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Physical Environment > Causes of Ice Ages |
This site tells the story of the history of the universe. Click Earlier and Later to follow the story. Note: Many facts have been simplified to make them easier to understand. |
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We are not sure why ice ages begin and end, although there are many theories. One theory says it is the effect of continental drift which starts them. Ice ages always seem to happen when there are mountains on the Earth, created by the collisions between continents, as there are now. How could continental drift cause an ice age?
When continental drift creates mountains, or when a continent drifts over a pole, then snow starts to fall. Snow reflects the Sun's heat back into space, so cooling the Earth. The ice also weathers the rocks, so minerals are washed out of them and carried by rivers to the sea. Here the minerals join with carbon dioxide from the air. The amount of carbon dioxide in the air is reduced so the greenhouse effect is reduced and the Earth cools still further. Moving continents also change the flow of water from one ocean to another and mountains affect the winds. So in many ways continental drift affects the climate. Eventually continental drift separates the continents, weathering wears down the mountains, and the climate goes back to its normal warm state. If continental drift happens in cycles, that would explain why ice ages seem to occur every 250 million years or so. Another theory notes that sometimes in history there were mountains without an ice age. Perhaps changes outside the Earth also played a part in starting ice ages. Changes in the Sun or its movement round the Galaxy might have lessened the sunlight reaching the Earth. It takes about 250 million years for the Sun to travel once round the Galaxy. Coincidence? |
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Physical Environment > Causes of Ice Ages |
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