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rock, so it lies on top of the mantle like a layer of oil on water. The rock that forms conti- nents is lighter than basalt, so the continents “float” higher on the mantle than the rock that makes up the ocean floor. In some places, such as along the edges of the Atlantic Ocean, the ocean floor and the continental

Educational Video

For an overview of life in the ocean around Antarctica, scan here:

rock are locked together. But in other places, such as the Pacific coast of South America, the heavy basalt of the ocean floor is constantly being dragged beneath the lighter continental rock by movements within the Earth. The tectonic plates that make- up the Earth’s crust move very slowly, at just an inch a year, but as they move, they drag the ocean floors with them. In places where the mantle rock is cooling and sinking, it drags the ocean floor rock that rests on top of it down into the Earth. This creates deep ocean trenches like the 7 mile (11 km) Marianas Trench in the western Pacific. As the rocks grind their way downward, the friction causes volcanoes to erupt along the edges of the trenches. The volcanoes in Japan, Java, and the Andes mountains of South America were formed in this way. As they are pulled down at the edges, the great plates of oceanic crust move apart to form immense rifts in mid-ocean. As these rifts open, the pressure on the hot rock below is released, so it melts. Molten rock squirts up into the cold ocean

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Oceans