Review Darwin's Classification of Coral Reefs

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Coral reefs are composed of calcium carbonate deposited by corals and other animals and plants.  By definition a reef is a rigid, wave-resistant structure, and thus can form "instant rock" which becomes part of the world's coastlines.  Broken fragment of coral can also pile up to form low islands composed of carbonate sand.

Among many other accomplishments, Charles Darwin was the first scientist to develop a systematic explanation for the patterns of coral reef development he observed during his voyage on the HMS Beagle during the 1830s.  Darwin reasoned that reef-building corals would continue to build reefs upward toward the sunlight even if the bedrock below was sinking.  As long as the rate of subsidence of the bedrock was equal to or lower than the growth rate of the corals, a coral reef could maintain its position in the ocean for thousands of years.

Based on your reading and lecture notes, what are the three stages of the development of a reef recognized by Darwin?

1.
2.
3.

What types of reefs are illustrated by Tupai and Bora Bora?

Tupai:

Bora Bora:

What is the name for body of water at the tip of the arrow marked A?

What type of rock is the island at the tip of the arrow marked B made of?

If a drilling rig were constructed at the tip of the arrow marked A, and a borehole was drilled 3000 meters into the earth, what type of rock would you expect to find at the bottom of the borehole?  Explain the reason for your answer.

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