Radiometric dating corals
Nor have we taken into account the time necessary to form the volcanic base on which the reef grew.
Recently, further calculations for the rate of reef growth have been based on the concentration of dissolved calcium carbonate in seawater and upon the rate at which corals can absorb it and manufacture their shells.
During periods of volcanic inactivity, corals and lime-secreting algae colonize the areas just below the shoreline around the volcano.
In this way a reef can be built that is several thousand feet tall, even though living corals can only survive in the upper layers of the ocean.
The most reasonable explanation for coral growth begins with a volcano.
Volcanoes can build themselves thousands of feet upward from the ocean floor, and some of them will grow tall enough to break through the surface of the water.
This last item is particularly important because the rate of growth of coral depends on the amount of dissolved calcium carbonate it can extract from the seawater.
Calcium carbonate, though, is rather insoluble, so there is not a large concentration of it in ocean water.