Weird Life: The Search for Life That Is Very, Very Different from Our Own Read online

  A word on nomenclature. New fields of study try on many names, and this one is no exception. The subject of this book might, with varying degrees of justification, be called beta life, hypothetical life, nonstandard life, nonterran life, unfamiliar life, life as we do not know it, alternative biology, and (you knew this was coming) Life 2.0. I’ve settled on weird life because at the time this book goes to press it seems to enjoy the most widespread usage, and because it conveys with great economy the sense of strangeness the subject deserves.

  As we’ll see, in the violent early history of the Solar System, Earth and Mars traded material, some of which may have been biological. A few scientists argue that life we know may have emerged from spores of extraterrestrial origin. For the time being I will sidestep the question of place of origin, and unless otherwise noted, I’ll use the term “familiar life” to mean all life—terrestrial and otherwise—that is descended from the single ancestor of all life we know, allowing for the possibility that that ancestor may have been extraterrestrial. Alternately, I will use “weird life” to mean any organism or organisms—again terrestrial and otherwise—that are not descended from that ancestor.

  * * *

  * In the popular imagination, dinosaurs were real enough that Dickens, in Bleak House, could use a resident of the Middle Jurassic to add a touch of atmosphere to a rainy day on the outskirts of London. “As much mud in the streets, as if the waters had but newly retired from the face of the earth,” he wrote, “and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.” (p. 1)

  CHAPTER ONE

  Extremophiles

  Julie Huber is a marine oceanographer working at the Marine Biological Laboratory in Woods Hole, Massachusetts. She is thirty-four but has an easy laugh that makes her seem even younger, and if you saw her jogging on a beach you might take her for a professional volleyball player. Her accomplishments in the field of oceanography and marine biology are many; she has logged nearly a year on oceangoing research vessels, and made several descents in the most famous of all research submarines, Alvin. Her main research focuses on the microbes that live in and beneath the crust of the seafloor. They are organisms that sequester carbon, cycle chemicals, and affect the circulation of ocean water—all of which are activities crucial to the oceans’ overall health. Yet these same organisms happen to be, in the language favored by field biologists, “vastly under-sampled.” Consequently, they have been little studied and so are little understood. They are also in places so difficult to reach that if Huber hopes to study them she must use techniques from various disciplines, among them geology, genetics, and molecular chemistry.

  Dr. Huber is possessed of a passionate intellect that can catch you by surprise. She will look you straight in the eye and affirm that a certain development in microbiology “really excites the marine sediment community.”1 While you register the fact that there is a marine sediment community and consider that its members could perhaps benefit from some excitement, she is already explaining, in language that is an unself-conscious mash-up of technical and colloquial, the particular challenges of trying to detect organisms by measuring the chemical components of seawater, noting by the way that certain recent work on methanogen diversity is very cool.2

  Lately Huber has been, in her words, “chasing seafloor eruptions.” She is particularly interested in organisms that live in the Pacific, near three “seamounts” (oceanographers’ term for submarine mountains). All three seamounts are geologically active, and Huber makes periodic visits to each—or, more often, to the place on the ocean’s surface several kilometers above them. The visits usually hold surprises. In May 2009 she was on a research vessel in the western Pacific, only twelve hours out of port in Samoa, when the remote operating vehicle Jason, from 2 kilometers beneath them, began transmitting live, full-color video images of the West Mata volcano erupting. It was 3:00 a.m. on the ship, but everyone—scientists and off-duty crew alike—was crowded into one room watching the televised images of lava flowing, sometimes explosively, from the deepest erupting volcano anyone had ever seen. It was, Huber said, “definitely the coolest thing I’ve seen on the seafloor,” adding wryly, “and I’ve seen a lot of seafloor.”3

  The water in the samples that Jason retrieved from the vicinity of the volcano was as acidic as battery acid, yet it contained living bacteria. There were fewer kinds than at similar sites, and so there was a less diverse microbial community—this the phrase used to describe many populations of microbes living together, sharing resources, and in various ways making life better for one another. Whether the relative paucity of kinds means the environment is too harsh for certain organisms, or whether West Mata’s young age means that things are just getting started there, is an interesting and open question—one that Huber hopes to answer in the months ahead.

  At the moment, Huber is managing several projects simultaneously. Late on a Friday morning in March 2010, she has just received an e-mail from the postdoctoral student studying under her and doing fieldwork on a research vessel near Guam. It seems that they had set markers and moorings on the seafloor and now couldn’t find them. Huber gives a “this sort of thing happens all the time” shrug and suspects the culprit is what geologists, rather unromantically, term a “slumping event.” In all likelihood a part of the seafloor slid sideways, taking the markers and moorings with it. Just another reminder, not that Huber needed reminding, that the seafloor is not the grave-quiet place that only half a century ago, many scientists believed it to be.

  Huber’s research may trace its origins, quite directly, to the discovery in 1977 of the so-called hydrothermal vent communities, and less directly to questions that arose in the first decades of the twentieth century—as to why the continents are shaped as they are.

  A SCIENTIFIC MYSTERY

  Anyone who sees a world map centered on the Atlantic Ocean cannot help but notice that the east coast of South America seems made to fit, jigsaw puzzle–like, into the inward-bending coast of Africa. In 1922 a German geologist and meteorologist named Alfred Wegner went several steps further. Assembling the evidence of fossils, mineral deposits, and scars left by glaciers, he proposed that the comparison was apt. The continents were pieces of a puzzle, pieces that happened to be slowly drifting apart. In the decades that followed, others developed Wegner’s hypothesis into a theory of plate tectonics, which proposed that the Earth’s crust is composed of plates—perhaps ten “major” ones and as many as thirty “minor” ones. It was thought that their upper parts were brittle, their lower parts warmer and more malleable, and that some might be as much as 80 kilometers thick. Geologists found evidence that molten rock was pushing into the seams where the plates had pulled apart.

  If this were the case, it might help to answer a question that was surprisingly long-standing and surprisingly straightforward: Why is the chemistry of seawater what it is? Lakes like the Dead Sea—lakes with no outlet other than evaporation—are called “closed basins.” They are alkaline in the extreme, and they grow more alkaline over time. Logically, since the world’s oceans have no outlet, like very large closed-basin lakes, they should be very, very alkaline. Yet their pH, the measure of the acidity or alkalinity of a solution, was between 7.5 and 8—very near the middle of the scale—and this was the case for foaming breakers in the Florida Keys; for dark, dense water in the Mariana Trench; and for the frigid water lapping Antarctic icebergs. It seemed clear that some process was at work, filtering the water and maintaining the pH, and doing it everywhere. A few scientists began to suspect undersea hot springs, and they had ideas as to their whereabouts. Hot springs on the Earth’s surface were heated by the molten rock in nearby volcanoes; it seemed reasonable to expect that hot springs on the seafloor would also be near molten rock. And many thought there was molten rock in the seams between tectonic plates. Find the seams, many suspected, and you’d find the hot springs.

  But no one knew for sure. Even by the early
1970s, textbooks in oceanography introduced their subject with the startling fact that we knew less about the ocean floor than we knew about the near side of the Moon. If anything, this appraisal was generous. Sonar for mapping the floor was crude, and equipment used to measure temperatures and pressures was towed on cables behind ships. Sooner or later a cable would snag on an undersea rise, and the ship would idle its engines while a dispirited crew pulled the equipment aboard. It usually came back wrecked—unless the cable just broke, in which case it didn’t come back at all.

  The United States Navy, however, had developed sophisticated techniques for mapping the ocean, and by the mid-1970s the navy had begun to share them with researchers. Using these techniques, scientists at Woods Hole Oceanographic Institution (WHOI) implemented a three-stage method to explore a swath of seafloor. First, the research ship Knorr would drop transponders. Because the seafloor is uneven, they would settle at different depths. Then their positions were measured with great precision by sonar, allowing researchers to derive a low-resolution map of the terrain. Finally, a camera vehicle—a 1.5-ton “gorilla cage” mounted with cameras, strobe lights, and power supplies—would be towed over the terrain at a cautious 4 kilometers an hour, 20 meters above the seafloor. Every few hours the crew would haul the vehicle aboard, pull the film, and develop it.

  In the spring of 1977, Woods Hole researchers on the Knorr were mapping the seafloor in the eastern Pacific about 280 kilometers northeast of the Galápagos Islands. After one run over terrain 2 kilometers deep, the film showed white clams. It was obvious they were alive.

  At such moments the research submarine Alvin (owned by the United States Navy and operated by WHOI) would be called into play. By the 1970s she was already something of a workhorse. In 1968 she had been lost once and recovered. Two years earlier, when an air force B-52 bomber collided with a tanker over the Mediterranean Sea and (accidentally) dropped an undetonated hydrogen bomb, Alvin was given its moment in Cold War history and summoned to search the ocean floor off Spain. On March 17, 1966, Alvin’s pilots found the bomb resting on the seafloor nearly 910 meters deep. It was raised intact. By 1977 Alvin had had several upgrades, but its fastest speed was a modest 4 kilometers an hour, and its lights penetrated only 15 meters. Not that any of this mattered. What Alvin was especially good for, and what she is still good for, is close observation. And so, when the Knorr found live clams 2 kilometers beneath the surface, Alvin was towed to the site.

  Alvin’s crew compartment, a hollow titanium sphere 3 meters across, holds three—a pilot and two researchers. The researchers for this particular investigation were geologists—John Corliss of Oregon State University and John Edmond of MIT. They spent most of the 2,000-meter descent peering out the Plexiglas portholes. There wasn’t much to see, and even when they were a few meters above a sloping seafloor, Alvin’s lights illuminated nothing but the hardened molten rock that geologists call pillow basalt. It covered the sloping floor in all directions, making for a scene that, even to a geologist, was not particularly remarkable. Then they noticed something about the water itself. It was shimmering like the air over a hot grill. Hurriedly, Corliss and Edmond took measurements and found that the water was warmer than water at this depth should be, by about 4 degrees.

  The pilot took Alvin up the slope, and when they neared the crest of a ridge they were astonished to see, lit by the searchlight and through the shimmering water, reefs of mussels, giant clams, crabs, anemones, and fish. It was a fantastic undersea garden, an oasis vibrant with life. Corliss and Edmond did not know how the riotous island ecosystem around them was possible. They did know, however, that Alvin had only five hours of power remaining, and they spent that time, Edmond would later write, “in something close to a frenzy,” measuring water temperature, conductivity, pH, and oxygen content, and taking samples of everything that Alvin’s mechanical arm could grab.4 That evening, back aboard the Knorr, there was a small celebration. Someone had a camera and snapped photos of Corliss and Edmond—young men, bleary-eyed and smiling.

  In 1830, British naturalist Edward Forbes claimed that because sunlight could not penetrate deeper than 600 meters, phytoplankton could not survive below that depth. Without phytoplankton, there was no base for a food chain. It followed, reasonably enough, that the deep ocean must be sterile.5 By the mid-twentieth century, the processes by which oceanic life sustains itself were well understood. Sunlight supplies the energy. Nutrients in the form of nitrogen and phosphorus are brought in by rivers and streams and stirred up from the seafloor by upwelling currents. The floating single-celled plants called phytoplankton use the sunlight, nutrients, and carbon dioxide dissolved in the water. They are eaten by the tiny invertebrates called zooplankton that float freely throughout the seas and other bodies of water, and the zooplankton are eaten by shrimp and other crustaceans, all the way up the food chain to the braised tuna with lemon on your dinner plate. Obviously, such processes could operate only near the ocean surface.

  In the decades that followed, however, scientists came to realize that there was life at great depths. Fish, crabs and other organisms lived in total darkness at enormous pressures, and survived by feeding on dead and decaying matter that sank slowly from the waters above. By the mid-twentieth century, advances in nautical engineering allowed biologists to see this life firsthand. In the mid-1940s the Swiss scientist Auguste Piccard designed a vessel he called a “bathyscaphe.” Unlike its predecessor the bathysphere, a simple spherical pressure chamber lowered and raised by a cable, Piccard’s new design featured a float chamber for buoyancy and a separate pressure sphere for the crew. The third bathyscaphe Piccard built was called the Trieste. It was sold to the United States Navy in 1957, and three years later it took Jacques Piccard (Auguste’s son) and navy Lieutenant Don Walsh to the bottom of an undersea canyon called the Mariana Trench. It was there that they noticed, more than 11 kilometers beneath the surface, the deepest place in any ocean on Earth, a flatfish.6

  Still, even in 1977, most marine biologists expected such organisms would be few and solitary. And since recycling of decaying matter in the ocean’s upper levels is fairly efficient and allows very little to sink much lower before it is consumed, they expected those organisms to be quite hungry. So in 1977, when the Woods Hole expedition’s chief scientist called a marine biologist named Holger Jannasch to give him the news of a thriving community of life 2 kilometers deep, Jannasch simply didn’t believe him. “He was,” Jannasch explained, “a geologist, after all.”7

  The expedition would conduct fourteen more descents to the site. It became apparent that Corliss and Edmond had happened upon a hot-spring field. Warm water was flowing up through every crack and fissure in a roughly circular patch of seafloor about 100 meters across. While Alvin investigated the newfound life below, scientists aboard the Knorr studied the water samples already returned, and found that all had a high concentration of hydrogen sulfide. That turned out to be a thread that wove together an entire ecology.

  On land, some bacteria were known to derive energy from hydrogen sulfide through a process called chemosynthesis. They were rare, and most organisms took their energy, directly or indirectly, through photosynthesis. But in the dark 2 kilometers deep, chemosynthesis might be the only synthesis possible. Soon, researchers at Woods Hole developed a model to describe the process. It was this: Deep within the Earth, naturally radioactive materials produce heat that melts rock into the substance called magma. Magma is pushed up through the seams between the midocean ridges, where it cools and spreads outward to become new oceanic crust. Meanwhile, seawater continually percolates down through the crust, where the sulfate it carries combines with iron in the crust to produce hydrogen sulfide and iron oxides. When the same seawater, now heated, is pushed back up through cracks and fissures in the crust and returned to the deep ocean, it carries hydrogen sulfide that certain bacteria find quite tasty. The same bacteria absorb oxygen dissolved in the water, and some of that oxygen combines with sulfite to become sulfate.8


  We would seem to have come full circle, returning to the chemistry we began with. But the story is not quite over. As you may recall from chemistry class, some reactions absorb energy, while others release it. The chemical reaction that yields sulfate releases energy—which the bacteria, in lieu of sunlight and in a model of efficiency—use to drive their metabolism. From here on up, the food chain of what would come to be called hydrothermal vent communities was thought to be, roughly speaking, like that in the sunlit waters 2 kilometers above.

  Corliss and Edmond understood that the water issuing from the vents was probably much diluted as it rose tens of meters through the crust, and that the real action, geochemically speaking, must be in the crust, a kilometer or two deeper down. But they would never see or study that chemistry as it was happening. Or so they thought.

  Two years later, researchers who were using Alvin to investigate warm upwelling on the Pacific Ocean floor near the Gulf of California happened upon its source: natural chimneys of sulfide minerals, 2–3 meters high, furiously pumping water black with iron sulfide and very, very hot. Soon Corliss and Edmond arrived on-site, took their turn in Alvin, and measured the temperature of the water released by the chimneys. It was a nearly incredible 300°C. Under an atmospheric pressure at sea level, if you try to heat water gradually, it will boil away long before it reaches that temperature; and if you heat it rapidly to that temperature, it will boil explosively like (in fact, exactly like) a geyser. It is the pressure of 2 kilometers of water that keeps the chimney’s water well behaved.