## Crusty continents

Imagine that you're riding on something a bit larger - say a continent like Australia. (You really don't have to imagine it, because this is actually what you are doing as you read this book - being taken for a ride on a continent. Every morning when you get out of bed, you and your bed have moved a tiny bit during the night.) For the last 40 million years, the Australian landmass has been moving steadily northwards, at about the same speed that your hair grows - about 10 centimetres a year. Perhaps one way to work out how far we've travelled is to never cut your hair (except that it wouldn't be too popular with your parents). If your hair had never been cut, you could measure how far you'd gone since you were born. In 40 million years Australia has travelled more than 2000 kilometres from Antarctica, to which we were once joined.

Since I was born, Australia has travelled about 5 metres. How far has it gone since you were born?

Australia isn't the only continent that's doing this. They all are - sliding around the globe, like bumper cars in very slow motion, or like a herd of elephants randomly sliding on their bums across a frozen lake. Every so often they bump into each other. They can do this because the hard rock that makes the continents is semi-floating on a layer of molten rock that is almost liquid (something like porridge). The hard rock on top is called the continental crust. I know this makes it sound like some kind of bread, but that's really what it's called.

India, for example, is pushing into Asia. And the more it tries to shove its way north, the higher the Himalayas get. As with the bumper cars, the only way to go is up.

Imagine you have a carpet on a shiny wooden floor. If you run hard until you land on the carpet, you'll go sliding along the floor. When the carpet hits the wall it will rumple up into folds, like a very small mountain range. (Better not try this one, because you and the wall could collide quite hard!)

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