Coral reefs have been on the planet for over 400 million years!

Coral reef are made up of a ton of calcium carbonate which is basically limestone. This calcium carbonate is secreted over thousands of years by billions of tiny soft bodied animals called coral polyps. All this secretion builds up over millions of years to create beautiful coral reefs. These reefs provide important habitat, giving homes to 25% of the planet’s marine species.

http://www.sciencedaily.com/releases/2007/05/070515074933.htm

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