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Professor Iain Stewart explains how the temperature of the earth is affected by its orbit round the sun, and the tilt of its axis. This was a theory put forward by James Croll. Professor Stewart draws the changing orbit of the earth around the sun on a sandy beach. He explains why this causes temperatures to fall and how this can be exaggerated by the changing tilt of the earth.
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First broadcast:
14 December 2010

Classroom Ideas

Show pupils photos of vast areas of the world covered in ice. Tell students that there are have been times in Earth's history when much of the Earth was covered by ice. Can be used to introduce the theories of why glacial periods happen. Ask pupils to then draw a diagram and explain what is shown on the clip.

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