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Editor's Note: This article is an extended version of "Bugs in the Ice Sheet" from the May 2012 Issue of Scientific American.
BOZEMAN, Mont.—Locked in frozen vaults on Antarctica and Greenland, a lost world of ancient creatures awaits another chance at life. Like a time-capsule from the distant past, the polar ice sheets offer a glimpse of tiny organisms that may have been trapped there longer than modern humans have walked the planet, biding their time until conditions change and set them free again.
With that ice melting at an alarming rate, those conditions could soon be at hand. Masses of bacteria and other microbes – some of which the world hasn't seen since the Middle Pleistocene, a previous period of major climate change about 750,000 years ago – will make their way back into the environment.
Once thought to be too harsh and inhospitable to support any living thing, the ice sheets are now known to be a gigantic reservoir of microbial life. Altogether, the biomass of microbial cells in and beneath the ice sheet may amount to more than 1,000 times that of all the humans on Earth.
Internment in the ice amounts to an evolutionary strategy for microorganisms: preserving genetic blueprints by storing them in deep–freeze for a future re-entry, said John Priscu, a Montana State University professor and pioneer in the study of Antarctic microbiology.
"It's a way of recycling genomes," he said. "You put something on the surface of the ice and a million years later it comes back out."
'Storehouse for genes'
Priscu has spent the past 28 Austral summers on the southernmost continent, studying what he calls "the bugs in the ice sheet." Antarctica has the oldest ice on Earth; parts of its glacial landscape date back about a million years, and some pockets are believed to be up to 8 million years old. "There's a lot of history in that ice sheet," said Priscu.
Much of that history appears to still be alive. Priscu has found living bacteria in cores of 420,000-year-old ice and gotten them to grow in his laboratory. Other researchers report bringing far older bacteria back to life.
The ice allows microbes to enjoy a sort of immortality, preserving ancient genetic material and allowing creatures that have long disappeared from the planet to someday return. "That's what's interesting about the ice – it can serve as a storehouse for those genes," said Jonathan Klassen, an evolutionary biologist and postdoctoral research fellow at the University of Wisconsin, Madison. "Things that went extinct have the possibility of coming back."
Could this be Jurassic Park on Ice? Not likely, scientists say. The only things able to survive in these cold, dark, crushed quarters with little to eat or drink are microscopic organisms, and most of what has been found appears related to microbes from other cold and icy environments.
Still, with heat-trapping greenhouse gases warming the polar regions much faster than the rest of the planet today, investigators have many questions about the bugs in the ice sheet. Researchers are trying to determine how these organisms can survive such a brutal habitat, some seeming to sit in what resembles a state of suspended animation for millennia. The findings could point the way for the discovery of life in other extreme climates, such as frozen planets and moons.
The more immediate concerns sit here on Earth. Cells and carbon dumped out of melting glaciers could turn into huge piles of decomposing organic matter – compost – that generate carbon dioxide and methane as they decay, a potentially significant source of greenhouse gas emissions that climate researchers have yet to consider.