Our Changing Planet

Structure of the Earth
1. The Earth is made of layers called the core, mantle and crust with the atmosphere around the outside.
2. The Earth's limited resources come from its crust, the oceans and the atmosphere.
The Restless Earth
1. The Earth's crust and upper mantle is cracked into tectonic plates which are constantly moving.
2. The tectonic plates move because of convection currents in the mantle that are caused by radioactive decay.
3. Earthquakes and volcanoes happen where tectonic plates meet, but it is difficult to predict accurately when and where earthquakes will happen.
4. Wegener's theory of continental drift was not accepted for many years.
The Earth's Atmosphere in the Past
1. The Earth's early atmosphere was formed by volcanic activity.
2. It probably consisted mainly of carbon dioxide. There may also have been water vapour together with traces of methane and ammonia.
3. As plants spread over the Earth, the levels of oxygen in the atmosphere increased.
Life on Earth
1. One theory states that the compounds needed came from reactions involving hydrocarbons and ammonia with lightning providing energy.
2. All the theories about how life started on Earth are unproven and so we cannot be sure how life began.
Gases in the Atmosphere
1. Most of the carbon dioxide in the early atmosphere became locked up in sedimentary rocks.
2. About four-fifths (almost 80%) of the atmosphere is nitrogen, and about one-fifth (just over 20%) is oxygen.
3. The main gases in the air can be separated by fractional distillation. These gases are used in industry as raw materials.
Carbon Dioxide in the Atmosphere
1. Carbon moves into and out of the atmosphere due to plants, animals, the oceans and rocks.
2. 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.

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