"Heaven and Earth are large, yet in the whole of space they are but as a small grain of rice. . . . How unreasonable it would be to suppose that, besides the heaven and Earth which we can see, there are no other heavens and no other Earths."
teng mu, CHINESE PHILOSOPHER OF THE 1200S
"So, oft in theologic wars the disputants, I ween, rail on in utter ignorance of what each other mean; and prate about an Elephant not one of them has seen!"
john godfrey saxe
Against the advice of my colleagues, my racquetball buddies, and other people capable of giving me grief, I went to the Bio-astronomy Conference in San Juan, Puerto Rico in July 2007. In writing this book, I have spent enough time reading astrobiology and bioastronomy papers and books to know that the study of life in space is a serious science. It is a field, after all, funded both by NASA and the National Science Foundation. Yet I could not escape the sense that I was about to find myself listening to stories about alien abductions and probes. I packed my bags and flew to old San Juan, steadying myself for what I might find.
As I walked in the door, I saw them, the bioastronomers, or as they are more often called, astrobiologists. They were identifiable immediately among the larger crowd of hotel guests, in no small part thanks to the conference's giant name tags that dangled around necks as a kind of social shorthand. Don't worry about introductions, just read my name tag to see who I am and whether I'm from somewhere you think is interesting. I picked up my own tag, "Rob Dunn, North Carolina State University," and headed in, fully disguised.
I would come to find that the astrobiologists were not, on average, particularly debonair, socially adept, or good at knowing which fork to use. They were focused on their own work, often to distraction and beyond reason. They discussed, without any sense of a need for introduction, obscure constants or principles. No one was wearing a Star Trek uniform, but neither were there many fancy suits. These were not outsiders to mainstream science, but instead the kind of slightly awkward and very obsessed scientists I was familiar with,* my people.
One imagines that scientific meetings are about science, but most—the bioastronomy meeting included—are more about socializing, about people engaged in similar quests coming together to meet at the pool and drink a few too many margaritas. In the hot tub, excitable students talked about whose science was flawed, who got grants but should not have, who got what new job, and the great things each of them was about to do. An old man with a comb-over flirted with young students long into the night hoping that intellect might succeed where aesthetics had fallen short.
Yet among the daily foibles, the tug of sex and ego, was big science. Peppering the conversations about what Ellen said to John or the inherent loveliness of the woman in the yellow skirt were mumbled statements about new samples from Mars, where life evolved and what its limits were, or the striking diversity of organic material in meteorites. I ate lunch with a young scientist who had just written a paper on the dimensions of the ancient seas of Mars, and dined a different day with the man now in charge of leading the search for intelligent life in space and listened to talk after talk. Here juxtaposed were the banality of daily life and the grandeur of the universe. Noon: two scientists flirt over sushi. One o'clock: discussions of the origin of life.
* Lest I pass up a chance to return the grief, they reminded me of my racquetball buddies.
Among the attendees were, in hard to discern proportions, visionaries, fools, and ordinary scientists adding small pieces to the big picture. The more visionary among those present were close enough to the edge of the unknown, the raw frontiers of science, to make big mistakes. The flops, the wrong theories and misdirected research programs, were career-ending or simply humiliating, but the successes, when they came, could merit announcements on the White House lawn.
That much has changed since the early days of astrobiology was evident immediately at the meetings. For one thing, there are now many hundreds of astrobiologists scattered across fields ranging from marine biology to anthropology. But more important, the field of play has changed. When Frank Drake and Carl Sagan began looking to space, we had a handful of planets to explore for life and few astrobiologists to do the exploring. We have now discovered many new planets, and it is no longer far-fetched to think that stars with planets are common. Planets that are like Earth in terms of composition and climate now seem potentially numerous. Life can exist under far more severe conditions than was once imagined. On the eve of the Bio-astronomy meetings, the possibility of life on other planets seemed, among those attending, as great as ever.
In John Godfrey Saxe's telling of an ancient Indian story, six blind men come upon an elephant and attempt to describe it. One man handles the ear and thinks the elephant a fan. One man brushes the elephant's side and thinks it a wall. One man grabs the elephant's tusk and is sure he has a spear. The man holding the trunk thinks he's discovered a snake. The last man feels the knee and finds it to be very like a tree. Among astrobiologists are, it seems likely, some of the next generation of discoverers, individuals whose views of life will change the way we see the world. It is not, however, obvious who those discoverers are. There is no shortage of ideas in astrobiology that, like the possibility of nanobacteria, are both revolutionary and not yet accepted. Some of these ideas are wrong, but some are right, and it is hard to judge which are which. It is difficult to see the forest for the trees, or, as in the old John Godfrey Saxe story, to see the elephant for its parts.
The blind men before the elephant are thus, in their way, like astrobiologists or like scientists in any new field at the frontiers of knowledge, for whom it is clear that something is being revealed, but not very clear exactly what it is. In Saxe's story, the men never figured out what the elephant was. But in science, sometimes we do. Incorporating disparate observations often depends on the whip of an individual scientist's insight, but also on discussion, the informal milling of ideas. Meetings and other chances for more informal discussions are sometimes where the bridges between separate perspectives begin to come together. In some ways, the exciting science is not in the talks, which are usually small pieces of bigger pictures, but in the conversations. If conversations across bathroom stalls, coffee tables, dinner tables, and hot tubs were any indication, Mars remains the elephant that has not yet come into focus. "Mars" was uttered often enough that one had the idea that it was close at hand, that under the right light and with a strong enough rum one might look out from a hotel balcony and see Martian life with the naked eye. From Mars there was new and better evidence of where ancient oceans had been, new evidence of compounds that might favor life, evidence of methane, and new evidence of caves where underground life might live on. I watched as a man, talking to someone in an animated way about the potential caves, walked into a column in the hotel lobby. Few would accuse astrobiologists of lacking focus.
We have yet to walk on Mars, yet to scoop Martian soil with our hands and sift it, looking for the shimmer, the undeniable signs of life. We will, it seems, one day go and look for ourselves. In the meantime, scientists study, actively, fervently, fanatically, those places on Earth that might be like Mars, the rock and subsurface of our planet, the most extreme conditions here. If there is life on Mars or elsewhere in the universe, it is the kind of thing that would live in places on Earth we don't travel to often, the kind of places professors send their graduate students.
Astrobiologists, including many of those present at the meeting, now look to extreme life as a measure of what might live on Mars and other planets. That is what they seek, but they may eventually discover something else entirely. One possibility that Saxe's story does not mention is that one of the blind men has walked past the elephant and grabbed another creature. In looking to extreme conditions on Earth, astrobiologists believe, in part, they have grabbed hold of part of the story of life in space. Their discoveries might, with time, yield that story, but the other possibility is that what these scientists have found is simply a new view into life on Earth—one independent of whether there is life elsewhere in the universe, but one that will change our place in the world.
Life is now known to inhabit some of the coldest and hottest conditions known on Earth. Hot springs are filled with life. The hottest deserts blossom with microbes. Your gut is bountiful,* we now know, as are clouds up to twenty-five kilometers in the air, and even falling snow. Microbes have been found on radioactive sludge, and in some of the most unforgiving corners of the planet. But conditions for life in space, some astrobiologists argue, might be even more hostile than clouds, snow, or deserts. They might be as inhospitable as the deep sediment and crust of the Earth, where for most of history no life was known.
To understand the living Earth, imagine yourself riding a horse. You are riding along a trail among the green life of the planet: trees, bushes, and the clinging beasts, your horse included, that eat them. Gravity presses you and your horse to the ground, so that neither of you slings out into space. Below your horse's feet is soil, a realm built
* Nothing personal. So is everyone else's.
of tumbled-down rock and bodies, which, after inches or meters, gives way to rock. Farther down are miles of crust, the ancient and fractured stone that we take for granted. The soil and the green life are, at most, tens of meters thick. The deep soil and crust are, together, many times as thick, in some places extending tens of miles. Their depth varies. In Florida for example, you are much closer to the hellish world below (as has long been the suspicion of people from the state of Georgia). Below the crust is mantle, which is almost two thousand miles thick, and then, at the imagined center, the core.
You and your horse, the green trees, and everyday life we are accustomed to, are nearly invisible when the Earth is viewed in cross-section. In cross-section, the Earth is basically lifeless, or so we had long assumed. As usual, the assumption of lifelessness was sufficient, for a while, to keep us from even paying attention. As I would find out at the meetings, and by talking to more and more researchers studying the crust of the Earth, the Earth beneath the soil and beneath the ocean floor is very much alive. Those miles on which we walk are moving beneath our feet as the inhabitants of the deep thrive.
Revelation can come in fits and starts. In 1977, the scientists in the Alvin submersible discovered deep-sea vents. In 1991, the occupants of that same Alvin, the great workhorse of the deep sea, stumbled upon something just as remarkable. As before, no one was sure—at least not immediately—what it was. The situation had changed since those first Alvin missions. Now, large areas of deep sea vents had been mapped, the Alvin was better equipped to collect biological samples, and hundreds of papers had been published on the deep-sea vents. If discovery favors the prepared mind (or the prepared submersible, anyway), the Alvin was now ready, just not ready enough.
A crew of scientists, led by Rachel Haymon, a marine geologist, was working in a place in the East Pacific known simply by its coordinates: latitude, 9 degrees, 50 minutes north; longitude, 104 degrees,
18 minutes west. The sites of interest were 8,500 feet below the ocean surface. The group already knew them, in part. In 1989, a camera and thermal system had been towed to map vents over an eighty-two kilometer stretch of the vents arrayed along a long troughlike volcanic caldera. The scientists had the photos and maps from that earlier trip and so now just needed to look for the mapped vents to study them in more depth. On the first dive, Rachel Haymon, Karen Von Damm, and Cindy Van Dover were in the submersible. It was, perhaps, the first all-girl dive.1 They went to an area that they thought was toward the southern end of the vent field that had been mapped earlier. When they arrived at the seafloor, things looked different. The water was cloudy and dark and black smoke was rising around them. Something was, if not exactly wrong, not exactly right either.
On a dive the next day, John Edmund, one of the scientists who had been on the expedition that first discovered the deep-sea vents, went down in Alvin and saw something different. There was white stuff everywhere and then, "it was really amazing. [He] saw this black smoke coming straight out of the sea floor."2 Something was going on and more diving did not seem to immediately clarify the story. When they dove to the north end of the fields, they couldn't find the vents at all. Some began to wonder whether they were even diving in the right place. One geologist on board the ship, Daniel Fornari, thought they were lost.3
On April 14 it was still unclear what was going on. The crew was excited but also a little confused. Rachel Haymon, Karen Von Damm, and Dudley Foster prepared to dive together in the Alvin, but Alvin had a problem—something electrical. If the Alvin does not get in the water by 10 a.m., the mission is over for the day. By 9:50, the electrical problem wasn't fixed. By 9:52 it still wasn't fixed. 9:56. 9:58. Finally, just before ten, two seconds before ten,* the Alvin launched. The crew was very eager to see more and such waiting was difficult. As they arrived at the
* At least in the retelling of the story.
ocean floor, the whole sub went dark. The electrical problem had, apparently, not been completely fixed. They were a mile and a half down in a small submersible without lights. One might panic or at least suggest a return to the surface. Instead the overwhelming sense was that Dudley better get things working, because there was a lot to see outside.
Dudley Foster flipped on the emergency lights and banged around on the panels. Eventually, he got the lights going again and the Alvin and its team went over a small ridge and into the trough in which the vents had previously been found. As they began to approach the ridge, Rachel Haymon saw a tube worm, on its own, a long way from where it should have been. She had time to think, "Hey, what is that tube worm doing there?"
As the Alvin rounded the hill, the tube worms, crabs, and other life seen in the photos of the site were gone. In their place was a blizzard of white forms, a blizzard, somehow, like the Milky Way. As far into the distance as they could see, the sea was speckled white and the specks were being blasted up in the moving water. The scientists would later struggle with words for the forms: "white flocs," "foam," "white debris," "white-stuff." It was a density of white before their lights that rose to at least thirty meters—ninety feet above the ocean floor. Below them, the seafloor was coated with centimeters of dense accumulation. The scientists had no idea what it was, but it had them surrounded.4
Above the Alvin were thousands of feet of dark, cold water. The Alvin's was the only light for miles in any direction, save the possible glowing appendages of deep-sea fishes (a glow that often comes from the collective action of symbiotic microbes living in the fish). Despite the smallness of the foam-flecks relative to the sea, they seemed important. The poet Rumi wrote that "the eye of the sea is one thing and the foam another. Let the foam go, and gaze with the eye of the sea. Day and night foam-flecks are flung from the sea. . . ." Here for a moment, there might be more significance to the foam, to the blizzard of strange forms, than to all the rest of what was around them to every side, the miles of dark, cold sea.
While in the Alvin's cramped quarters, scientists disagreed as to what the white forms might be. The chemists on board thought the forms must be life. The biologists thought they must be chemical, non-life.5 Each thought that what they were seeing was so new and strange that it must belong to the other. But the question of what the white forms were was not even the most immediate concern. The entire seafloor was white—but that wasn't all.
There was water coming out of the walls of the trough and out of a particularly large fissure. Then there were the shredded animals splayed around them. It was like a crime scene. Whatever had happened, it had been sudden and violent. There were not only dead but also dying animals. "Thousands of tube worms and mussels—dead. They were scorched and shredded and blown up." Stranger still, there were no scavengers on the bodies on the ground, as though whatever happened had just happened, moments prior. It was like a train wreck, but where was the train? And then everyone saw it at once. There was, mixed with the white flocs, an ash, a gray-looking ash and in the ash, glass shards around them. The glass, they would later find, had hydrothermal minerals, pieces of animals, microbial mat (sulfur), and sulfide impregnated in it. It was then that they knew they were staring at the evidence of an underwater volcano, a volcano so recent that the crabs had yet to come to eat the animals that had been killed.
When the Alvin came up, everybody was anxiously waiting to hear what had been seen. Haymon and crew pulled out one of the samples they had taken, a dead tube worm. It smelled like a barbequed hamburger.* There was soon no doubt what had happened on the seafloor.f Nor would that first dive be the end of the excitement to the discovery. The expedition was, for nearly all involved, the most remarkable experience of their lives.
* Hence the name eventually given to the site, "Tubeworm Barbeque."
t Perceptions differ about when consensus was finally reached that what had been seen was the aftermath of an underwater volcano. It may simply be that individuals differed as to when they accepted such a possibility.
With more visits to the rift and vents, the story would become more concrete. They had driven through water murky with mineral particles, which is what had made it hard to see. They were not lost, as had been at some points suspected, but instead the landscape underwater had simply been transformed by the eruption. The tube worm they had first seen had been thrown from its position by the volcano's blast. Many of the other animals were dead, gone, or enveloped in the white stuff (which still needed explanation), underneath which there was just dark, glassy lava. The lava they collected from the site was later dated and the conclusion was that the eruption had occurred between March 26 and April 6. The first dive had been on April 1.
Seafloor volcanoes happen often. Several kilometers of lava erupt from mid-ocean ridges every year. But it is rare to see the aftermath of such a volcano. In fact, it had never been seen before. Yet here it was before them, gloriously revealed.
The discovery of the deep-sea eruption, like the discovery of deep-sea vents, would again find Carl Wirsen. Wirsen had been working on microbes that used hydrogen sulfide as an energy source long before the discovery of the deep-sea vents. During that work, Wirsen, along with Craig Taylor, another Woods Hole biologist, made a discovery that now seemed relevant to the underwater blizzards Haymon and colleagues had seen. In 1977, Taylor and Wirsen found that some of the coastal and marshland bacteria that derive their sustenance from hydrogen sulfide produced a filamentous substance as a by-product of their metabolism. The filaments allow the bacteria to attach to rocks or other organisms. The adaptation was, for lack of a better word, ingenious.
With time, Taylor and Wirsen realized what you might have already guessed as you read along, that the white flocs of the deep sea were also produced by bacteria.6 The blizzard was, in fact, a ninety-
foot-tall cloud of bacteria and bacteria excretions.* This flowering of life and its products had come out of the cracks and caves in the crust of the Earth through which the magma moved as it had escaped. Life had been coughed in a dense cloud out of the realm of the world once thought lifeless.1 The blizzard was not alive, but the organisms that produced it most definitely were.
Although the bacteria that Wirsen and Taylor had found in coastal habitats and those in the vent looked similar, and were alike in producing sulfur filaments, it seemed very unlikely that they were closely related. Superficially, their habitats could not be more different. Yet when the bacteria were later identified (on the basis of their rRNA, thanks to Carl Woese), the species in the coastal environments and on the deep-sea vents were shown to be closely related, both from a genus they would call Arcobacter. It is a long curved sausage with thin waving flagella, waving as it motors through interstices of the Earth, through cavities we had thought barren. As often seems the case, once it was found in coastal water bodies and in the deep sea, it has since been found in many more ordinary places.*
Arcobacter metabolizes hydrogen sulfide and produces the sulfur blizzard as a by-product which is then, in and of itself, useful to the bacteria. When dense enough, the white material forms mats of sulfur. The mats keep the bacteria, and potentially other organisms, from washing away. In the years after the eruption, many multicellular creatures would colonize the new microbial mats. Out of the lifeless crust of the ocean, let there be life.
* Made of nearly pure elemental sulfur.
t In their 1999 paper on the bacteria, Taylor, Wirsen and a third collaborator, Françoise Gaill, were able to show that the bacteria can colonize and reproduce very rapidly. A metal ring placed near an actively flowing hydrothermal vent was soon covered in the bacteria and their sulfurous filament.
* In fact, within the year it was realized that the Arcobacter producing the sulfurous flocs at deep-sea vents and in coastal marsh habitats could be found in sewage sludge, groundwater, and, most exotic of all, broiler chickens.
On its 1991 expedition, the Alvin found a new species of bacteria living in new ways, but what it really did was to provide a visual measure of the possible abundance of life in the crust. If you remember the Earth in cross-section, the broader significance becomes more clear. In the rock beneath the zone that we think of as living, the Alvin crew had just found dense clouds of life. Much of the subsurface and crust, with a combined volume many times larger than the entire surface of the Earth, could be living. The question is no longer whether the subsurface and crust hold life, but to quote the microbiologist Norman Pace, "how deep, how hot, and how much."7
While most biologists realize there is life at the bottom of the sea, that it was so abundant is surprising. We imagine that it is only the surface of the Earth where life is possible. We imagine that the "good" conditions for life are those where we can live. The Alvin, as it drove through clouds of bacteria, clouds of life expulsed from the Earth, showed that this idea is wrong. It showed it in such a way as to alter the lives of those who experienced it. Rachel Haymon, when talking about the moment, was repeatedly at a loss for words to describe the discovery. Yet the Alvin's discovery was not really the first, nor has it been the last, discovery of life in the Earth's subsurface and crust. It was simply among the most obvious indications of what we might be missing. The rest of what lay below would prove even more astounding (at least to me).
The story, or a story anyway, began much earlier, almost ninety years prior. In the 1920s, Edson S. Bastin, a geologist at the University of Chicago, was studying water extracted from deep oil fields in the subsurface of the Earth. The water contained hydrogen sulfide and bicarbonate. On the basis of those observations, Bastin hypothesized that perhaps there were bacteria at the bottom of the wells consuming the organic components of oil. Bacteria might be common in the terrestrial crust of the Earth. His suggestion was too improbable to be credited, but Bastin, along with collaborator Frank E. Greer, also at the
University of Chicago, would go on to culture bacteria from samples taken from deep oil wells. To the extent that there was a response to their work, it was entirely negative. The bacteria were, consensus would soon have it, contaminants. There was nothing that deep. By now, you should be familiar with this plot.
Bastin and Greer ignored their critics and made the even bolder prediction that the bacteria they found might be hundreds of millions of years old, trapped by the layers of rock, a kind of living history, an Eden of the once and former world.8 Bastin and Greer's speculation about the ancient creatures beneath the soil were, for decades, ignored. The dogma remained that deep life did not exist and if it existed, it was recent—a contaminant introduced by the scientists themselves.
Bastin and Greer's theories would not be fully rescued from oblivion until more than forty years later. The first prominent rescue drew nearly as much criticism as Bastin and Greer's original work. In 1992, Dr. Thomas Gold, a scientist of broad interests at Cornell University, theorized that microbial life was widespread in the terrestrial and marine subsurfaces. He went on to speculate that if the biomass of these habitats were spread on the land surfaces of the Earth, it would be a microbial sludge five feet deep.9 Gold did not yet have enough data to make such a statement. He was guessing, wildly, but that did not mean he was wrong.
What was needed were very careful drilling operations that systematically extracted samples from the subsurface sediment and rocks, both on land and at sea. A series of well-documented but poorly known studies would be done in the United States that very clearly demonstrated the existence of very deep life in the terrestrial subsurface.* They were, for the most part, ignored. Finally, in 1994, University of Bristol geomicrobiologist John Parkes and his colleagues dug a deep and relatively high-profile hole. The hole, drilled in the floor of the
* When the U.S. Geological Survey and the Environmental Protection Agency began to study, among other things, how to clean up nuclear sites, they took deep samples to see how far the contamination had reached. In those samples, they too found life.
Pacific Ocean, extended to a depth of seventeen hundred feet. In that hole, samples were carefully (very, very, carefully) extracted to later be analyzed for life. Parkes had an idea of what he might find. He had suspected some of the possibilities for a while, but before he made anything public, he needed this big sample. The big sample came back, and it was full of life. Life was not only present in the drill hole, it was diverse, and it extended as deep as the hole had gone. There was, in fact, little sign that the sample had come anywhere close to the deep limit of life. As the authors would state in their research article, "it is likely that bacterial populations are present to much greater depths."10 Subsequent research by Parkes and others only makes this point more strongly. In some cores that have now been taken, the abundance of bacteria actually increases rather than decreases as one goes deeper into the Earth.
Many studies have now taken deep samples not only of the subsurface of the ocean, the ocean's sedimentary depths, but also the terrestrial subsurface. They have nearly all found life. Bastin has been unequivocally vindicated. The deep Earth is no longer barren. It, too, is occupied. As cores have gone deeper and deeper, Bastin and Greer have been vindicated to a greater and greater extent. Once, we thought that most of the sea was dead. When we found life near the bottom, we still imagined that the seafloor was dead. When we found life on the seafloor, we still imagined that the subsurface was dead. When we found life in the subsurface, we imagined—again, with no evidence— that the deeper subsurface was dead.
As more and more studies are conducted in the deep layers of the Earth, scientists are beginning to see patterns. They are fuzzy patterns, but they might offer a glimpse into what is going on. In subsurface areas where nutrients are rich, microbial life is rich and does not yet seem to decline in abundance or richness with depth. Where nutrients are less abundant, life seems to decline in abundance with depth (one suspects the same trends could hold for deep sedimentary layers in the terrestrial realm, but it remains unknown). Where deep-sea vents are found, near the rifts in the bottom of the oceans, the story is different still. Microbial communities are dense and diverse around the vents.
All of this activity rests on the bedrock beneath the seafloor sediment and terrestrial soils. A next obvious question is what lives in that bedrock. The answer, again, used to be "nothing." It now seems that the answer may actually be "something," or even "quite a lot." No one is sure yet, except the advocates of the new theory (the advocates always being self-sure). What has been found is a kind of fossil world in basalts, fossils quite possibly of microbes. Biologists have theorized that the fossils represent the use of the chemicals in young basalt by microbes. The idea would be that young basalts, those that form during volcanic eruptions, are colonized by bacteria. The bacteria then produce acids that wear at the basalt and cause the release of useful chemicals. As the basalt ages, the microbes remove all of the useful chemicals and die off, leaving the fossil holes. If right, this theory would push life much, much deeper into the Earth. If right, this theory would, yet again, increase the extent to which the Earth is microbial—the rock, the dirt, and everything else could be riddled with life.
It is tempting to try to estimate how much of Earth's life is microbial. It could be that most of life on Earth is in the subsurface, that we, and by we I mean all of the life aboveground, are the minority. It is hard to say, in part because it is not easy to estimate the density of life in the subsurface. When Bastin and colleagues first found microbes in deep samples, they looked at them through microscopes. But they could only see microbes that were culturable (meaning that they could be grown in the lab), which most microbes from extreme environments don't seem to be, and therefore they missed most of them. When other methods were used, which counted actual cells, more individual organisms were detected, but one could not tell who was who. When DNA techniques were used (samples were simply checked for which genes they had, without ever seeing the microbes themselves), very dif ferent species were found and many of those from the cell cultures were missed. Over time, these three methods—looking at culturable cells, counting all cells, and looking at DNA—are helping to produce a picture of life in the crust. It is still a sketch, but in the way that Picasso's drawings are "just sketches." As a simple curve might suggest a face, the samples of the crust suggest a world.
In that world, microbes are far more common and diverse than anyone had anticipated. Multiplying the density of cells in these samples by the volume of apparently habitable subsurface on Earth (excluding the rocky miles beneath the subsurface) yields the amazing estimate that as much as half of the weight of life on Earth is in the subsurface.11 Let me say this again, for clarity: it has been estimated that as much as half of all the weight of life on Earth could be in the subsurface. When I was born, most reasonable scientists thought the subsurface was dead.*
We have only begun to understand that the ocean's subsurface is full of dividing cells. How much life all this amounts to seems impossible to say for now. Every time someone makes an estimate, someone else makes a new discovery. Just this year, Tullis Onstott and colleagues at Princeton University raised the bar again. I'm out of superlatives, so let me just describe the results. Onstott sampled the groundwater in rocks 2.8 miles down near a South African gold mine. The water, On-stott and crew estimate, has been separate from surface water for several to tens of millions of years. In that water, they found microbes, just like in nearly every other sample that has been taken in recent years. What was surprising was that these microbes were not using oxygen from photosynthesis. Nor were they using nutrients from sediment. Instead, these microbes, both archaea and bacteria, were using, exclusively, the energy produced by the radioactive decay of rocks.
* Of course this estimate is, as Dan Janzen said of Terry Erwin's estimate of tropical arthropod diversity, bullshit. It is rough and, like Erwin's estimate, could be wrong in either direction. It may be that much less than fifty percent of life is in the subsurface, but it could also be that it is much more.
Like many of the places microbes have now been found, the mines in which Onstott and collaborators sampled do not seem to us terribly pleasant. It is, "a lightless pool of hot, pressurized salt water that stinks of sulfur and noxious gases."12 Yet the more we sample, the more such conditions seem like the average living conditions on Earth. The most common microbe Onstott found in his samples, a new lineage most closely related to some of those species found near deep-sea vents, seems to find the conditions enviable. It has persisted for millions of years and during that time has undergone many times more generations (and hence more evolution) than has occurred during the entire history of vertebrates. One does not need a degree in microbiology to realize that if the rocks that Onstott sampled had microbes living independent of the sun, so too might many others, perhaps even most others.
Onstott has also suggested, at this point quite speculatively, that the microbes he has found might be the closest thing to what early life was like. They might have been, he extends further, living like this for the entire history of life. They might be our ancestors, the ancestors of all life. Earthlings might have evolved in the crust. It might be home. All the rest—the trees and birds, the bears and bear lice, the men and women—might be something secondary, something we moved to. If this theory is right, the places we love on Earth might be, from the perspective of most life, very exposed, very cold, and very low in pressure—hardly a nice place for them to live. To us the sulfur of the deep-sea vents or Onstott's ancient rocks is toxic, but to the microbes in the ancient rock, oxygen is far more so. To those microbes, we live in the least hospitable place in the planet. If they ever evolved consciousness, cities, and science they would begin by predicting that no life exists on the surface of the Earth, not where temperatures are so extreme, pressures are so low, and everything basks in the sun's deadly light.
As for Onstott, by looking to the ancient rocks for signs of life elsewhere, he is hoping, like Frank Drake, Carl Sagan, and many others that the microbes on Earth can ultimately show us something about life more generally in the universe. When asked about what he found most exciting about his new discovery, he did not hesitate to say, "What really gets my juices flowing is the possibility of life below the surface of Mars. These bacteria have been cut off from the surface of the Earth for many millions of years, but have thrived in conditions most organisms would consider to be inhospitable to life. Could these bacterial communities sustain themselves no matter what happened on the surface? If so, it raises the possibility that organisms could survive even on planets whose surfaces have long since become lifeless."13 While On-stott waits for life in space, he busies himself with what he has found here—an entirely new world, underground.
Back at the bioastronomy conference, the sun had just risen over the bay where Sir Francis Drake once tried to take San Juan. On the streets, families went about their days, businessmen tried to put themselves together after late nights out, and the clouds overhead cast long shadows between buildings and into the nearby sea. I left my hotel to get on a bus. After two days at the conference, two days of hearing about the possibility of life, I wanted to see the real stuff. It is nice to talk about space, but outside the hotel were the more tangible realities of my surroundings—tropical forest, long beaches teeming with critters, and the living sea. I took one of the conference tours because it seemed potentially interesting, but also just to get out. Enough watery conference coffee and discussion of the potential for distant life. I wanted to see some bugs and trees.
The tour was to take us to the Arecibo radio telescope, where Frank Drake and Carl Sagan listened to space together. Drake ultimately listened for years. Sagan listened for a few days and was bored. From Drake's perspective, Sagan found the waiting unbearable. Drake continues to wait and watch. We would see one of his stations where, among the calls of local birds and insects, he thought he heard more distant beacons.
I had been up late the night before, and so even after a strong coffee (finally), I stumbled up the steep bus steps. As I got on the bus, the tour guide looked familiar. I had seen him somewhere recently. I could not quite place him. He was an older man with a friendly sort of countenance, but serious, lively eyes. He was familiar in a grandfatherly sort of way, but there was something else. I wondered if he had been one of the speakers.
Eventually, the bus door shut and the familiar-looking man began to talk. He said, "I'll be your tour guide today. I think everyone here knows who I am, Frank Drake. Now let's begin the tour." In trying to take a break from the bioastronomy conference, I had stumbled onto a tour led by Frank Drake, father of the search for life in space, perhaps the most patient man on Earth. It was his simple math that had predicted there might be dozens of civilizations in space trying to communicate with us. Now he would spend the next two hours on the way to the telescope (for many years his telescope, when he was its director), waxing on about the history of Puerto Rico, astronomy, cultural differences between mainlanders and islanders, and anything else anyone asked about. He began with the story of the history of Puerto Rico. Surely, by now, Frank Drake would have hoped to have been explaining to tour groups what we know of intelligent life in space. But since we know nothing, here he was offering the story of Puerto Rico, which was still somewhat foreign to most in the group.
Soon Drake was telling the stories of the two times he really thought that in searching the sky for signs he had had a response. The first of these occurred when he was twenty-six and he witnessed the false-positive at the Agassiz Station, when his hair turned white almost immediately. He also told stories of his namesake, the pirate Sir Francis Drake. Sir Francis Drake had invaded San Juan through the small canal adjacent to our hotel. The Spanish put a cannonball through his cabin, and he forced the ship to turn back around, having barely survived. He came back to invade again, this time closer to Arecibo. Upon hearing of the invasion, a local official told his army to ride their horses out into the surf and hold their swords high to scare off Drake and his men. All seven men did as they were told. The ruse worked and the land that would hold Arecibo was saved from the first Drake. Sir Francis Drake turned back prematurely and was denied whatever local riches were available, something Frank Drake could never be accused of. He has never, in looking to space, turned away.
When we arrived at the telescope, we were taken on a walk around it. It is the size of a football field. Around it, the jungle tries to reclaim the land. Above it, the sky offers up its radio signals that, like the calls of animals in the forest, are obvious to some, but lost on most. The telescope does not move, but simply scans the skies as the Earth wobbles and spins. The contraption of metal and wires seems both beautiful and primitive. It is, after all, a giant metal ear.
Frank Drake stood beside the telescope with us, talking about his quest, about the mechanics of the telescope and about its fate. He has done much in his life, but when one is the namesake of an equation that relates to our place in the universe, it is hard not to focus on that single achievement. Even among our group of scientists, who knew of his other feats, the equation and his quest were the focus. One of the young astrophysicists posed with Frank for a picture. He then, before snapping another and instead of saying cheese, asked Drake, "what is N?" which is to say, how many other planets with communicating intelligent life-forms are there? Drake yelled out "one hundred" and held up his big index finger. But the fates intervened, as the camera's batteries turned out to be dead. The moment was silly, and yet the quest remains filled with grandeur and possibility. I am not convinced that intelligent life is calling to us, but if it is, how could we not listen? Beside Drake I felt, for the first time, that we must try. For a moment, I forgot to look at the ants and trees.
I cannot help but notice some coincidences. Terry Erwin, when pressed about his gut sense as to the number of species on Earth, said a hundred million, roughly a hundredfold what is known. Now Drake, when pressed on his equation about intelligent life in the universe, guessed similarly—a hundredfold higher than the one sort of intelligent life-form we know. Regardless of the specifics (and how serious either was about their estimates), what both were saying is that most, perhaps nearly all, of the living world remains unknown.
Of course the unknown Drake is guessing about is the bigger of the quantities, because even if just one new planet with life is found, whether that life is as intelligent as humans or as dumb as rocks and microbes, we begin anew with our questions about life and its dimensions. If there were one more planet, might there not be two? And if two, why not four or five or, indeed, hundreds? No wonder Frank Drake has never turned back.
In the end, as science looks forward, there are choices among temptations. It is tempting to look only out to space, to imagine that we have discovered most things here and to get ready to move on. It is an undeniable draw. Few discoveries could be bigger than discovering an entirely new planet and, potentially, a new origin of life. I am not sure there is anything that could be more important, more lasting in its influence, or more confusing to our sense of the status quo than discovering we are not alone, but that is not where I will put my money for the next big discovery. I will look instead to the small life here on Earth. I will look instead toward the center of the Earth—or if not quite the center, then somewhere thereabouts. I have a good chance of being wrong, but so does everyone else. I can already tell you part of what the next big discovery will mean. Whatever it is, it will make us less unique. It will make us, with our grotesque size and overwhelming confidence in our intellects, seem even more like a peripheral body in the orbits of life.
If Copernicus left us feeling like we were the inhabitants of one ordinary planet among many, the similar revolution in biology leaves us feeling even less than ordinary. We are not an average life-form among many. We are a relatively rare species, living in a marginal habitat at the surface of a planet run mostly by unicellular organisms. We are adapted for a brief window of conditions on a planet that has seen big swings. We are special only in our ability to consider our lack of spe-cialness. The black bear does not realize it is one among millions of similar species. It just goes on eating, mating, and dying. We are here momentarily—long enough to hope, dream, and strive—before we, like the bear, complete the cycle of life. We return not to the earth, as the Bible might instruct, but to insects and microbes. We return to those lives that are so numerous and successful, those lives that are everywhere barely noticed—our breathing, invisible, stars.
There is an added irony to how anomalous we are relative to other life. For all of our self-awareness, we are among those species least able to see the world. Not only are our senses dulled, but we are just less robust, evolutionarily wimpy. Even inside spaceships or in submarines, we cannot go to all of those places where small life exists. When the scientists in the Alvin submarine first saw black smoker vents, their metal thermometer melted in the heat. The submarine protected them, but only so long as they did not get too close to the vent. But the microbes, the deep-sea life, lived right next to the vent, where even our metal surrogates dissolve.
We imagine we will colonize other planets, but we have barely probed this one. We have yet to find a lifeless place on Earth, and there are many places we have yet to check. The surface of Earth is covered in unstudied life. There are new species, unnamed species, living even in your own body. There is much here still. More than we now know, and more than we can yet imagine.
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