

5. Gases in the Atmosphere

   • Most of the carbon dioxide in the early atmosphere became locked up in sedimentary rocks.
   • About four-fifths (almost 80%) of the atmosphere is nitrogen, and about one-fifth (just over 20%) is oxygen.
   • The main gases in the air can be separated by fractional distillation. These gases are used in industry as raw materials.

6. Carbon Dioxide in the Atmosphere

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