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Zero's the high. The lake is a cracked, frozen slab. But all through the Antarctic winter, cells have been biding their time. If life survives on Mars, it could be like this.

Antarctica, the Dry-Valley Lakes region. It gets no warmer than zero degrees Celsius here. Lake Bonney is completely frozen on top. Even when summer begins, in November, the melting amounts to just some slush and a few small holes in the surface of the lake.

But a little water is all it takes to revive the "freeze-dried" life that hibernates all winter, buried in more than six feet of ice. Here, tiny organisms live in "one of the coldest, most inhospitable environments on earth," says Hans Paerl, professor of marine sciences.

For the past two years, Paerl and Jay Pinckney, research assistant professor of marine sciences, have traveled to Lake Bonney to study these "bugs." Learning exactly what these organisms are and how they survive, Paerl says, might reveal how life could exist on Mars or other frozen planets.

Paerl first heard of the life at Lake Bonney from John Priscu, a friend and professor at Montana State University who had been drilling through the ice to study the water beneath. This water contains minerals and salt accumulated over thousands of years of erosion and glacial movement.

"Each year the glaciers melt ever so little," Paerl says, and tiny streams creep underneath the ice. The resulting water layer is ten times as salty as sea water, which is why it doesn't freeze.

Finding life in this mineral-rich water was one thing—discovering it in the ice layer was quite another. Priscu and Paerl were intrigued by the prospect of anything surviving in the "moonscape, desert-like environment" around the surface of the lake. It's called the Dry Valleys because it never rains, and the surrounding mountains shield it from snow. It's one of the few places where you can see exposed soil.

The soil is where the bugs get their start. In summer, the ice on the lake melts slightly and gets "rubbery in places," Paerl says, forming pockets and holes. Winds are high here, so some of the dirt blows onto the lake and accumulates in the cracks. The dark clumps absorb sunlight and gradually melt their way down through the ice, taking the bugs with them.

Viewing one of these clumps, or aggregates, under a microscope reveals "a lot of life," Paerl says. Molecular analysis shows that each aggregate contains a "microcolony" made up of a variety of microbes, including bacteria and blue-green algae. The scientists wondered how this relatively complex community developed from a simple particle of soil.

They found that when each clump of soil melts its way down into the ice, it heats up just enough to surround itself with a small pocket of water, forming "a liquid microcosm in a frozen world," as Paerl calls it. "If in fact there are microorganisms on Mars," he says, "they may very well be able to use this type of localized solar heating to generate water."

At Lake Bonney, the trickle that collects around each aggregate is enough to wake the bugs from their dormant state, called cryptobiosis. Almost immediately, they start the business of their life—making their own energy through photosynthesis. In the lab, the scientists have been able to "turn on" photosynthesis within minutes by melting the ice around the bugs, Paerl says. "It's like instant life."

To stay alive, the bugs need nutrients. Phosphorus and iron they get from the soil. But nitrogen is harder to come by because the usual sources, such as rain or run-off, don't exist at Lake Bonney. The scientists suspected that at least some members of the microbial community were "fixing" nitrogen, which means converting nitrogen from the air into a usable form. Their hunch was right. Using a microscope, they could see that the blue-green algae were made up of tiny cells called filaments, which look like a chain of beads. They recognized these cells as the kind that can fix nitrogen.

As the organisms grow, they reach out to microbes on other aggregates and glue themselves together. "The soil particles that blow onto the ice are very simple," Paerl says, but as the bugs start photosynthesizing and fixing nitrogen, small groups link themselves into bigger ones. Then the chance for melting water is greater, and the microbes can get more nutrients and perform more complex biological processes. "We're learning a lot about how simple life can easily evolve into a more complex community," Paerl says.

This kind of algae, also called cyanobacteria, is one of the simplest known microorganisms, Paerl explains. "They were here on earth two billion years ago, before there was any complex life. We might call them primitive, but in fact they're the only ones that can really tolerate these extreme conditions."

Now the scientists are figuring out whether these nitrogen fixers are run-of-the-mill, or something never before discovered. Researchers in Paerl's lab have sequenced the nitrogen-fixing genes of these algae. Now the automated DNA sequencing facility at Carolina is searching for a match among known organisms.

Ordinary or not, these microbes represent what Paerl calls "life at the edge."

"When you get beyond these lakes, there's no more life. That's it," he says.

On his last trip, Paerl did find the mummified carcasses of two seals. "They came up from the Ross Ice Shelf during the winter, I guess, and got lost." With no food or water in sight, they couldn't have survived long.

The researchers survive with the help of cold-weather survival training and some serious outdoor gear. Their "labs" are three small huts, and they eat and socialize in a hut that's heated by the propane stove used for cooking. But they do their sleeping in one-man tents pitched on the edge of the icy lake. At night it gets down to 30 below. "You get used to the cold," Paerl says. "Once you get in that sleeping bag, it's not bad."

And of course, when the research is done, the scientists board a helicopter and fly toward home and more civilized conditions. Only the bugs remain at Lake Bonney, waiting for summer and their chance to grow.

Hans Paerl and Jay Pinckney, faculty at the Institute for Marine Sciences in the College of Arts and Sciences, conducted this research as part of a team with scientists from Montana State University, Oregon State University, and the National Aeronautics and Space Administration (NASA). The work is sponsored by the National Science Foundation and NASA.