The Great Barrier Reef is the largest structure ever built by a living organism. At least 350 different coral species can be found on the reef, which is 2,000 kilometers long and forms a natural breakwater for the east coast of Australia.
The underlying sediments, twice as old as the reef itself, indicate that the region was once above sea level. The reef began to grow more than 25 million years ago. As this photo shows, the "global" reef consists of many unconnected individual reefs, separated by deep water channels.
The calcareous remains of corals provide the basic building material for the reefs, while coral algae residues provide the cement that holds this structure together. When fossilized, these reefs and the eroded remains of them form thick blocks of limestone.
The causes of its size and longevity are the great geological stability of the settlement on the Australian platform and the favorable ocean currents. Coral cannot exist at temperatures below 21 ° Celsius. The warmth of Australian waters varies little with depth due to the beneficial action of the southeast winds. These winds blow over the outer edge of the reef for nine months a year, and this also maintains the supply of seawater rich in organic material necessary for coral growth.
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