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Great Barrier Reef
The Great Barrier Reef is the world's longest group of coral reefs.
A coral reef is a type of underwater environment. It is shaped by structures made of a kind of rock called limestone.
The Great Barrier Reef is made up of more than 3,000 individual reefs. These reefs extend about 1,400 miles (2,300 kilometers) along the northeast coast of Australia.
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Great Barrier Reef
Ocean animals called corals form the limestone structures of coral reefs. Coral is a stony substance made up of the skeletons of marine (water) animals called polyps <<PAWL ihps>>. As corals grow, they make limestone skeletons. When corals die, their skeletons build up and become cemented together to form reefs.
A coral reef looks like a colorful sea garden. The Great Barrier Reef has about 400 kinds of polyps of many shapes and colors. The reef supports a rich variety of sea life, including such animals as sea birds and brightly colored fish. It is also home to a variety of plants.
The Great Barrier Reef began to form millions of years ago. But drops in sea level during ice ages have interrupted the reef's growth many times. About 14,000 years ago, the level of the oceans was lower than it is today, and the reef was above water. About 6,000 years ago, the oceans reached their current level, and corals returned to shallow coastal areas. The waters around the Great Barrier Reef are warm all year long. Many people visit the reef to enjoy its beauty and its warm waters.