by Marc Kaufman
Christner has made five trips to Antarctica between 2000 and 2009 searching for life in ice. Scientists like Christner especially love the McMurdo Dry Valleys of Antarctica because of its many extremes: It’s a two-thousand-square-mile region of snowless, gravelly valleys on a continent otherwise covered in white, it has liquid lakes hidden beneath deep coatings of ice, scores of glaciers, and winds of up to two hundred miles per hour. Not that long ago, the region was considered to be devoid of life. Now teams go down looking for, and finding, all kinds of microscopic organisms. It’s also a mecca for scientists and engineers preparing for the day when Americans (or others) will need to know how to operate, and what to look for, in the environments likely to be found on Mars and elsewhere beyond Earth. Just a few miles from the ICIBASE camp, a NASA-sponsored team was continuing its long-term research with technology they hope will one day travel to Jupiter’s moon Europa and be used to explore the enormous liquid ocean known to lie beneath its thick crust of ice and suspected to have conditions suitable for life.
Making the LSU research station anywhere near as frigid as where the ice came from requires heavy-duty condensers, compressors, and fans and results in a constant hissing sound—adding to an already surreal disconnect between inside the room and out. It’s a small place that combines the feel of an operating theater and a meat locker, minus the hanging carcasses. Here ice is the star.
An ICIBASE alumnus hauled out three thirty-pound blocks from the storage room, each from a different part of McMurdo’s Taylor Glacier, and placed them on a light box. One was clear, though full of captured, cartoonish bubbles; another had thin layers of sediment that produced an elegant, soft layered effect that could have come from a potter’s hand. The last sample came from the bottom, where the glacier—a river of ice—grinds the rock below and mixes with it. Christner was most interested in the second sample, the one with the thin layers of sediment.
“We can melt the ice and bring the microbes out—they’re alive, we know this,” he said, gesturing to the block on the light box. “We can also take a natural ice sample from Taylor Glacier and measure the gas concentrations, and I can tell you in a piece of ice like this they make no sense at all. The level of CO2 is [three thousand] times what it is in the atmosphere now, so something caused it to increase. That value couldn’t possibly be atmospheric from earlier days because it’s way too high. Oxygen is normally twenty percent of the total gas in ice, exactly like in the atmosphere. But in this area of our sample, the O2 depleted. So you have CO2 increasing and oxygen decreasing—it’s a classic signature cellular respiration.”
Okay, the microbes may be respiring (breathing, if you will) in the ice, but how could they possibly reproduce and keep their community from disappearing? That takes far more activity than these organisms could seemingly muster in their barely liquid, very salty ice vein habitats. Christner had an answer, one based on measurements of the rate at which microbes, living in ice at 5 degrees Fahrenheit, can build the genes needed to successfully divide and create a new organism. “There’s a misunderstanding about microbes, that they’re always dividing. But like humans, they’re not reproducing all the time at all in nature. Okay, these guys are extreme—they may divide once in two hundred years. Just do the math: We know that some cold-adapted bacteria can synthesize about one hundred base pairs of DNA per day. But they have a genome with about three million base pairs, so it takes a while—not the kind of project a grad student would want to start up and ever expect to finish. Time means nothing to microbes. It’s all about maintenance, just keeping alive.”
When ice from the latest expedition arrives, the room will have more than 1,500 kilograms of ice that could contain something on the order of 15 billion microbes—all in some stage of “living,” but nonetheless frozen in ice.
Pulling that precious ice from deep inside the Taylor Glacier was quite an operation, one that required two years of planning, a fair amount of equipment, and the help of National Science Foundation helicopters. It was frigid and windy when the team arrived at their site, nearby Lake Bonney, and set up camp. Each day they hiked a mile up to the face of the glacier and got to work. Using chain saws, demolition hammers, and ice picks, the group had to first build an ice stairway up about thirty feet from the base of the glacier. Then, over a week, they dug a tunnel more than forty feet into the ice—pulling out more than fifty tons via banana sleds. Above the tunnel was another hundred feet of ice, and picking the wrong spot to dig could lead to a catastrophic cave-in. That’s why Christner and Skidmore helicoptered out from the American base at McMurdo Station and spent four hours intently surveying the glacier’s ice face, looking for a spot without any telltale signs of surface weakness or calving.
The ICIBASE team—five men and two women—took turns with the equipment, each cutting and drilling until they were coated in ice chips and dust, and looking rather crazed. But the chain saw work was generally considered plum, because inside the glacier they were protected from the cutting winds that froze the haulers and lookouts on guard for teammates in distress, with windchill temperatures down to –40 Fahrenheit. At the end of their ice alley, the team studied the frozen walls for unusual and differing traits, and cut and drilled and yanked out slabs of up to one hundred pounds, for transport back to Louisiana and Montana for study. Two years before, they’d had to donkey-haul their catch out of the tunnel and through a boot-grabbing mudslide because the glacier had begun its yearly melt early, and a waist-high river had quickly formed between their ice castle and dry ground. This year they arrived sooner so they could finish the tunnel and airlift out the blocks before the melt river appeared.
The goal of the mission was to determine whether microbes in the ice constitute an archive of dead or metabolically inactive organisms, or if they formed a living, interacting community. Previous work in Antarctica had identified seemingly active biochemistry—the presence of by-product carbon dioxide and nitrous oxide with distinctively life-produced signatures, akin to the gases ICIBASE had found in the Taylor Glacier ice—and raised the prospect of finding microbes with clearly identifiable forms and functions. In other words, Christner and a handful of others are working to prove the hypothesis that Antarctic ice, as well as glacial ice elsewhere, is not lifeless and unchanging but rather an ecosystem no different from a forest or stream. It’s clearly an extreme, slow-moving, and spare environment, but it’s a world that supports certain kinds of similarly constructed life just the same—organisms with the kind of antifreeze found in some cold-water fish, organisms that appear to depend on the biochemistry performed by other nearby organisms for their survival, organisms with an ability to withstand extreme desiccation and intense radiation. That trait is essential, since scientists assume they initially blew down to Antarctica from the oceans or other continents, withstanding long, harsh periods in the atmosphere. The definitive research has not been done yet that would prove glacial microbes are conducting the work of “life” in the ice—as opposed to what they do when they’re brought into the lab, fed, and warmed up a bit, and begin to move around—but the logic of the argument is getting stronger with each expedition.
And how extreme can their Antarctic living conditions get? Russian and American researchers, including Christner, have identified signs of life almost three miles below the surface in ice that originates from liquid Lake Vostok, the largest of the recently discovered subglacial lakes on the continent. That’s nearing halfway up Mount Everest if you’re going in the other direction. A high, windswept plateau of East Antarctica, the surface of Vostok is often described as the coldest place on Earth. The irony is that the deeper the drill goes into the ice above Lake Vostok, the more likely that they’ll find living microbes. The reason is that it gets warmer deep down in the glacier, and finally warm enough under the ice that Lake Vostok (roughly the size of Lake Ontario) stays liquid all the time. The weight and pressure of the glacier clearly are part of the reason why, but Russian scientists—who have worked at Vostok since the
mid-1950s—believe geothermal hot spots under the lake may be spitting out heat and gases as well.
Russian scientists and engineers are scheduled to make their long-delayed piercing of the pristine lake in 2011, bringing up what will be the first Vostok water ever touched by humans. Astrobiologists and Antarctica specialists are torn—eager to know what might be living in the waters, but worried that the Russian drill and collection device will contaminate the lake. While Vostok is the largest subglacial lake in Antarctica, there are hundreds of others. One of them, Lake Bonney in West Antarctica, has already been explored and mapped by a NASA-sponsored mission headed by Peter Doran of the University of Illinois in Chicago and underwater-robot maker Bill Stone, one of the breed of out-of-the-box engineers drawn to the same challenges and questions as Christner and other scientists. Without men like Stone to design, calibrate, and operate robots and machines that allow scientists to make finds in the most inhospitable parts of Earth, the most revelatory astrobiology expeditions would never have gotten off the ground.
Tall and lanky, Stone is a grown-up version of the science geek who had a better chemistry lab in his basement than his high school did. When he was still in school, his mom suggested he join a club to meet other kids. Not knowing what it was, he chose spelunking. Some decades later he is still a caver, leading extreme expeditions into the deepest caves on Earth: weeks of rappelling into the dark, swimming through narrow water tunnels, sleeping well below the surface on ledges and outcrops sometimes never before visited, and then climbing back up sheer cliffs. When not caving, Stone runs Stone Aerospace outside Austin, where the Lake Bonney robot was conceived and assembled.
Doran and Stone’s Lake Bonney robot logged 250 hours under the ice and traveled more than thirty-five miles to conduct the first sophisticated, 3-D exploration of a polar lake, one covered in about ten feet of ice. The Volkswagen-sized “Bot” was also a test of concept: Could a submersible robot be programmed to not only follow a preset path, but also to independently explore areas where something unusual appeared? During two seasons under the ice the Bot, with the help of forty-five computers, performed as hoped.
But the real prize is hundreds of millions of miles away, on Jupiter’s moon Europa. Beneath miles of ice, Europa is home to a giant ocean sixty miles deep and with twice as much water as the oceans of Earth—a prime target for astrobiologists. A joint NASA-ESA mission to Europa is now in the works for the 2020s, a scouting party preparing for the day when the moon’s ice cover will be broken and a much smaller and more sophisticated bot than Lake Bonney’s will be inserted into the waters below. A liquid ocean, even if it’s kept dark by miles of ice, is the kind of place where life just might exist; in fact, we know it does exist right here on Earth.
Back in Baton Rouge, Christner might as well be in a different galaxy. He favors shorts and loud shirts—an azure Hawaiian shirt the day we met—and still puzzles about exactly how he became an ice man. His early great interest, what brought him into microbiology and then astrobiology, was thermophiles—the extreme organisms that live in and around hot springs, deep ocean vents, and the outer reaches of volcanoes. On schematics of the tree of life, many thermophiles can be found at the very bottom, leading some scientists to speculate they were the earliest or at least among the earliest life forms on Earth.
“Yes, I wanted to study thermophiles for my doctoral thesis,” Christner said, and laughed. But instead he went into the microbes-in-ice field, in part because his mentor at Ohio State University had a collaboration with another team that had a large collection of ice cores from around the world. “They had ice from the Andes, from Tibet, Greenland, and Antarctica; and it was a huge opportunity. But to tell the truth, I thought when I was done I would write up the findings and move on to something else. My assumption was based on the conventional wisdom of the time that any microbes in there were just hanging out in the ice, doing nothing. We could learn about the past from them, but nobody thought about anything beyond that. Bottom line, that’s not at all what we found. We found things alive in the oldest ice, seven hundred and fifty thousand years old. Some were spores, but some were not and seemed to be doing things, especially the ones near dust and sediment.”
His tentative hypothesis had been that glacial ice is generally not a reservoir for dead or hibernating microbes, but is instead an environment with a complex and extensive living ecology of its own. Five trips to Antarctica later, he is increasingly confident that this is true. In fact, based on what he acknowledges is very limited data collected from two drilling holes, he believes Antarctica—which contains about 70 percent of the fresh water in the world—may well sustain a world of microbial life that exceeds in mass all the life found in all the freshwater rivers and lakes of the world combined. In samples from the Vostok ice core, almost three miles down, Christner isolated a bacterium that produces a protein that may well help the organism to survive, in part by altering the freezing and recrystallizing of the nearby ice—directing the potentially destructive processes away from the organism. In other words, their survival advantage appears to have come from a molecular adaptation that allowed the microbes to change their frozen environment enough to make life possible.
That kind of remarkable ability to inhabit such a harsh environment, and to even seemingly transform it, is why Christner assumes microbes will one day be found on Mars and elsewhere. “Based on what we’re learning on Earth, I can’t see that microbes living on Mars would be such a big jump. I mean, the conditions they live in here are in some ways just as severe, yet they’ve adapted. Not only that, we believe that ice is a habitat for life—providing a liquid environment under otherwise frozen conditions. Waste from one microbe is food for another, so it is likely that microbes are interacting and cooperating to extract every usable bit of energy. Almost all the water we see in the solar system is in an ice form, and I don’t see why some of that ice wouldn’t have microbial life, too.”
It’s that kind of leap of the imagination that has people like Christner looking deep inside the Earth to see life in the beyond. To enter, explore, and ultimately understand the world of microbial extremophiles, you need to be, inside your head, something of a human extremophile yourself.
3 WHAT MAKES SOMETHING ALIVE?
What is life? Even though an answer has been passed on to generations of biology students, they weren’t getting the full story. When scientists invented the modern field of astrobiology, they had to wrestle with a fundamental problem: There is no scientific consensus about precisely what makes something alive. Given that unsettling absence, did it really make sense for astrobiologists to apply to the rest of the universe the never-quite-exact definitions we had come up with on Earth? To make matters all the more confounding, what would be a sure signature of biology on our planet could be totally nonbiological on Mars, and vice versa. So how do you find life in the beyond if you can’t agree on what life is on Earth?
Because it’s in the business of trying to find “life” beyond Earth, NASA has probably done more to try to define it than any other organization. Here is an unofficial working definition: Life is “a self-sustaining chemical system with the capacity to evolve in a Darwinian manner.” The definition came out of a workshop of biologists, physicists, and chemists in 1994, and it does meet many of the basic criteria scientists and others are looking for. Broadly, it accounts for the known constants of life on Earth. All living organisms take in some form of energy, use and change it, and then release it as waste; all use the same twenty amino acids to construct the proteins that make that and all other activity possible; and all use RNA and DNA molecules to store genetic information and to construct proteins. The Darwinian evolution comes directly and inevitably from the presence of DNA, since all DNA mutates.
But the definition has many critics, some of whom think it is not only incorrect but also misguided. The criticisms come from many directions: those who argue the definition would rule out viruses, prions (which cause “mad cow” disease), and ot
her seemingly “living” organisms; those who want to base any definition on a specific capability such as metabolism or reproduction or the enclosing of a cell nucleus by a cell wall; those who think in the more abstract terms of a physicist and want a definition that takes their discipline (the Second Law of Thermodynamics, for one) into account. Relying on that law, the Austrian quantum physicist Erwin Schrödinger famously suggested that life—in its broadest terms—be defined as something that avoids immediate decay into “entropy,” the chaotic and then utterly uniform state the entire universe will someday revert to since all structure has in it the seeds of its own falling apart. Living things, Schrödinger proposed in his 1944 book, What is Life?, postpone this inevitable process by taking in nutrients and turning them into energy; at death the life forms eventually succumb to the force of entropy and break down so the atoms of the once-living body become evenly distributed again, recycled by the Earth.