Coral reefs and coral islands hold secrets about the age of the earth. They can tell us about the shaping of our oceans and the continents. They can also challenge catastrophism since they seem to have developed slowly over a long period of time.
Coral reefs consist of a hard core covered by living organisms that are able to resist the ocean’s wave action. Reefs are one of the most complex marine ecosystems in the world. Reefs are constructed of both trapped sediments and the organisms that live on them.
In the fossil record, reefs appear to suggest long periods of stability. But did fossil reefs form the same way current reefs do?
How Reefs Form
Reefs can form in two ways. They can either grow slowly in one place until they reach full size, or they can be formed relatively quickly by transported sediments. If a reef is formed by transported sediments, the coral could have grown elsewhere in pieces and been transported by water movement to its current position. This movement would likely have occurred during a global flood. 
Fossil reefs show evidence that they were formed by transported sediments. The diverse organisms found in fossil reefs are in a specific orientation that would not happen if the organisms had all grown together in one location.
The transportation process would not have taken millions of years. Fossil reefs such as the Nubrigyn Algal Reefs in eastern Australia are now seen as the result of massive flows of sediments. The pre-Flood reefs were broken up and washed away by the Flood, then deposited in layers we can see in the fossil record.
These recycled reefs show that the ocean floor was ripped up and warped during the Flood, in order to pour water over the continents. Then, the reverse would have occurred as the water drained off the land, forming the ocean basins we see today.
The question of how long this process took can be answered by both living coral reefs and dead coral islands. Read how the speed of reef growth supports the theory of catastrophism.
Updated March 2010.