The Antarctic Connection

By ANDREW PURVIS

Antarctica has long been viewed as the remotest of continents, buried beneath millions of tons of snow and ice, miles from its nearest neighbor, and "doomed by nature . . . never once to feel the warmth of the sun's rays," in the words of 18th century explorer Captain James Cook. Even scientists studying the way the earth looked hundreds of millions of years ago have tended to ignore this solitary landmass. So it came as a surprise to many researchers last week when a pair of American geologists reported that Antarctica may not always have been so distant. In fact, about 570 million years ago, the scientists estimate, today's South Pole was probably less than a thousand miles from the future site of Las Vegas.

The theory, presented at a meeting of the Geological Society of America in San Francisco, is the first to offer a plausible scenario for when and where the continents drifted during this critical period in the planet's history, just as life was beginning to emerge from the sea. It may help explain the birth of the Pacific Ocean, and even point the way to valuable mineral deposits. Said co-author Ian Dalziel, from the University of Texas at Austin: "The theory gives us a new road map for the past 570 million years."

Geologists have long known that 250 million years ago the continents were bunched together in a massive protocontinent, dubbed Pangea. They have also had convincing evidence -- from the geochemical makeup of rocks at the continents' boundaries -- that this was not the first supercontinent in the earth's history. But the shape of that earlier supercontinent remained mysterious.

Last week's report, delivered by Dalziel and his colleague Eldridge Moores of the University of California at Davis, revealed a key piece of new evidence. On the shore of the Weddell Sea in Antarctica, the scientists had tentatively identified an ancient rock formation known as the Grenville Belt, which runs from northern Canada along the eastern seaboard and then dips out of sight in southwestern Texas. This geologic connection, combined with some data from the magnetic orientation of ancient rocks, suggests that Antarctica, as well as Australia, was shoved up against the western coast of North America late in the Precambrian period (from 1 billion to 570 million years ago) as part of the original supercontinent, said Dalziel.

The new geography could shed light on several geologic mysteries. Researchers have not yet agreed on the origin of the Pacific Ocean. Some have suggested it was formed when Siberia split off from North America; a few even postulated it was created by the moon calving off from the earth long ago. In the new scenario, the ocean would have been created when Antarctica and Australia migrated away from North America 570 million years ago.

This chronology would also help explain the dawning of life on land, which occurred around the same time. The breakup of a supercontinent such as this one, scientists believe, would trigger massive flooding of the continents and the creation of shallow coastal waters -- exactly the kind of spawning ground from which sea creatures first emerged and adapted to life on the shore.

Some geologists, including Paul Hoffman, a research scientist at the Geological Survey of Canada, believe that the new map could point the way to valuable mineral discoveries. If the theory proves correct, silver, copper and zinc (all found in eastern Australia) should also turn up in northwestern Canada. But scientists caution that before anybody rushes out with a prospector's pick, research must confirm that the rocks in the Western U.S. are really related to those in eastern Antarctica. Dalziel estimates that this comparison should take no more than six months -- a short wait to clear up a mystery that has been around for half a billion years.