Ice's age? More than 8 million years.

A piece of a glacier buried under a layer of volcanic ash in East Antarctica has lain undisturbed for at least 8.1 million years, says an international team of scientists. The presence of the ancient ice lends support to the theory that the East Antarctic ice sheet, which includes the bulk of the South Pole's ice, has stayed much the same for the past 15 million years--frozen and barren.

Not all geologists agree, however. Some believe that the frozen continent we now know had trees, vegetation, and much less ice as recently as 3 million years ago, during the Pliocene epoch. To them, the discovery does not rule out the possibility of a dynamic East Antarctic ice sheet before that time, with some areas melting and refreezing several times over the ages.

Earth was about 3oC warmer during the Pliocene, so determining what Antarctica looked like then can help scientists predict how global warming might affect the ice sheet in the future. If the East Antarctic ice sheet melted, it would raise the global sea level 60 meters, enough to submerge many coastal cities.

The new research, published in the Aug. 3 Nature by David E. Sugden of the University of Edinburgh, George H. Denton of the University of Maine in Orono, and several others, fuels this spirited debate over the stability of the coldest continent on Earth.

The team established the age of the ice by dating the layer of ash on top. By comparing the abundances of different isotopes of argon trapped in the ash particles, they determined that the ash settled into a crack on top of the glacier during the Miocene epoch, several million years before the Pliocene.

The ash showed no signs of disturbance by wind or moisture. "There's no other mechanism we can think of to get glacier ice underneath," Sugden says. "We argue that the ice has been there at least as long."

The ice's longevity, the group says, supports the idea of a polar climate persisting in Antarctica right through the Pliocene.

David Harwood of the University of Nebraska at Lincoln, however, offers a different interpretation. The presence of the ancient ice may signify "selective preservation," a local phenomenon that needn't apply to the entire continent. "I'm sure there was ice in Antarctica 8 million years ago," he says. "If you're trying to take evidence from any particular area. . .and apply it for all of Antarctica, that's a bit dangerous."

Harwood and Peter Webb of Ohio State University in Columbus have argued that the East Antarctic ice sheet fluctuated in size up until the Pliocene. High up in the mountains, they have found tiny marine fossils called diatoms. These creatures must have lived, 2 to 3 million years ago, in watery basins deep in the heart of the continent. Glaciers later carried them up and deposited them at a high elevation.

Most experts agree on the present stability of the East Antarctic ice sheet but disagree on its sensitivity to a global warming of a few degrees. "It's so cold that all you do by raising the temperature is to increase the amount of water vapor in the atmosphere and therefore the amount of snow," Sugden says. "And it still doesn't melt."

Harwood, on the other hand, emphasizes the insulating property of the frozen ocean surrounding the continent, which keeps it very cold and dry. "With a 3o warming of ocean temperature, that would cause at least a 15o to 18o warming of mean annual temperatures on the continent. So if you warm the oceans a little bit and remove the sea ice, then the atmosphere would warm significantly."

Although Harwood applauds the accurate dating of this one piece of ice, he says that resolving the larger debate will need "lots of little bits of information like this."