Geologists find coral atolls as fascinating as detective stories. The clues lie strung through the earth's warm seas in festoons of ringlike islands, like Wake Island in the Pacific (see cut). And for more than a century the geologists have been debating what the clues really mean. The most familiar theory is that atolls started as coral reefs fringing a small island. When the island sank (or the sea rose), the ring of coral kept growing upward, eventually forming an atoll with a lagoon where the island used to be.
In the latest American...
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