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Looking for Life in All the Wrong Places

Microbes from the least hospitable places on Earth, could seed the universe with life.

By Will Hively
May 1, 1997 5:00 AMNov 12, 2019 6:15 AM


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When Imre Friedmann and his wife, Roseli Ocampo-Friedmann, settled down in Tallahassee following years of academic wandering, they fell into a comfortable evening routine. After he returned home from Florida State University and she from Florida A&M;, they kept track of world-shaking events by watching the cbs evening news, usually while eating dinner. This began in the fall of 1968. Day after day, year after year, they watched and they munched. One night in 1978, they heard anchorman Walter Cronkite talking about Mars--out of the blue, the possibility of life on Mars, in the form of algae, or bacteria, that could live inside rocks. Ah! Roseli gasped, her utensils losing their grip on some now- forgotten meal. He’s talking about us!

Two obscure microbiologists who had published a paper about bacteria living in the remotest reaches on Earth--Cronkite was indeed talking about them. The news item, it turned out, was a sequel to a major story of a year and a half earlier. On July 20, 1976, the Viking 1 spacecraft had touched down on Mars, and the Friedmanns, along with millions of other Americans, had listened to Cronkite describe the historic landing. Over the next few months the evening news followed the progress of Viking experiments designed to test the Martian soil for signs of life. The probe discovered unexpected compounds, some of which could have been produced by microorganisms. But mission biologists eventually concluded that the soil on Mars was sterile: no life, they said, could survive the combination of ultraviolet solar radiation, extreme dryness, and lethally oxidizing compounds found on the planet’s surface.

Not long after Viking landed on Mars, the Friedmanns published a paper describing microorganisms living in the Ross Desert of Antarctica, in mountain ranges so cold and dry they were thought to be devoid of life. NASA had sent researchers to test soil there, in fact, as a trial run for Viking; they found nothing persuasive. But the Friedmanns did, without leaving Tallahassee. Not in the soil, but in a rock shipped to their lab-- a small but perfect specimen of Beacon sandstone, as Friedmann described it. The rock was colonized by bacteria that led a miserable existence. All through the dark polar winter, they would barely hold on, at 50 below. Not until summer could they thaw, rehydrate, and photosynthesize, and then only when midday temperatures were sufficiently high--and only if, at the same time, water from melted snow still lingered. The Friedmanns called these creatures cryptoendoliths: crypto for hidden, endolith, meaning inside rocks.

The Friedmanns’ article came out on September 24, 1976, in the midst of the Viking season on Mars. At that date, newspapers were still marveling at the marginally positive evidence for life in a scoopful of Martian soil taken aboard the spacecraft, and here were a pair of researchers announcing life discovered on Earth. I am telling you, Friedmann says, it went totally unnoticed.

A year passed, and the excitement about Viking had soared and crashed. And then one day Friedmann got a phone call. NASA and the National Science Foundation wanted to know if they could issue a press release on his work. He wondered what had prompted these agencies to discover cryptoendoliths; by then, both NASA and the nsf had been funding his research for several years. I said, ‘Okay, go ahead,’ Friedmann recalls. We didn’t know what a press release really meant.

What it meant was that Walter Cronkite would talk about the Friedmanns as they ate dinner. Suddenly cryptoendoliths were planetary news. The timing, Friedmann later realized, made sense. After the disappointing results from Viking, Friedmann’s rock-bound organisms could raise hope anew for finding life on Mars. Microbes might have escaped the hostile surface environment by holing up inside rocks--and NASA scientists would now know where to find them. That evening, after the news broadcast, the phone began ringing. We were inundated by telephone calls from the world press, says Friedmann. And we were in every newspaper in the world, practically.

The calls turned out to be Friedmann’s 15 minutes of fame. By the early 1980s no other spacecraft had gone to Mars and Martian biology had become a sitting duck for congressional budget cutters. The search for life on Mars--not only funded research but the very subject, Friedmann says--became a no-no. Yet Earth biology was fine, and his own work on endoliths continued, supported quietly by both NASA and the nsf. Over the years Friedmann has searched for, and found, life in the most unpromising environments on Earth, and his discoveries have profound relevance to the search for life beyond our own planet. But so far the lightning bolt of instant fame has not struck twice.

The fickleness of publicity hasn’t mattered much to Friedmann. Now 75, he has long been adept at hunkering down for the long haul--a human echo of his microbial subjects. As he describes his career, he speaks softly for the most part, most softly when he recalls the painful episodes. His vaguely European accent is Hungarian, a relic of his childhood in Budapest. As a boy, he wanted to be a scientist, but he liked too many subjects to specialize. Eventually he settled on botany, with an idea that the fieldwork would take him to isolated, exotic places. A small, heavily used espresso machine in one corner of his lab hints of the next phase in his career, graduate work in Vienna shortly after World War II.

At the moment, the espresso machine is seeing a lot more action than the equipment set up to study bacteria recently brought back from Siberia. They are formidable survivors. Buried in permafrost, they’ve been doing practically nothing for 3 million years, so little that standard tests would detect no signs of life. Surprisingly, the microbes thrive best not in Siberian ice but at room temperature. They would rather be basking in the Florida sun, but back home they bide away epochs underground, at around 15 degrees below zero with no sunlight, no air, no fresh food. They don’t like it, Friedmann says, rather to the point. They should, in fact, shrivel and die. And yet hunkered down as they are, they might conceivably outlast such trifling interludes as ice ages.

Friedmann keeps a large collection of such death-defying organisms in his lab and studies them between treks to exotic environments. Over the course of his career he has become a connoisseur of extreme habitats--the worst on Earth.

If you think you know what extreme means, think again. Friedmann has been mulling the concept for decades. It is not easy to define an extreme environment, he says. It is simply different from ours-- what we ourselves do not like. Among the denizens of the extreme are thermophiles that love water so hot it would kill us, psychrophiles that thrive in places so cold, halophiles in salt brine so strong, and barophiles under pressure so high that we’d expire. Together, such microbes are sometimes called extremophiles, as opposed to mesophiles--creatures, like us, that prefer medium conditions. Of course, from an extremophile’s point of view, we are the ones who live at extremes. It is a very subjective measure of things, Friedmann says.

Yet there are absolutes: life has its limits. There is just so hot that chemistry can go, just so cold that processes like photosynthesis can occur; they become too slow. But right at the limits, some microbes carry on by the skin of their teeth, barely surviving, rarely reproducing. In this limbo, says Friedmann, this gray zone between the limit of adaptability and actual death, there are organisms that live permanently-- always hungry, always too cold. Generations and generations live there. They are pushed beyond what any extremophile could possibly like, almost to the absolute limits of existence. In human terms, Friedmann says, you could compare them to the most miserably living generations of pariahs in India. They are born, they live, and they die in the gutter. And these organisms exist on Earth.

Friedmann has traveled the world looking for them, but the wretched of Earth do not congregate in places that humans find comfortable. So Friedmann has searched in deserts from the Gobi in Mongolia to the Atacama in Chile, and in frozen lands from pole to pole. He has looked high on mountains, and deep in the sea. And along the way, he has wondered: If microbes colonize such miserable habitats on Earth, where else beyond Earth might similar life-forms exist?

Friedmann’s search began when he moved to Jerusalem. From the time I joined the Hebrew University in 1951, he says, I was determined to find algae in the Negev Desert. As a botanist he had studied seaweed, a large form of algae, but in the desert he would settle for single-celled species. I had the idea that maybe algae adapted to desert conditions, Friedmann says. People thought it an outlandish idea, slightly crazy. So he wandered the Negev for a decade, looking in all the wrong places--which is to say, in the desert soil. Finally in 1961 a friend, an oil geologist, brought him a piece of limestone with a green substance inside. The geologist thought the green coloring was some form of copper, but chemists said it was not. Perhaps, he suggested, it is something biological. Friedmann could hardly believe his eyes. He scraped off a sample, whisked it to the nearest microscope, and saw algae.

Porous rock, Friedmann soon realized, is a better habitat for a microbe than parched desert soil. A rock can store water in its pores, and because it is often translucent, it can admit sunlight, allowing photosynthesis, yet filtering the extremes of strong light that kill microorganisms in the desert.

Once he knew where to look, Friedmann found endoliths everywhere. These mountains, he says, pointing to a photograph of the Negev on his wall, look absolutely barren. Indeed, as you scan it you see no trees or shrubs, not a blade of grass, not even a lichenous rock. It looks as dead as, say, the surface of Mars. But inside, the hills are practically covered by a green layer. Only a millimeter beneath the hard, rocky surface, he found, the desert slopes were alive. For ten years he had been that close.

Friedmann was not actually the first to discover endoliths; they had been found in the Alps as early as 1914, but the discovery had been safely buried in the scientific literature. Initially, however, his colleagues were not excited by Friedmann’s attempts to revive the study of this strange form of life. His first presentation on the Negev algae, at the International Botanical Congress in Edinburgh in 1964, drew less than overwhelming attention, he says. His first manuscript on desert algae got the same So what? response. It was rejected on submission but finally published, in 1967.

Meanwhile Friedmann, Roseli, and a series of loyal graduate students were doggedly breaking open rocks in apparently lifeless places and finding life. By the late sixties, they knew that in hot deserts, at least, more photosynthesis occurs inside rocks than in soil. I thought that in Antarctica also, we should look for algae inside rocks, Friedmann says. By then NASA was using Antarctica as a training ground for Mars probes, and NASA researchers were probing Antarctic soil for microorganisms. Friedmann argued that microbes would have retreated inside rocks on Mars too, if life had ever existed on that planet. Nobody wanted to believe me, he says. No one, that is, but a single Antarctic researcher.

Friedmann wanted very badly to go to Antarctica, to extend the range of his endolith studies, but he could not get funding. Solid rock was not considered a prime hunting ground for life. However, in 1973 he befriended a microbiologist named Wolf Vishniac who was a leading scientist on the Viking mission. Friedmann showed him colonized rocks from the Negev, and Vishniac soon agreed to look for similar rocks on his next trip to Antarctica.

In the Antarctic summer of 1973 Vishniac set up a remote camp with one other researcher, a geologist. That’s a very small group, Friedmann says. One of the basic rules in Antarctica is that you never go anywhere alone. But two was still okay. The researchers had picked a mountainous area with steep, hanging valleys, a rough, windy place where Vishniac was burying microscope slides in the soil, hoping to catch microbes. He went to retrieve these slides, and he left the geologist in the tent, Friedmann says. He went alone. He told the geologist when he would return. Six hours after that stated time, Vishniac still hadn’t returned, and his partner called McMurdo Station for a rescue team. They eventually found Vishniac’s frozen body at the bottom of a deep precipice, where he had apparently fallen. Who knows? Friedmann asks. Who knows why?

Word of the accident reached the Friedmanns in January 1974. I absolutely despaired, Friedmann says softly. He mourned for his friend, and at that point, he says, I gave up. Friedmann would simply have to pursue some other line of research; going to Antarctica to find endoliths was out of the question.

Two months later, Friedmann received a letter from Vishniac’s widow, Helen. We have received from Antarctica a collection of rocks and soil samples, including some rocks thought to contain algae, which I believe Wolf collected for you, she wrote. I shall be glad that at least this part of Wolf’s work will not be wasted.

The entire paper Friedmann subsequently published in 1976 was based on just one of those rocks, a piece of sandstone about two inches in diameter. (At the time, the organisms were thought to be single-celled algae, but they have since been recognized as photosynthesizing cyanobacteria.) On the strength of his preliminary findings, Friedmann was able to begin regular expeditions to Antarctica in 1976. A year and a half later, after Walter Cronkite described his discovery, Friedmann squirmed briefly in the limelight, explaining his findings to everyone who called. Today a thick scrapbook filled with yellowed newspaper clippings from that time sits high on a shelf in his office.

As far as his own research went, the stories were reasonably accurate: he had shown that the microbes were certainly alive, although at that point he knew almost nothing about how they managed to survive in frozen rock. But the stories also suggested, wrongly, that such microbes could still be alive on Mars today. In fact the Martian atmosphere vanished almost completely billions of years ago, along with liquid water on the surface, and the climate over most of the planet became colder than Antarctica. Cryptoendoliths may once have lived on Mars, but they would now be long gone. Yet if Mars ever did have life on its surface, Friedmann suggested 20 years ago, the last foothold was inside rocks. And so it is a possibility that we can find fossils inside rocks--fossils of microorganisms, which were the last to disappear.

In 1996 they reappeared. Fossils, or something at least resembling fossilized microbes, were discovered in Martian meteorites that landed in Antarctica. I do not, at this point, have a strong opinion about the microorganism-like structures, says Friedmann. But given the intense debate now blossoming over the meteorites, Friedmann points out that Antarctic rocks bearing definite microfossils would be the best analogues to Martian ones, since they would probably have formed under the same conditions.

Endoliths have been joined in recent years by a number of other impossible life-forms, microbes that might also be models of life on other planets and moons. Earth is infected with bacteria more than a mile below its surface--the current record for deep-dwelling life is 9,600 feet. Microbes may live deeper, but drilling to find them is too difficult and expensive. In some deep habitats the organisms have no access to organic food; they seem to survive on carbonate compounds in the rocks themselves. Meanwhile deep-sea thermophiles have been found near vents at temperatures as high as 230 degrees. Mars or planets beyond may have underground water, perhaps geothermally heated and thus suitable for these types of organisms. Another kind of deep habitat may exist on Europa, one of Jupiter’s moons, which is covered by a frozen ocean. Water may be sloshing beneath this ice, warmed by the friction of strong Jovian tides.

Yet another extraterrestrial model could be provided by the microbes from Siberian permafrost that Friedmann is now studying. Permafrost begins as living tundra soil. During the brief summers the top portion of soil thaws and, as fresh silt arrives, the lower portion is buried. When soil layers sink too deep for summer heat to reach them, they become permanently frozen, as far down as 3,000 feet. And in those very old, frozen soils, Friedmann says, there are living microorganisms. Microbes that thrive at the surface end up being carried down to layers lost in an eternal dark chill. After finding them in Siberia, Friedmann’s team drilled into the even colder permafrost of Antarctica and again found living bacteria in large numbers. They were not inactive or dormant, like the frozen cultures commonly kept in research labs; they were somehow carrying on with life.

Could something similar have happened on Mars? While liquid water may or may not exist deep inside Mars, the planet certainly has ice. The north pole is covered by it, and researchers believe that permafrost soil undergirds much if not all of Mars. Perhaps life has been entombed there as well. One hitch is that Martian permafrost temperatures average about 100 degrees below zero, which is quite a bit colder than the -16 degree soils that Friedmann probed in Antarctica. Another hitch is that such microbes would be required to survive 3 billion years rather than 3 million. Still, Friedmann thinks they might have left fossils behind.

All these facts about Mars--along with new data about other worlds in our solar system and beyond--have restored the excitement to exobiology. But for Friedmann, facts about Earth have always come first. Distant planets inspire speculation, but so does the one planet where, for now, we can check hunches about where to find life against nature’s actual results. And when the search gets down to microbes, much of Earth remains unexplored. I do believe it is better to work on terrestrial samples, Friedmann says. Which are real. Which are here.

Cryptoendoliths are indisputably here. And to understand them truly, Friedmann must study them in their natural environment. His Antarctic trips--17 so far--typically start from McMurdo Station. Helicopters fly research groups over range after range of snowy mountains into a frozen wilderness--to Friedmann, one of the most beautiful landscapes on Earth. They set up camp with tents and small stoves for cooking but no heat. Preserving food is no problem; it stays frozen. For several weeks, team members make observations, look for colonies of microbes, and set up instruments to record data until the next team returns, usually the following year. In Antarctica, Friedmann says, everything takes longer. On a windy day, you try not to expose much skin; your blood might never reclaim it. On a relatively mild day, you might remove a glove to fiddle with an instrument until your fingers numb.

Friedmann is usually happy to finish 75 percent of the work at hand--and even that requires careful preparation. You have to plan ahead, he says, and order everything in the summer for next year. In the intense cold, plastic often breaks, and metal parts freeze. If you set up an instrument to record data, come back the next year, and find that something went wrong, you’ve lost two years of research, he points out: when no data are recorded, it takes the next year to diagnose the problem, get new parts, and return to Antarctica to make repairs.

At first, Friedmann set up his data-gathering procedures like a space mission; he had no choice. Solar-powered instruments, with cumbersome lead-acid batteries for backup, transmitted data from his remote research sites to a polar-orbiting satellite; a French tracking station downloaded the data in Toulouse. All this, he says, was extremely expensive. Now we have very small data loggers--they are a little bigger than a shoe box-- that have incredible memory; they are very cheap. Once a year we have to retrieve the data; we go there and exchange the memory. A lithium battery in these small sealed boxes provides all the power needed to preserve the data for seven years. Thanks to these data loggers, we have continuous recordings of climates in the millimeter range. Friedmann, his students, and colleagues set up these devices in the Gobi, Atacama, and Negev Deserts. Their data, Friedmann adds, are unique: surely no one else has bothered to monitor the health of our planet’s far-flung rocks so closely for so long. From Antarctica, Friedmann boasts, we have the best measurements from one single rock, the experimental rock--six years of continuous measurements.

The subject of all this attention looks almost comical--a boulder of soft brown sandstone the size of a coffee table, with sensors embedded in it every few millimeters. A spaghetti of colored wires connects them to the data logger, like a human patient hooked up to monitors. Every five minutes the apparatus measures factors such as light intensity, the presence or absence of water and snow, temperature, and humidity.

With such thorough field observations, plus experiments in the lab, Friedmann’s research teams have figured out the endoliths’ productivity--the crop yield inside rocks, so to speak--with great accuracy. Much of the carbon they photosynthesize is lost. Some of it has to be bound up in proteins the bacteria produce to fight off encroaching ice crystals; the proteins then leak out of their membranes. In the end, the microbes are .025 percent efficient, retaining only 3 milligrams of carbon per square meter per year--a crumb. After all their labors, they have little capacity left over for growth.

All in all, it’s a rotten life. These organisms live, really, in the limbo between life and death, Friedmann says. So precious is the summer sunlight that they must use it ready or not. If the wind tips a rock to a different angle, it can be curtains for microbes who get slightly more shade. As rocks weather and flake, a type of erosion provoked largely by the organisms themselves, the exposed microbes have to creep deeper into the rock.

What goes on in permafrost is not nearly so well understood. Friedmann and Lisa Rivkina, a geomicrobiologist at the Russian Academy of Sciences, have begun some key experiments. To keep the microbes extracted from permafrost as uncomfortable in his lab as they are in Siberia, Friedmann bought unusual, expensive incubators. They look a little like bread-baking machines, but they chill rather than warm the specimens, keeping temperature constant to a hundredth of a degree. Results come in so slowly, on a timescale more geo than bio, that Rivkina has gone home for six months.

Friedmann wants to know how such ordinary bacteria manage to live in such an extraordinary environment. Bacteria forced into subfreezing habitats usually become dormant: they slow their metabolic activity to a very low level. Years later, many can revive if thawed. But not after millions of years.

Even if frozen, Friedmann says, microorganisms cannot survive forever. Radiation--either from radioactivity in rock or from cosmic rays falling from the sky--will damage bacterial DNA and over millions of years will almost certainly kill a microbe. Another risk involves changes in the structure of amino acids, a kind of spontaneous twisting known as racemization. Amino acids can exist in either left- or right-twisting versions, but living cells use only left-twisting ones. If a cell becomes completely dormant, it cannot repair proteins that spontaneously flip to the right-twisted form, and these harmful errors can build up. After 3 million years, a revived bacterium would find itself with proteins that no longer function.

So there must be present, even at permafrost temperatures, a very low level of metabolic process, at least to take care of DNA repair and to replace old amino acids, Friedmann argues. The accepted way to measure metabolism is to add a radioactive form of carbon to a culture of microbes and measure how much they incorporate after incubating a few hours. At the temperatures of permafrost, however, it would take many months for the bacteria to ingest detectable amounts. Friedmann’s group solved the problem by investing in the kind of expensive, highly sensitive carbon 14 detector that archeologists use for carbon dating. It sits on a lab bench most of the time, until the bacteria accumulate enough carbon 14- -and then the fancy tool earns its keep. It shows that even at -4 degrees, the bacteria still have a metabolism.

Metabolism also requires water, a scarce commodity at such temperatures. Liquid water is present, Friedmann explains, because permafrost is not solid ice. A film of water that adheres to the surface of soil particles resists crystallization. There is a very thin layer of unfrozen water, and apparently it is enough, he says. Sipping on water spread on specks of dirt buried under shells of ice, these bacteria carry on their desperate, life-sustaining chemistry. They do little more than repair damage from racemization and radiation. Rather than reproduce, they simply linger while ice ages rush by and mountains dwindle.

The more Fried-mann studied extreme habitats, the more a familiar microbial face kept turning up--a type of cyanobacteria named Chroococcidiopsis. It flourished when Friedmann reared it at room temperature in his Florida lab, yet in nature it almost never colonized mild habitats, and it even avoided the extreme conditions that extremophiles enjoy. By suffering beyond the extremes, it seemed to be looking for a place where it could be left alone.

Chroococcidiopsis was among the first to show up in the Negev; it was also the first organism the Friedmanns isolated from Wolf Vishniac’s Antarctic rock. In rocks from Ellesmere Island in the Arctic Ocean, near the opposite pole, Friedmann found it again. Chroococcidiopsis turned up in hot deserts in Africa, Australia, California, Mexico, and Asia. In the Italian Alps, the Rockies, mountains all over world, Friedmann found it again at these windswept summits. If you see anything else alive, that environment is too friendly, he says. At room temperature, floating in a droplet of water under a microscope, this accursed bacterium looks comfortable and gorgeous. The cells of one strain isolated from a rock in the Negev glisten like a translucent green iris. But when the water dries, their bodies shrivel into much smaller gumdrop shapes. In this stance, the bacteria resist drying for decades.

Hot and cold, high and low--you might expect to find different microscopic pariahs at each extreme, just as you find penguins at the poles, and camels in the deserts. And yet one type, above all others, consistently wins the prize--best survivor in hot deserts, best in cold deserts, best in salty environments. Chroococcidiopsis may well be the toughest photosynthesizing organism on Earth. So why won’t it live in nice places? Why don’t the wretched, being so miserable yet intrinsically tough, rise up from the deserts, come down off their mountains, shake off their shackles of ice, and take over the planet?

For a strange situation, Friedmann has a strange explanation: microbes much like Chroococcidiopsis did, at one time, have the run of the planet. This cyanobacterium, Friedmann says, was quite common about 2 billion years ago; we believe that this is the most primitive of the still- living cyanobacteria. In those earliest times, he argues, at the very beginning--what I call the good old times, when life originated on Earth-- the problem was how to survive under sometimes rough conditions: it was too hot, too this, too that. But one thing was not present: lack of food. So competition was not here. Competition came later, when different types of organisms arose. Some were more specialized to certain conditions than others, and those more specialized ones squeezed out the less specialized ones from a good niche. So there are, even today, some organisms--such as Chroococcidiopsis--that on the one hand show incredible tolerance to all kinds of environmental conditions, and on the other hand seem to lack the ability to compete. They are not aggressive competitors; they are just survivors. They are being pushed to the limits of existence, where nobody else wants to compete with them.

At this point in Friedmann’s conjectures, another planet--Mars, of all places--becomes convenient for completing the tale. Indirect evidence for life on Earth (organic compounds preserved in rocks, produced only by life) goes back at least 3.8 billion years. Yet life could not have appeared on the planet’s surface, most agree, before about 4 billion years ago, when heavy meteorite showers were still vaporizing the oceans. As proof for the existence of full-blown cellular life keeps pushing closer to 4 billion years, evolutionary biologists wonder if there was enough time for such life to arise from basic organic molecules.

Perhaps life only arrived on the surface of Earth after it originated somewhere else. It’s been suggested that it started deep in Earth, where it is still abundant, and later moved up to the surface. Another suggestion, which Friedmann favors, is that it arrived ready-made from another planet. Mars is smaller than Earth and farther from the sun. Therefore Mars cooled down earlier. Probably the conditions suitable for life to arise happened earlier on Mars than on Earth, says Friedmann. And because the gravity of Mars is weaker than Earth’s, it is much easier for something to travel from Mars to Earth than the other way--something like a meteor, chipped off the surface. So if we assume that life originated on Mars and came to Earth, Friedmann continues, then we gain more time to explain the origin of life.

During the solar system’s infancy, when huge meteorites were regularly smashing into the planets, a fair amount of Mars could have made its way to Earth in a matter of months, and some of it could have been infected with Martian microbes. (While an impact vaporizes the rock at ground zero, it also launches outlying material into space without doing too much harm to it.) Assume, for a moment, that microbes are riding one of those rocks, possibly inside it. Little DNA would be damaged in such a short period of time, and so they could simply turn off their metabolic engines in the cold vacuum of space. Bacteria on small meteorites would die as their spaceships burned up in Earth’s atmosphere, while large meteorites would detonate on impact. But a medium-size one would be braked gently by the atmosphere, would not get too hot in its core, and would hit the ground relatively softly. Bacteria riding these impactors might well survive the landing: such meteorites also have a habit of breaking up while still in the air, and the fragments would disperse microbes over a large surface area, like interplanetary seedpods.

The fanciful notion that life spread through space--known as panspermia--has been tossed around for decades. Originally it was proposed as an interstellar inoculation, but now researchers are beginning to think seriously about a local, Mars-to-Earth version. In order to make the journey, a microbe would have to be a rugged generalist. Being tough, it would last for months in space, and once dropped onto a new planet, a generalist could thrive almost anywhere. If specialists survived the ride, by contrast, they would quickly die unless they were lucky enough to land on a spot to their liking. And here is where Friedmann’s scenario comes full circle: here on Earth, he has seen just these qualities in primitive, now-outcompeted microbes like Chroococcidiopsis. Maybe, in the larger sweep of cosmic time and space, similarly wretched survivors will turn out not to be wretched at all but rather the preponderant type of life, skipping ahead from planet to planet, or even back and forth as disaster sometimes clears the decks.

Evidence is short for assigning life on Earth such a dramatic origin, and Friedmann is not acting as the idea’s evangelist. Proving it would take, among other things, the discovery of life on Mars--or at least molecules extracted, say, from microbes frozen in permafrost. There are other variants worth exploring. Exobiologists are experimenting with cave- exploring robots that could reach deep-dwelling microbes on other planets. Some have suggested collecting ice fragments from Europa’s frozen ocean and testing them for organic molecules.

Any of these ideas might actually fly. This coming July, if all goes well, the Pathfinder probe will land on Mars, and within the next decade other spacecraft will follow, carrying new experiments designed to search for life. I remember very well, Friedmann sighs, what happened during the Viking program. A lot of joking and infighting about whose program should be adopted. This time, he says, I am not arguing with my colleagues about it. It really doesn’t matter. My guess is as good as somebody else’s, and maybe all of us are right, maybe all of us are wrong. Everybody is betting on something, and whose bet will be the winner--who knows?

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