Jenean Greenler, age 11, of Tulsa, Okra., for her question:
Where are the coral islands made?
The corals that build reefs and islands enjoy life in tepid waters. Other corals can live in the cool waters of the North Atlantic and same types can endure life in the chilly fiords of Norway. But the best builders of the coral family must live in shallow tropical seas where the water is always above 70 degrees Fahrenheit.
Traces of coral reefs and ridges have begin found along the icy shores of the Arctic. These traces tell us that these waters were once tropical. Other fossil records tell us that magnolias once roamed in Alaska and crocodiles once thrived in warm waters of the Dakotas. The world's climate has changed and those warm weather plants and animals have taken up residence nearer the equator.
Wherever we find coral islands, reefs and rides the climate is tropical or was tropical in some remote time. In recent geological times the coral builders have lived in shallow waters within the belt of the trade winds. Most of our coral reefs and islands are within Latitudes 30 degrees north and south of the equator.
The coral builders are also busy around Bermuda, slightly north of these waters. Here the Gulf Stream and the warm Sargasso Sea provide them with the right kind of living conditions. Them are no coral builders along the western shores of Africa and South America within the trade wino belts. This is because these shores are washed by cold ocean currents.
The coral islands of the Pacific and the Great Barrier Reef of Australia all lie within the trade wind belt. There is coral‑making along the shores of Florida. In the remote past a massive platform of coral was built in this region, you see lumps of cord rock beside the roads and canals through the Everglades. There the very land on which trees and grasses now grow was built by corals.
The Great Barrier Reef of Australia is still a building. It lips off shore, stretching for a distance of over 1,000 miles. At low tide a jagged floor of beautiful coral formations appears above the surface.
The coral islands of the warm Pacific arc, called atolls. Many of them are built on old volcanoes. When a volcanic cone appeared above the water it formed a round island. Baby corals, swimming in the sea, settled on its shores and started to build their stony apartment houses. In time the pounding waves washed down the volcanic peak. But the beaches were firmly cemented with coral rock.
For this reason an atoll is often a circle of land enclosing a central lagoon. Sometimes there is a break in the circle and the coral island is a moon‑shaped crescent. These atolls may occur wherever the trade winds warm the Pacific. Other coral building goes on in the warm Indian Ocean and off the balmy West Indies.