9781422283691

 Volcanoes erupt and the Earth shakes where the plates of the crust meet. On the Edge

The plates of the Earth's crust are moving apart under the oceans. For example, on the floor of the Atlantic, one plate (carrying South America) is moving towards the west, while the other (carrying Africa) is moving east. This is called sea-floor spreading . As the two plates move apart, molten rock wells up from below to fill the gap and becomes part of the spreading plates. The boundary between spreading plates is called a constructive margin because new plate material is being created.

Black smokers Along the mid-ocean ridges hot water escapes from the seabed. It is often colored black by dark minerals. The black streams look like spirals of smoke, and are called black smokers. Strange life forms exist around black smokers, including sulphur–eating bacteria, worms, and prawns.

∆ In mid-ocean, molten rock from below wells up and makes new plate material. At the ocean edges, plates descend and are destroyed.

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