Earth in Human Hands Read online

  The landers functioned nearly flawlessly, and provided the foundation for much of our modern understanding of the environment and history of that neighboring orb. But the centerpiece of the mission was the biological experiments, and these taught us more about ourselves and our wet-behind-the-ears approach to life than about any critters in the Martian soil. NASA took the opposite approach from that recommended by Lovelock, searching for very specific signs of organisms in the soil around the landing sites. For reasons that seem a bit questionable with the clarity of hindsight, the Viking experiments were designed to look for life that would thrive under not current Martian conditions, but warmer, wetter conditions more like those found on Earth today. This decision was largely justified by a wishful idea about life on Mars that Carl Sagan had proposed and promoted in the early 1970s. According to his “Long Winter Model of Martian Biology,”2 the Martian climate might flip-flop between its current frozen, dry state and occasional wet, warm spells. Martian organisms might have evolved a “cryptobiotic,” or dormant, phase that would allow them to survive the long cold snaps. Such sleeping beauties might spring to life when the Vikings landed and fed them “chicken soup,” as the mix of water and generic organic nutrients carried on board the spacecraft was called. No such luck. The Viking biology experiments squirted this Purina Martian chow into the dry soil and waited to see if any thirsty creatures would try some and belch, betraying their presence.* If there were Earth organisms living there, we would have found them, but apparently nobody was home.

  At first, one experiment did seem briefly to signal a biological response, generating momentary excitement. Yet, over the hours and days, the results followed a pattern much more indicative of reactive soil chemistry than native life. It wasn’t strange Martian bugs but strange chemistry, something in the dirt that was not like Earth dirt, and was extremely reactive with water.† Today the Viking experimental approach may seem naïve, an attempt to find life as defined by simple geocentric assumptions. Yet perhaps, in our ignorance of how alien aliens might be, it was worth a try to grab some alien dirt and give it a squirt of water just to see. None of our landers and rovers since has included any instruments actually meant to test directly for living organisms. We realized that, short of seeing something in a camera or microscope that is unmistakably alive, we don’t yet know how to design such an experiment. Our search has largely shifted toward finding signs that Mars was once habitable billions of years ago, when it and Earth were young worlds.

  Yet we’d still love nothing more than finding possible environmental disturbances of the kind that Lovelock suggested decades ago, such as strange gases that “shouldn’t” be there. One recent discovery falls into this category: the Curiosity rover has sniffed a possible trace of a strange gas, methane (CH4) that should not be there according to our best understanding of Martian geochemistry, and might conceivably come from living organisms. Right now it’s not clear if the methane is really there, or present in enough quantity to be a possible indicator of life. By the time this book is published, that may become clear.* Either way, the debate underscores Lovelock’s prescience about what a sign of life could look like.

  This line of thought about Mars also led Lovelock to look anew at how life has changed Earth. What if Earth had never detoured down the path of life? What would its atmosphere be like? The answer is that without life, our planet would be drastically different from its current state, in ways that would be obvious to the casual alien observer. All this oxygen, along with healthy traces of methane and several other gases, forms a bright signpost of disequilibrium. That is, it’s an unstable mixture, a chemical house of cards that is actively propped up by the ongoing activity of abundant life. To any extraterrestrial astronomers examining the inner planets of our solar system, this condition would shout, “Hey, look at this one!” If it is life they were seeking, the aliens wouldn’t give airless Mercury a second glance, and they’d likely, after a quick spectral examination, pass on Mars and Venus, finding their stale CO 2-dominated atmospheres unpromising. But Earth would stand out as strange and perturbed, with something in the air that geology and chemistry alone could not explain, with some huge ongoing, active chemical disturbance. That disturbance is life, and were it to disappear, or had it never evolved on Earth, the molecular oxygen (O2) would largely vanish from the air. A promiscuous element if ever there was one, oxygen never stays single for long. Without life’s continuing input, oxygen would have long ago hooked up with whatever elements it could find, and the carbon would have reverted to its more stable form, carbon dioxide. In other words, the air of a lifeless Earth would closely resemble the nearly pure CO2 we see on Mars or Venus today.

  His efforts and insights in the area of life detection led Lovelock to a new view of the role of life on Earth. The full realization of this vision came about when the maverick chemist teamed up with the brilliant renegade biologist Lynn Margulis.

  Mother of Gaia

  The last time I saw a roomful of scientists cry was at an Indian restaurant a few miles south of the Kennedy Space Center, in Cape Canaveral, Florida, where a two-hundred-foot rocket sat fueling up at Launch Complex Number 41, preparing to blast off two days later, carrying the Curiosity rover to Mars. It was a small gathering of colleagues who had just learned of the untimely death of biologist Lynn Margulis on November 22, 2011. We would all miss her funeral because of the imminent launch of Curiosity, so we congregated that evening over curry and saag to tell stories about Lynn, laugh, cry, and feel that bond we humans share when a person crosses over from sharp individual existence to the more diffuse persistence of collective influence, memory, and love, her microbiota shuffling off in search of other mortal coils, new living collectives to animate for a while. At such moments, we glimpse something that Lynn helped us learn: that our own individuality is a brief illusion transcended by love and biology. The handful of women and men who convened that evening, NASA übernerds all, had our lives enriched by Lynn’s incandescent intellect and nurturing heart. She seemed timeless and tireless, and she died suddenly, felled by an aneurism at the age of seventy-three. So we shed those aqueous, saline tears for Lynn, who in some way had changed all of us, and who had done so much to shape our ideas about planets and life.

  Lynn Margulis was a giant of modern biology, but she was also more than that: she braved the boundary between science and philosophy, fearlessly applying rigorous science to problems that changed the way we think about profound questions of self and identity, and the limits of current scientific knowledge and methodologies. Her theory of endosymbiosis, controversial at first and now enshrined in biology textbooks, showed that in evolution, radical cooperation is just as potent a force as deathly competition. One great example involves mitochondria, the tiny micron-size power plants inside our cells. According to endosymbiotic theory, these used to be freely living bacteria that joined our ancestral cells in a mutually beneficial, symbiotic, relationship. The association became so tight that eventually the partners joined together to form a new kind of organism. In fact, Lynn taught us that many of life’s most important evolutionary innovations resulted from assimilation, fusion of formerly separate individuals, the formation of cooperatives, and the sharing of genes and traits. Survival of the fittest still applies, but often the fittest are those assemblages of organisms that creatively merge into new kinds of individuals.

  Lynn Margulis, 2005.

  I had the pleasure of knowing Lynn for five decades. Her son Dorion Sagan, an accomplished science writer (also, I would say, a natural philosopher), became her longtime collaborator on several clever and important books that dazzle with literary and scientific brilliance. In the mid-1960s, Dorion and I, with our parents involved in the Bostonian scientific community, became fast friends at an early age. So I also got to experience some of Lynn’s style of mind nurturing. She was supportive, or at least tolerant, of our various ad hoc creative projects, experiments, and stunts, including some involving pyrotechnics that today would probably
have the neighbors calling Homeland Security. She was awfully busy, and not always around, but occasional outings with her to places like science museums were thrilling. She spoke to kids as if they could understand adult concepts, which they generally can. I still remember puzzling over something she said about metabolism when I was, oh, probably ten.

  It is remarkable how many astrobiologists today remember Lynn as an essential mentor.3 Many also describe her as an old and valued friend. She had an outsize influence on the development of exobiology, and then astrobiology, at NASA, lending her biological wisdom and perspective to an agency heavily biased toward physical science.

  Many people have heard of the Gaia hypothesis, which Margulis formulated, along with Jim Lovelock, in the 1970s. As a concept, it has often been abused as a New Age catchall, or mistakenly derided as pseudoscience, but at its core is an insight about the relationship between planets and life that has changed our understanding of both. In his work toward finding life on Mars, Lovelock realized that life must be, inherently, a planet-altering phenomenon. So he and Margulis, chemist and biologist, applied their collective symbiotic mind to the question of what life does to its environments. In exploring this question, they realized that the distinction between the “living” and “nonliving” parts of Earth was not as clear-cut as we thought. Lynn added her focus on the role of cooperative evolutionary networks in biological systems. Studying Earth’s global biosphere together, they realized that it has some of the properties of a life form. It seems to display “homeostasis,” or self-regulation. Your own internal homeostasis maintains your temperature, the pH of your blood, and a wide range of other properties within an optimum, healthy range that keeps you alive. Many of Earth’s life-sustaining qualities exhibit remarkable stability. The temperature range of the climate; the oxygen content of the atmosphere; the pH, chemistry, and salinity of the ocean—all these are biologically mediated. All have, for hundreds of millions of years, stayed within a range where life can thrive. Lovelock and Margulis surmised that the totality of life is interacting with its environments in ways that regulate these global qualities. They recognized that Earth is, in a sense, a living organism. Lovelock named this creature Gaia.

  Margulis and Lovelock showed that the Darwinian picture of biological evolution is incomplete. Darwin identified the mechanism by which life adapts due to changes in the environment, and thus allowed us to see that all life on Earth is a continuum, a proliferation, a genetic diaspora from a common root. In the Darwinian view, Earth was essentially a stage with a series of changing backdrops to which life had to adjust. Yet, what or who was changing the sets? Margulis and Lovelock proposed that the drama of life does not unfold on the stage of a dead Earth, but that, rather, the stage itself is animated, part of a larger living entity, Gaia, composed of the biosphere together with the “nonliving” components that shape, respond to, and cycle through the biota of Earth. Yes, life adapts to environmental change, shaping itself through natural selection. Yet life also pushes back and changes the environment, alters the planet. This is now as obvious as the air you are breathing, which has been oxygenated by life. So evolution is not a series of adaptations to inanimate events, but a system of feedbacks, an exchange. Life has not simply molded itself to the shifting contours of a dynamic Earth. Rather, life and Earth have shaped each other as they’ve coevolved. When you start looking at the planet in this way, then you see coral reefs, limestone cliffs, deltas, bogs, and islands of bat guano as parts of this larger animated entity. You realize that the entire skin of Earth, and its depths as well, are indeed alive.

  Lynn Margulis’s influence on science will continue to emerge and dazzle gradually. When she left this earth, our global mind, our noösphere, lost one blazing neuron, which, during its time, sparked great thoughts that linger. She challenged us to rethink our cozy established ideas, definitions, narratives, and categories of living things, and she changed the way we see life, evolution, our planet, our cells, ourselves. Recently the science news is full of stories of the “microbiota,” detailing how you and I are mostly microbes, with the bulk of our biomass and metabolism, in sickness and in health, dominated by the complex ecologies within us. Lynn was always telling anyone who would listen, “You are not an individual. You are a community.” The discovery of the human microbiota is redefining what it means to be human and how we relate to the rest of life. When I read about this unfolding revolution, I think, “Yes, this is where Lynn was pointing us all along.”

  What Does Earth Want?

  The acceptance of the Gaia hypothesis was, and remains, slow, halting, and incomplete. There are several reasons for this. One is just the usual inertia, the standard conservative reluctance to accept new ways of thinking. Yet Gaia was also accused of being vague and shifting. Some complained that the “Gaians” had failed to present an original, well-defined, testable scientific proposition. How can you evaluate, oppose, or embrace an idea that is not clearly stated, or that seems to mean different things to different people? There was certainly some truth to this. Gaia has been stated many different ways. Also, it didn’t help that Margulis and Lovelock were more than willing to mix science with philosophy and poetry, and they didn’t mind controversy; in fact, I’d say they enjoyed and courted it.

  Gaia, subversively, blurs the boundaries between the scientific and the nonscientific. This may be one of its most valuable aspects, but is also a big reason that the scientific establishment has had so much trouble with it. Saying that “Earth is alive” is, of course, asking for it. The statement is both true and not true, profoundly insightful yet subject to infinite reinterpretation, and not a scientific statement that can be tested.

  Yet Earth does have previously unrecognized qualities that make it more like a living organism than we once knew. It seems to exhibit self-regulation arising from the collective interactions of numerous component systems. But you would not confuse it with any other entity we considered to be an organism. It has never reproduced.* It’s been “alive” for billions of years. It also happens to be a planet. So why even ask if Earth is an organism? Well, are you an organism? You probably like to think so, but like Earth, you’re also essentially a community of interacting parts, many of which are themselves organisms and some of which are not made of living cells. Whether or not you have reproduced, your DNA molecules are billions of years old and will be quasi-immortal for a long while, at least as long as Earth life lasts.* Now think of parasites living their whole life in the body of their host, or bacteria living in your gut, unaware that their “world” is a living organism and that their survival depends on the maintenance of an environment that is synonymous with the health of that organism. Are we not like such dependent bacteria living within our host, Gaia? If it induces such thoughts, then the hypothesis is not only controversial, but useful. It gets us to consider what we really mean by “living” and “organism.”

  A more science-y phrasing of the hypothesis would be something like “The sum total of life on Earth interacts with other planetary subsystems to form a complex, self-regulating entity that maintains conditions within which life can continue to thrive, and that is observable in terms of the stable, nonequilibrium composition of the atmosphere and other environmental variables.” This, however, is rather ponderous and unpoetic compared to “This planet is alive and we’ll call it Gaia.”

  Does Gaia have a sense of purpose? A big stumbling block to widespread acceptance of the Gaia hypothesis came over the question of teleology. A teleological explanation is one that justifies the way something is by invoking its functional purpose, as in “These boots have heels because they were made for walking.” The notion that Gaia, the living planet, has some sense of purpose was seeded in the early papers of Margulis and Lovelock: their first published paper on the topic was called “Atmospheric Homeostasis by and for the Biosphere.” The “by and for” is what caused all the hubbub—not so much the by, which merely suggests that it is the biota that do the self-regulation, but the f
or, which seems to imply that Gaia is not only living but also serving, and perhaps also seeking, that Gaia is trying to optimize conditions on Earth for life.

  Many of the arguments about Gaia became stuck on this aspect. Lovelock and Margulis probably lost a lot of potential supporters because of the (to many) apparent fallacy of teleology. In later statements they backed off on this aspect, claiming that they had been misunderstood and had never meant to imply conscious control by the biosphere. I think there was more to it, though.

  At first I thought of the teleological language as somewhat annoying overreach on their part, language that muddied the waters. Now I’m not so sure. Anyone who knows and has followed Lynn and Jim knows that both relished their status as iconoclasts who shook up the world of science with their disturbing ideas. Lovelock in particular has cultivated his position as misunderstood scientist on the fringe. So, I also had the sense that there was deliberate obfuscation here, and that really, maybe a little, they were both toying with us.

  There’s a trickster element to this line of argument—that Gaia is seeking something, not merely exhibiting stabilizing behavior that arises out of the complex interactions of a global geobiosystem, but acting on its own behalf, with life taking care of life because it wants to—because the more you think about it, if you really think about it, this starts to mess with our notions, our assumptions, about consciousness and intentionality.

  Just as we should question how Gaia could be considered to want anything, to possess any kind of desire or direction, we should ask the same thing about a human brain. Of Earth, we can ask: how can this system of interacting parts, each clearly without conscious intent, following physical laws and evolutionary processes, be said to manifest conscious intentionality? Then, with the next thought, using all the concentrated neuronal intensity we can muster, we can ponder the exact same mystery about our own thoughts and intentions. Here in our heads, the physical parts are not evolving populations of organisms and landscapes, volcanoes, chemical cycles, rivers, forests, and reefs. Rather, in the brain, the interacting components are populations of neurons with ions migrating in and out of their dendritic branches, chemical flows of neurotransmitters, and shifting patterns of networks and connections. So here, too, we can ask: how can this system of interacting parts, each clearly without conscious intent, following physical laws and evolutionary processes, manifest conscious intentionality?