Light of the Stars

by Adam Frank

  The point here is that all of these processes are fundamentally transformations of energy. The presence of an atmosphere turns solar energy into motion energy as air rises and falls. With water or CO2 in the atmosphere, the energy of motion feeds into the energy associated with evaporation and condensation. Weathering and the breaking of chemical bonds in rocks is yet another form of energy transformation. So, even without life, a planet can take its sunlight and use it for ever more complex work, driving change, evolution, and innovation.

  Thinking this way about evolution and energy led Marina Alberti, Axel Kleidon, and me to propose a new classification for planets.17 While the Kardashev scale focused on the total energy falling onto a planet, we were interested in what happens to that energy once it gets within a planet. Here, “within” doesn’t mean underneath the surface of a world, but within the coupled planetary systems. What happens when a sun’s energy, in the form of incoming light, feeds through the linked networks of atmosphere, hydrosphere, and so on, including a biosphere?

  Unlike Kardashev, our goal in making a new planetary classification scheme was not detection (though it proves useful for this). Instead, we wanted to use the laws of physics, chemistry, and biology on planetary scales to see where planetary evolution might lead. In particular, we wanted to use the planets we already understood to map out the properties of the ones we don’t understand—the planets with sustainable civilizations.

  Working together, the three of us saw that the universe’s vast census of planets might be grouped into a spectrum of five main classes.

  An airless world like Mercury is a Class 1 planet in our scheme. The transformations of sunlight are simple, and so the degree of work that is done and the complexity generated are limited. Class 1 planets are truly dead worlds.

  A world with an atmosphere but no life, like Mars or Venus, is a Class 2 planet. The flow of gases and liquids driven by sunlight represent work being done within the planetary systems. That work can make things happen on a range of time scales, like the daily appearance of fog or the yearly appearance of dust storms.

  Class 3 planets are those with what we called a “thin” biosphere. These are worlds where life has gotten started. It’s affecting the rest of the coupled systems, but does not yet dominate these systems. One way to quantify this is to look at what’s called the net productivity of a planet, meaning how much energy its biosphere harvests. Donald Canfield has estimated the net productivity of the Earth’s early Archean biosphere and found that it was a hundred times smaller than today.18 So Earth during the Archean was a Class 3 world. If Mars had life during its wet Noachian period, four billion years ago, then it too might have been a Class 3 world.

  Class 4 planets, on the other hand, have been hijacked by life. They have “thick” biospheres that are deep networks of animal, plants, and microbes, all feeding on each other and all feeding back onto the other planetary systems. The existence of our oxygen atmosphere, created in the Great Oxidation Event, tells us that we are living on a biosphere-dominated planet where life plays an outsized role in planetary evolution. So the Earth, before civilization appeared ten thousand years ago, was a Class 4 world.

  Our scheme was based on the fact that we had real examples of the first four planetary classes. Through these known worlds, we could understand how solar energy feeds through the planetary systems and drives evolution. That knowledge gave us purchase to see something essential about our hypothesized fifth class: a world hosting a sustainable civilization.

  Going from Class 1 to Class 4 worlds, we see an increase in the complexity of their energy flows and transformations. Class 1 worlds could do little in terms of turning solar energy into work and change. Class 4 worlds comprised rich networks of processes channeling solar energy into work and change. From the perspective of thermodynamics, we could see how planets in each successive class had “found” new ways to transform their incident starlight into evolution. On a world without life, this evolution can be rich, but the pathways are constrained purely by physics and chemistry. In a sense, its details are fairly predictable. Once life appears in Classes 3 and 4, biological evolution takes over. Life figures out entirely new ways to do work, yielding new processes that feed back on the rest of the planet.

  The relationship between complexity, work, and energy flows gave us a key to understanding what our fifth class of planet might look like. A thick biosphere on a Class 4 world channels more energy into work than a thin biosphere on a Class 3 world, which itself channels more energy into work than on a Class 2 world. That means a planet with a sustainable civilization—a Class 5 world—might be even more adept at wringing work and change out of sunlight. On a Class 5 planet, the biosphere—which now includes a globe-spanning civilization—becomes even more productive than Class 3 and Class 4 worlds. The civilization not only harvests more energy, as Kardashev imagined, but also figures out how to put this energy to work in ways that do not push the planet into dangerous territory. The civilization, as part of the biosphere, adds what philosophers call “agency.” The civilization makes choices with goals in mind. Thus, Class 5 planets have agency-dominated biospheres. The civilization is now deliberately working with the rest of the natural systems to increase the flourishing and productivity of both itself and the biosphere as a whole.

  Perhaps the civilization converts its planet’s deserts into productive ecosystems. Such “desert greening,” if done correctly, could stabilize a changing climate. Or it might engineer plants that can both photosynthesize and produce electricity (there are researchers studying this now).19 Or it might cover regions with solar cells in ways that also increase (or at least don’t decrease) the total biospheric productivity and health of the planet. The possibilities are rich, and our study was meant only to suggest the right direction a Class 5 agency-dominated biosphere might take. There is much fruitful work to be done in turning the basic concept of Class 5 worlds into strategies for the future.

  So, where does Earth fit into our classification scheme right now? As we enter the Anthropocene, we are clearly leaving the Class 4 state. Our activity and choices are strongly modifying the state of the biosphere and other planetary systems. But we are making these changes without a long-term plan, as planetary scientist David Grinspoon and others have pointed out.20 We are evolving the planet toward something new, but we can’t say if that novel state will include us in the long term. So, Earth at the beginning of the Anthropocene is no longer a Class 4 world but is not yet, and may never be, a Class 5 planet. As of now, it’s a hybrid world. It’s evolving toward something other than it was, and it’s doing so in a way that’s dangerous for our project of civilization.

  The key point in developing these five classes of planet was the necessity of putting civilizations back into the context of the biosphere, rather than above it. From this perspective, sustainable civilizations are extensions of the long process of planetary evolution. Biospheres without civilizations are already agents of novelty. From oxygen-producing microbes to grasslands to megafauna (like wooly mammoths), they produce new things that then enter into the web of positive and negative feedbacks on the planetary system as a whole. The great lesson of Lovelock, Margulis, and their Gaia theory was that the biosphere could evolve feedbacks that kept the system stable. A sustainable agency-dominated biosphere should be no different.

  After his pioneering work on the biosphere, Vladimir Vernadsky went on to consider the possibility of planets “waking up” via what he called a “noosphere.” Coined from the Greek noos, for intelligence, a noosphere was a shell of thought surrounding the planet. It was the result of a biosphere evolving creatures that could think and develop technology. From geology to life to mind, the emergence of the noosphere was, for Vernadsky, a next stage in planetary evolution.21

  Class 5 planets might be seen as worlds that have evolved a noosphere. The pervasive wireless mesh of connections that constitute today’s internet has already been held up as an initial version of a noosphere for Ear
th. Thus, we might already make out the contours of what a sustainable world will look like. To truly come into a cooperative coevolution with a biosphere, a technological civilization must make technology—the fruit of its collective mind—serve as a web of awareness for the flourishing of both itself and the planet as a whole.

  Beyond the Kardashev scale’s focus on energy as the currency of planetary dominance, we now encounter an essential lesson the stars might teach us about our next moves. Planets are engines of innovation. But, from Class 1 to Class 4, those innovations are blind. They are the result of pure chance and pure mechanics—the laws of physics, chemistry, and biological evolution. They do not have an end in mind. There is no teleology.

  Recall that one of the loudest criticisms of Gaia theory was that it could be interpreted to imply that life on Earth “wanted” to steer the planet in some direction. It was in response to these criticisms that Gaia morphed into the less controversial Earth systems theory. There, evolution was once again blind. But when a civilization emerges and triggers its own version of the Anthropocene, the age of blindness must come to an end.

  In the deepest sense, Class 5 planets would represent the completion of Gaia. They would be worlds where the planet as a whole has an evolutionary direction, a goal. That is what an agency-dominated biosphere means. The civilization, working for its own continued existence, recognizes itself as an expression of the biosphere and chooses a direction.

  So, we cannot bring the world to heel. Instead, we must bring it a plan. Our project of civilization must become a way for the planet to think, to decide, and to guide its own future. Thus, we must become the agent by which the Earth wakes up to itself.

  THE WAY FORWARD

  Ultimately, the problem we face is confronting a twenty-third-century dilemma armed only with a thirteenth-century mind. Our project of civilization has been successful on scales we could not have imagined when we began it ten millennia ago. But with that success has come consequences that will last for centuries.

  Across the long history of our project, we didn’t know our true place in the universe and could not, therefore, know our place within the planet’s own evolution. But now, through science, we can see a new truth. The Earth is but one world among trillions, and we are not a one-time story. Now we can—and must—make this our story. We must make it the human story, one that cuts across cultures, nations, and politics.22

  We are, most certainly, not the first species that has dramatically changed the Earth’s climate. It has happened before, and we can see how that story played out in the past. Earth is possibly, and even likely, not the first planet that has evolved a civilization. Using all we have learned about planets, we can see how that story, including climate change, might also have played out in the past.

  But what the Anthropocene means for the planet, and what it means for us, are different things. If we continue to do nothing about our use of fossil fuels and the other drivers of the Anthropocene, it is more than conceivable that we’ll push the planet into domains that prove difficult for our kind of complex global civilization. If our project of civilization collapses for a time, or even permanently, the Earth will happily move on without us. In that sense, our urgency in dealing with climate change and the Anthropocene has nothing to do with “saving the planet.” Our entry into the Anthropocene shows that our project of civilization has now become its own kind of planetary power. It’s a new story we have to tell about ourselves, and everything now depends on learning and acting upon it.

  Across the pages of this book, we’ve assembled this new narrative through smaller stories of that story’s own evolution. We have encountered heroic scientists who took us up to the mountain so that we might see farther. There were Frank Drake, Jill Tarter, and Nikolai Kardashev, who braved the scorn of their colleagues to take the existence of exo-civilization seriously as a topic for scientific inquiry. Through their efforts, we could begin to see life and the stars in a new light. There were explorers like Jack James and Steven Squyers, blasting robots across space to the other worlds in our solar system. Through their work and the studies of researchers like Robert Haberle, we learned the laws of climate and evolution for all planets. Army corpsmen and scientists like Willi Dansgaard braved Camp Century on Greenland’s ice sheet to help us see more deeply into the transitions of Earth’s climate. Then came people like Donald Canfield, who traveled the world to unpack the deep history of our planet and its life. Putting all this together were visionaries like Vladimir Vernadsky, James Lovelock, and Lynn Margulis, who lifted our sights to see how that life can partner with its planet to evolve into something greater, something more. Finding other planets was the job of scientists like Michel Mayor, Bill Borucki, Natalie Batalha, and others. Their work answered a millennia-old question and, in doing so, filled the night sky with a trillion trillion worlds and possibilities. And finally, appearing at almost every turn, there was Carl Sagan. More than almost anyone else, we owe the possibility of this new story to his genius.

  Science has given us a new perspective, a new vision, and a new story that can help us find a way forward as we face the challenge of the Anthropocene. But this can only happen if we listen carefully and truly make this new story our own.

  It is time to grow up.

  The central argument of this book, and one that Carl Sagan already understood, is that humanity and its project of civilization represent a kind of “cosmic teenager.” We are likely just one world among many that has grown a civilization to the point where it has gained power over itself and its planet. But, like a teenager, we lack the maturity to take full responsibility for our ourselves and our future.

  Gaining the astrobiological perspective is the first, essential step in our maturation and our ability to face the Anthropocene. It means recognizing that we and our project of civilization are nothing more than the fruit of Earth’s ongoing evolutionary experiments. Any civilization on any planet will be nothing more than an expression of its home world’s creativity. We are no different from those we would call “alien.”

  So our focus has to shift. It’s time to leave the tired question, “Did we create climate change?” behind. In its place we must take up our bracing new astrobiological truth: “Of course we changed the climate.” We built a planet-spanning civilization. What else would we expect to happen?

  But we should also recognize that creating climate change wasn’t done with malevolence. We are not a plague on the planet. Instead, we are the planet. We are, at least, what the planet is doing right now. But that is no guarantee that we’ll still be what the planet is doing one thousand or ten thousand years from now.

  As children of the Earth, we are also children of the stars. If nothing else, the Anthropocene can make that fact as real to us as the shriek of a howling storm, the oppressive heat of a desert landscape, or the cool silence of a deep forest. Through the light of the stars, through what they can teach us about other worlds and the possibilities of other civilizations, we can learn what path through adolescence we must take. And in that way, we can reach our maturity. We can reach our full promise and possibility. We can make the Anthropocene into a new era for both our civilization and the Earth. In the end, our story is not yet written. We stand at a crossroads under the light of the stars, ready to join them or ready to fail. The choice will be our own.

  ILLUSTRATION CREDITS

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  Alan Dunn The New Yorker Collection/The Cartoon Bank

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  © Frank Drake

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  © NASA

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  © Bettmann/Getty Images

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  © NASA

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  © W. Robert Moore/National Geographic/Getty Images

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  © NASA

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  Sputnik/Science Photo Library

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  Photo courtesy of the Estate of Lynn Margulis

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  © Acey Harper/the LIFE Images Collection/
Getty Images

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  Courtesy of the Archives, California Institute of Technology

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  David Nunuk/Science Photo Library

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  © Byurakan Observatory

  ACKNOWLEDGMENTS

  This work would not have been possible without the support and, sometimes, direct intervention of some very smart and kind people. I must first thank Howard Yoon of Ross Yoon Agency for his working so closely with me to develop the early versions of the idea into a coherent form and his many years of help in so many, many ways. From the very beginning, my editor at W. W. Norton, Matt Weiland, saw how to make the idea and its incarnation into this book cleaner and more sharply defined. It was a great pleasure to work with him and I am deeply grateful that his skills were brought to bear on this project. Simply put, he is a great editor. I am also grateful to have had Remy Cawley on the W. W. Norton team. In editing, copyediting, and managing the image process, her precision and thoroughness were essential. I was also lucky to have two wonderful University of Rochester undergraduates working with me as assistants on the book. Molly Finn worked tirelessly on fact checking and accumulating proper references and reference forms. Elise Morgan endured a crazy autumn tracking down images and permissions. Both showed remarkable skills for young scholars, and I was lucky to have found their help.