CLUES TO PAST, FUTURE ENCASED IN ANTARCTICA'S DEEP FREEZE : FOSSIL HUNTERS FIND EVIDENCE OF GREAT DIE-OFF.

Byline: William Mullen Chicago Tribune

The idea of giant asteroids smashing into our planet has provided the plot line to many bad movies, a recent television miniseries on the subject being no exception.

But down here, to scientists ranging about outdoors atop 90 percent of the world's ice, the idea of asteroids smashing into Earth and imperiling life as we know it is not just plausible, it is verifiable.

The deep-freeze of Antarctica, better than anywhere else, contains evidence of plant and animal life that for millions of years flourished and then abruptly, cataclysmically went extinct.

Moreover, that vast expanse of ice, scientists say, might also become the major player in a future geological cataclysm and extinction.

The most famous extinction, of course, was thought to have been caused by an asteroid that slammed into the Gulf of Mexico 65 million years ago. It killed off 75 percent of all species of life on Earth, including the dinosaurs.

What is less well known is that this was only one of five great extinctions that have occurred on Earth since life first mysteriously, miraculously appeared.

An even more lethal, if popularly ignored, extinction occurred 251 million years ago, and almost rendered the Earth a dead planet. After the so-called Permo-Triassic extinction, only 4 percent of the world's plant, animal and microorganism species survived.

Most scientists believe it was triggered not by an asteroid collision but by all of Earth's continents drifting together into a super-continent they call Pangea.

10-million-year break

Under that theory, sea levels dropped drastically after the continents joined together. In turn, the shifting plate tectonics set off immense volcanic eruptions in Siberia, spewing enormous clouds of dust into the atmosphere that effectively smothered most of life on Earth.

Whatever the cause, in the aftermath, the atmosphere remained so noxious, it took 10 million years for widespread biological diversity to rebloom.

``The world just went to hell at that moment,'' said Gregory Rettalack, a University of Oregon paleogeologist specializing in fossil soils. ``We almost lost (all life) at that time. Everything says the (Permo-Triassic) extinction was very abrupt.''

He is one of a small group of scientists who, since the 1950s, has been going to Antarctica looking at the fossilized evidence of past climatic changes in hopes of getting clues about future ones.

Specifically, they are studying the ominous trend of global warming and the possibility that it could eventually melt Antarctica's ice. Evidence of past such occurrences there show how resulting rising sea levels could trigger Earth's next great die-off, exterminating many forms of life in the sea and on land.

Since the cold engulfed Antarctica at the beginning of the last ice age, 30 million years ago, it has been virtually untouched by most forms of life. Certainly the only human inhabitants have been a tiny trickle of visiting explorers and scientists over the past 100 years.

The size of the United States and Mexico combined, Antarctica holds 70 percent of the world's fresh water. All of it is frozen, in places up to three miles deep.

Most of it is ancient ice, having neither flowed nor fallen for millions of years. If it were spread evenly around the globe, the ice would encase the world in a shell 164 feet thick.

Now it is beginning to melt, and it is the relentless expansion of the human race, a recent, ice age species, that is the main culprit in this global warming, scientists say.

If current warming trends were sufficient to melt it all, it would raise worldwide ocean sea levels by an estimated 60 to 180 feet. That would inundate some of the most populous areas on Earth, including Florida, the Mississippi Delta region and Bangladesh.

Such a flood might be catastrophic for Whumans. For the planet, however, it would be more like a return to normalcy. For about 90 percent of the time in the past 570 million years, Earth has been a warmer place and its polar regions have been ice free.

Normally, Antarctica is a warm, lush, living place. There is abundant evidence of this in the rock and soil. Unfortunately, most of that rock and soil is deeply buried by ancient ice.

Seeking answers in Antarctica

Scientists scour Antarctic rock and soil for clues to Earth's long-term climatological cycles and clues to how such changes might affect life today. They have to make do with the mere 2 percent of the vast continent that lies uncovered. Most of what they can get at is rugged mountain peaks and crests poking through the ice cover.

Most recently, they worked from a tented base camp atop the Shackleton Glacier, a slow and mighty ice river cutting through the Transantarctic Mountains to the Ross Sea.

Using helicopters, they established even more remote field camps around rock faces in a 200-square-mile area along the glacier.

Nearly all of them were Antarctic veterans, members of a loose scientific consortium that has been organizing paleontological expeditions down there since the 1950s.

The most fruitful expeditions have been at various sites along the spectacular Transantarctic Mountain chain.

Finding rock of different ages, then finding fossils inside the rock, they painstakingly follow the progress of plant and animal species over millions of years. When the fossil trail stops suddenly, replaced by new life forms, they know they have encountered an extinction.

The first dinosaur bones ever found in Antarctica came out of the Transantarctics in 1991. William Hammer of Rock Island's Augustana College cemented his name in paleontological history with that find.

The bones he pulled out, the remains of two enormous beasts that once roamed warm, humid Antarctic savanna, eventually will go to Chicago's Field Museum of Natural History.

EWdith and Tom Taylor, University of Kansas paleobotanists, have located whole petrified forests in the mountains, some from dinosaur times, some from times before dinosaurs. The stumps stood upright just as they grew when the world was warmer, and fossilized fallen leaves laid about like stony ground litter.

Rettalack, Hammer, the Taylors and others of the Antarctic paleontological group were eager to dig in the rock around Shackleton Glacier, much of it almost perfectly bracketing the Permo-Triassic extinction.

There are abundant 251-million-year-old deposits there bearing fossils of thriving plant communities that soon were to be annihilated in the extinction.

Other deposits are 240 million years old. The fossils they bear show new life forms that finally rebloomed more than 10 million years later. These new arrays of plants, animals and microorganisms ruled the world for 12 million years, only to disappear with the rise of the dinosaurs 228 million years ago.

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Photo

Photo: William Hammer's paleontological expedition team takes measurements in the Transantarctica Mountains.

Knight-Ridder Tribune Photo Service