A half-billion years ago, it was a chain of volcano islands adrift in a tropical sea. Over untold millenia, it took new forms, like a lump of clay forever being reshaped.Three hundred million years ago, the place that would become Long Island was a dinosaur swampland at the edge of a towering mountain range cast up by the slow-motion collision of continents. And just 20,000 years ago, it was a wasteland of woolly mammoths and iceberg lakes in the menacing shadow of a retreating glacier as tall as a skyscraper and as wide as a continent. But not until 11,000 years ago -- an eyeblink in the 4.6-billion-year life of Planet Earth -- did the rising sea finally encircle a fish-shaped pile of sand pushed together by the newly departed ice sheet.In geological terms, Long Island was born yesterday.
