First Contact (8 page)

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As practitioners of another arm of astrobiology will quickly point out, you don't have to go to Mars to get confused about whether something is alive—that is, the result of biological processes—or not. A parallel and sometimes equally intense debate has been going on for several decades about a substance found on Earth called desert varnish. Best known as the purple-black background to many ancient American Indian drawings (or petroglyphs) in the southwestern United States, the varnish coats rocks in arid climates. Nobody really knows how it gets there. Researchers have found large colonies of bacteria living beneath the very thin yet definitely layered varnish, and they have found very high concentrations of the element manganese in the coverings as well.

Living things have the property of concentrating elements in ways that nonbiological processes do not, and so the unusually high levels of manganese and sometimes iron in varnish—much higher levels than in the surrounding environment—definitely suggest biology. The opposing line of thought is that the bacteria found under the varnish have come from elsewhere and have simply found a protected place to live in very harsh
environments. As for the high concentrations of those elements not concentrated in the soil or other rocks nearby, those are the result of chemical reactions and collections of windblown dust. You would think this would be a relatively simple question to answer, but it isn't. Desert varnish thickens at an extremely slow pace, on the order of between 1 and 40 micrometers (or 0.000003937 to 0.00015748 inches) per every thousand years, so it has been impossible to experiment definitively with it in the lab. After centuries of growth, a rock's varnish covering will be about the thickness of a piece of paper. And nobody knows how or why it spreads.

As is often the case in astrobiology, the players in the desert varnish story come from a broad range of backgrounds—specialists in caves, in planetary science, in geography, in engineering. They get pulled in, not only by a desire to unravel the mystery of the origins and nature of desert varnish, but also because of some images of rocks that have come in over the years that seem to show something that looks surprisingly like desert varnish in an unexpected location: Mars. Both NASA and the National Science Foundation have funded research into desert varnish, and some years ago it was a very hot topic. The combination of painfully slow progress in understanding how the varnish grows, along with a mini-scandal in the field regarding some questionable data, has pushed it to a back burner. But that doesn't mean some intrepid souls are not still surveying the murky borderland between biological and nonbiological life.

One is Penelope Boston of the New Mexico Institute of Mining and Technology in Socorro. She is an expert in caves and the microbes that live in them, but also has a passion about both Mars and desert varnish. A woman of many enthusiasms—her department office is overflowing with alien action figures, stuffed animal bats, robots, and name tags from hundreds of conferences around the world on caving, Mars, and astrobiology—she is happiest out as a field researcher. It was while doing a five-day research expedition in the Lechuguilla limestone cave in the Carlsbad Caverns National Park, the deepest cave in the nation, that desert varnish came into her life. She was quite deep in the cave when some “fluffy”
greenish-reddish-purplish material swirling in the air fell into her eye. It didn't take long for her eye to swell shut, leading to a harrowing rope climb up and out of the cave but—more important to her—also yielding one of those “aha!” moments when it becomes clear things are not what they seem.

A trained microbiologist, Boston immediately understood that some microbes had gotten into her eye, which meant that they were living deep below the Earth's surface on what appeared to be rock face. This was before Onstott's South Africa work, so the scientific consensus was that nothing was alive in a deep cave, especially one known to be virtually locked off from the surface. Once she got outside, the swelling disappeared within four hours because, she also surmised, the microbe could not survive in the light of day. She and her colleague Chris McKay, of NASA's Ames Research Center, returned and over several years concluded that the fluffies were coming from the manganese and iron deposits in the caves, and that they were all part of a living microbial world. Driving around New Mexico, Boston constantly passed rock varnishes that featured the same manganese and iron that produced whatever had landed in her eye, and she got to thinking about what microbes might also be living in the varnish, or perhaps forming the varnish.

This encounter led to more than ten years of collecting samples of desert varnish and culturing them in her lab. The result is now a room filled with hundreds of stacked petri dishes, cylinders, and plates—some being warmed in incubators and some refrigerated—alive with what she is convinced are the bacteria responsible to a greater or lesser degree for the presence of desert varnish. The bacteria come from her home state, from Mexico, from Utah, from Chile, from volcanoes, from extreme environments of all kinds, and all are now growing in some agar medium and usually producing in bountiful quantities the purple-black signature of manganese. All started in a clear medium with tiny scrapings of bacteria added from a desert varnish sample, and most had produced massive (on desert varnish scales) amounts of the manganese-concentrating bacteria
over the years. Surrounded by so much life, however microbial it might be, Boston talks to the samples, refers to them as “these guys” or “those guys,” and says “we've got everyone in here.” She knows which are “going gangbusters” and which are struggling to survive. One she describes as resembling, under heavy magnification, a bundle of grapes. “Look at this one,” she says, pointing to a seemingly dead, crusted collection in a vial. “They look dead, but they're accustomed to desert conditions so they adapt. Rehydrate them a bit and they'll be growing fast, too.”

Has Boston proven the desert varnish is indeed a product of living organisms? Not really. As she readily acknowledges, growing the samples demonstrates that the bacteria can and do concentrate manganese as contained in desert varnish, but that lab process has limitations. To achieve a level of proof, she would have to place her samples on rocks and see how they grow, and there's the rub: They grow at such a painfully slow rate that no professor, no graduate students would still be around to detect their progress. In Death Valley, it takes varnish something like ten thousand years to grow to a thickness of one-hundredth of an inch. She has yet to settle on a plan, but she has elaborate schemes for trying to force that growth in field conditions. That's probably to be expected from a woman who once lived two weeks in a simulated Martian environment in Utah and was one of the founders in the early 1980s of what became known as the Mars Underground at the University of Colorado, Boulder. A group of students who were fascinated by the planet and wanted, in the wake of the Viking disappointments, to keep interest in it alive, they sponsored a series of conferences that attracted prominent scientists and some NASA officials. Boston dreams of being around when life is discovered there; actually, she said she would gladly fly on the maiden yearlong voyage to Mars. In the meantime, as she tries to unravel through field and lab work the barest-bones life on Earth, she is getting help from another scientific outlier.

Tom Nickles has also been lured into the borderlands of desert varnish, and he is now conducting the experiment he believes will finally determine whether living bacteria or nonliving chemicals are responsible for the coverings.
In a world of unusually bright people with unusual backgrounds, Nickles perhaps takes the cake. Tall and thin, he has wavy hair that served him well during his days as an occasional Elvis impersonator. He wears a belt with a large buffalo head buckle, which fits both his name and his locale—the University of Idaho in Moscow, Idaho. A trained engineer, former air force intelligence analyst in Turkey, test pilot trainer at Edwards Air Force Base in his beloved Mojave Desert (where he ran marathons), and so much more, he went back to school at age fifty to get a doctorate in astrobiology. There was no astrobiology program at the University of Idaho, but he found a professor who would sponsor him and he's now several years into the program. But he's hardly your typical doctoral student: He gets called in to do consulting for NASA and his plans for the desert varnish experiment looked so promising that he was invited to speak to the American Chemical Society's astrobiology panel before he even began the work.

In a stainless steel glove box with Plexiglas linings, floors, and dividers the size of a blanket chest, he had created an environment similar to the Mojave—with fans to simulate the wind, special lights to simulate the desert glare, and some extra moisture to speed up the growth process and simulate six years of varnish development in one. He divided the box in half, but both halves had a bed of sandy soil basalt and quartz as anchor for the varnish, should it grow. The two were identical except that on one side he planned to introduce some bacteria he had collected from varnish found outside Baker, California, at the Lima Lava Flow. The other side would have none of those bacteria. Would either, or both, lay down a varnish?

“Both sides start with absolutely nothing alive. The chambers have been sterilized and the substrate—the quartz and agate and basalt—have been autoclaved, so I'm sure everything will be dead. I will seal the abiotic side tight so absolutely nothing gets in, but on the other side I'll paint some of the bacteria I collected from varnish onto the rocks. Then I wait and watch. The fans will blow the dirt and dust around and the UV light will shine and the moisture will seep in and it will be just like the desert, except speeded up a bit.”

The experiment hadn't yet begun when I visited; the varnished (biotic) samples were placed in the box a few months later. Nickles didn't expect to see black rock varnish anytime soon; that takes way too long. But the bacteria, with their extra UV light and moisture, could begin the unseen varnish-making process in months, or maybe a year. That process involves one of the most important dynamics of both astrobiology and geology: Life forms interact with minerals and rocks, and transform them in minute but detectable ways. They impose a distinctly biological structure onto their nonliving surroundings, and they also can (and usually will) concentrate certain elements or minerals in the process. In the case of desert varnish, the coating is blackened by a concentrating of manganese, or can come out reddish brown if the bacteria is concentrating iron.

“The experiment will go for a year, but I'll first open up the biotic side at three months. I'll take out three specimens at random and then will put them in the antechamber,” an airtight but accessible cylinder outside the glove box. “After that comes the electron microscope to see if anything is being moved around. I'm looking for just a very crude laying down of structure, of organization, and the start of some layering. If biology plays a role in making varnish, we should start seeing [very early signs of activity] on the rock. Nothing beautiful like nice, glossy varnish forming. But something with structure.”

Or maybe not. Maybe a varnishlike coating will emerge on the side without varnish bacteria instead, giving support to the theory that the varnish is formed by chemical processes involving the wind, the sun, dust, and the surface of the rock. And by implication, any varnishlike formations on Mars would have the same nonbiological origins. All of this raises the same fundamental question: If we can't determine or define what is life on Earth, how can we possibly do it on Mars or Europa or anywhere else?

On Earth, we at least know the basic molecular, chemical, and thermodynamic outlines of carbon-based life, but we are still in something of a quandary when it comes to definitively nailing it down. That's why scientists generally focus now on the known effects of living things on rocks,
water, and atmospheres. We may not know what life is, but we have a pretty good idea of what life does—or at least the kind of carbon-based life found on Earth. What if extraterrestrial life is silicon based or has a very different way of holding and transmitting the information that produces future generations? The National Academy of Sciences formed a panel to study what came to be known as “weird life.” It met periodically from 2002 to 2005 and released a report in 2007. Not surprisingly, it complicated rather than clarified the question of what life is by offering possibilities based on silicon (instead of carbon) and replacing water as the key solvent with ammonia or methane. Science has no examples of such life, but silicon has bonding properties similar to but less adaptable than those of carbon, and life based on a solvent other than water is also considered theoretically possible by some.

In science, the most desirable and convincing proof of a finding or theory is to replicate the reaction reliably under controlled settings. So some scientists are trying to make life out of nonliving elements and compounds in their labs. It's not exactly Dr. Frankenstein redux, but close. If they can create from component parts an entity that replicates, that takes in and uses energy, and that is able to both mutate and repeat that mutation with its replicator, then they can lay claim to having achieved a proof of concept. The creation wouldn't tell us how life actually began, but it would represent a process through which life
could
have begun. And along the way, it will help define, or at least to better characterize, what life actually entails.

It's a definite competition among some twenty of the world's most innovative and admired labs, but because the task is so daunting, it is also collaborative. But none of the scientists involved is as dazzling or as excitedly eclectic in their work as Steven Benner, a chemist and molecular biologist who created and runs the nonprofit Foundation for Applied Molecular Evolution in Gainesville, Florida. He keeps afloat on grants from NASA and the NSF, but also and most importantly on the profits from the creation
of the world's first synthetic genetic system capable of producing unnatural nucleotides (the parts of DNA and RNA involved in pairing) used to monitor the levels of viruses that range from HIV to hepatitis B. With that support, he is able to push forward with efforts to produce that “self-replicating chemical system capable of Darwinian evolution” that defines life in its most broadly accepted form. With his wide-ranging knowledge and willingness to look seriously at problems from new, untried angles, he's often called on to help NASA and the National Academies of Science tackle big, complex issues; most recently, Benner was one of a handful of scientists asked by the National Academy to study the possible biochemistry of extraterrestrial life, the effort that produced the “weird life” report.