Dr. David Grinspoon, Senior Scientist for Astrobiology Strategy, NASA

Tracing life’s history through an astrobiological lens can provide valuable perspective on the global changes and challenges facing us today. Many of the same technological developments which have allowed humans to thrive globally, and to dangerously alter our planet, have also allowed us to launch satellites into space, and thus to observe and monitor these changes. Without this new power of self-observation, we would not have a fighting chance of making the corrections necessary to make wiser choices about how we live on this planet. Beyond Earth observations, exploration of other planets has delivered vital new knowledge applicable on our home planet. For example, studying the atmospheres of Venus and Mars has provided crucial insights into climate change. There are many concrete examples of space technology advancing sustainability, but I will focus more here on the gift of perspective provided by my field of Astrobiology, which seeks to understand the prevalence and distribution of life in the universe.

The perspective of Astrobiology is one of deep space and deep time. The deep space perspective is one of plenitude, humility and wholeness. We have learned that our location in the universe, at least in terms of physical position, is nothing special, and that planets are more abundant than we can comprehend.

Carl Sagan spoke of the “great demotions” through which science has put humanity in its place, by successively undermining the ways in which we had once seen ourselves as central and important in the story of the universe (Sagan, 1994). Arguably, the realization that we are now in the “Anthropocene,” that our agency, or lack thereof, has allowed us to become unwitting planet changers, has recast this narrative. Perhaps we are, after all, significant players in the story of the Earth. The Anthropocene is the proposed name for the epoch of geologic time we have now entered, characterized by human-driven planetary-scale changes. By recognizing and naming the Anthropocene are we in effect reversing things and giving ourselves a “great promotion”?

Perhaps. But it is questionable whether this is really such a great honor to bestow upon ourselves, for we don’t know whether ultimately we are to be planet wreckers or planet savers. Strangely, we may have to choose between these two. By becoming agents of planetary change we may have lost the option of remaining merely innocent bystanders or bit players in evolution.

Yet how much agency do we really have if we can’t obviously choose our role in Earth’s story? We seem to have agency on certain small scales of organization. We are obviously very skilled at building machines and organizing activities that cumulatively act to change our world. So, we are acting at a global scale. Yet have we shown agency or intentionality on that planetary scale? Arguably, yes, we have. There are examples of global-scale efforts to fix environmental problems, such as the Montreal Protocol, which is more or less on track to successfully repair the damage we’ve done to Earth’s protective stratospheric ozone layer. Other examples from the realm of global health show that planet-wide efforts can eradicate deadly diseases. Yet the most concerning planetary changes being caused by humans do not result from globally coordinated efforts or plans but rather from accidental concatenations of more localized and short-term decisions. If we, global humanity, have agency over our planetary-scale impact it is – so far at least – limited and tentative. Thus, perhaps that “great promotion” toward recognizing our importance in the current chapter of Earth history should be felt not as a pat on the back but more of a kick in the rear. If we want to translate our significance into something to be proud of then we have some work to do.

The search for identifiable biosignatures on other planets is requiring us to understand life as a component of a larger physical system. In the 1970s scientists working on the first life detection spacecraft mission to Mars realized that we might recognize life on a planet simply by observing its perturbing effects on the planet’s atmosphere. After all, Earth’s atmosphere, heavily oxygenated by life, is drastically different from what we would expect on a lifeless Earth. This insight was also the origin of the Gaia hypothesis, the idea that life should be understood as a planetary-scale phenomenon, so deeply embedded in the cyclic behavior of our Earth that the distinction between the living and nonliving components is difficult to discern and perhaps illusory (Margulis and Lovelock, 1974). Today we have learned that planets are abundant throughout our galaxy. As we are building new telescopes to search for the signs of life on exoplanets, the notion of planetary-scale life is essential to this quest. It is in finding biological perturbations breathed into the atmospheres of these worlds by our cosmic brethren that we invest our hopes of finding them.

Astrobiology has allowed us to see ourselves, and our biosphere, as fundamentally and deeply entwined with other planetary systems. The contrast between living and lifeless planets drives home to us that we are not discrete organisms living on an otherwise dead world, but parts of a grand cyclic planetary scale biosphere, exchanging matter and energy with our environment and with other living systems. This perspective can help us to see our current global environmental challenges as more than just momentary technical puzzles to be solved. Rather the challenge is to fundamentally reimagine our role in Earth systems. In order to build a healthy technosphere we will need a deepened understanding of the relationship between planet and life – between Earth’s biosphere and its other physical systems – so that we can learn to work with the Earth instead of against it, to gracefully integrate our global scale activities within these systems.

The deep time perspective also promotes humility, and identification with a larger whole. As an astrobiologist I am fascinated by the major historical transitions in planetary evolution and how they reflect the evolving relationship between planet and life. This informs my view of recent debates over the Anthropocene. How does our time fit into the larger narrative of planetary evolution?

In our quest to understand how life fits into the story of the universe, we’ve traced our existence back to the earliest signs of life on Earth, 3.5 to 3.8 billion years ago, and life’s inferred origin perhaps 4 billion years ago. We’ve followed the story back to the origin of our planet itself in a flurry of energetic collisions 4.5 billion years ago and all the way to the birth of our universe, which exploded into being from a singularity of nothingness about 13.8 billion years ago.

In a certain sense our appearance here is astonishingly ephemeral compared with the timescale of cosmic evolution. As individuals our existence is fleeting, and even our tenure as a genus or a species, hundreds of thousands to millions of years, is incredibly brief measured against geological or cosmic time. However, if we choose to identify with our biosphere, with “Gaia”, then this can radically change our temporal perspective. We, Gaia, have been here for about 4 billion years. We have been here for nearly one third of all time. That is something. Yet we have quite recently begun behaving, and altering our planet, in wholly unprecedented ways.

Many scientific discussions of the Anthropocene have focused on the debate over when it began. However, that obscures perhaps the most interesting and crucial question raised by the transition to a largely human-altered planet: When and how will it end? What will the Anthropocene ultimately be in Earth history? Viewed from some future deep-time perspective will it have been a momentary event (like the Cretaceous/Paleogene boundary 65 million years ago, marked by the centimeter thick layer of fallout from the dinosaur-killing asteroid), a prolonged interval (like the Paleocene Epoch that lasted from 66 to 56 million years ago), or could it actually become something even more significant?

I suggest that this transition may not be, as proposed, merely an Epoch boundary, but something much rarer. Epoch boundaries are a frequent occurrence throughout Earth history. Epochs are the relatively thin and numerous layers usually drawn toward the right side of the geological time scale. Their boundaries are often characterized by episodes of global change and extinction events. Much more consequential are the boundaries separating the very long phases, called Eons, usually shown on the far-left side of this chart. Each of these represents a fundamental branching point in our planet’s history. Our dynamic Earth has gone through many fluctuating changes, but geologists separate our planet’s long history into only four Eons, during which our planet’s character was fundamentally different from the others. I suspect we may now be at another of these pivotal moments, and our planet may be at the beginning of its 5^th Eon, which I have proposed we call the “Sapiezoic” (Grinspoon, 2016).

The first Eon was pure hell. All the planets started with conditions hostile to any kind of life, with leftover debris from planet formation crashing down from space, erratically smashing, churning and heating their surfaces, making red-hot atmospheres first of vaporized rock and then of boiling steam. In recognition of these conditions, Earth’s first Eon is named the Hadean. All that we’ve learned about the violent, collisional nature of planetary origins suggests that each rocky planet started off with its own private Hadean. Eventually, the cosmic pounding subsided and the steam turned to rain which filled the oceans.

The transition to Earth’s second Eon, the Archean, came around 4 billion years ago, and corresponds roughly to the arrival of stable habitable conditions and the origin of life. Although we are still testing our hypotheses with ongoing and planned missions of exploration, our nearest neighbors, Venus and Mars seem to have both experienced transitions to conditions similar to those which enabled an origin of life on Earth, including geologically active surfaces and warm, organic-rich seas. Such a phase may be common for rocky planets at the right distance from their stars, and life might possibly have begun on all three of these planets. Apparently only on Earth did a robust, long-lived, global biosphere develop and become a permanent, planet-altering feature. The transition to the Archean Eon was when Earth diverged from the path of a lifeless planet. Since then, biology has been a major driver of geologic change.

The extent of biological influence on our planet is still being discovered. Beyond obvious anomalies such as an oxygenated atmosphere, ozone layer, and continents whose reflective properties and cloud cover are greatly altered by forests, Earth’s topography, mineral diversity, and perhaps the material properties of its interior, have been altered by life’s infiltration into its physical and biogeochemical cycles. As astrobiologist Colin Goldblatt has said: “The distinguishing characteristic of Earth is planetary-scale life.”

We don’t know exactly how or when Earth went from being a dead planet graced by some organisms to a planet thoroughly permeated with life, but certainly by Earth’s third Eon, the Proterozoic, Earth could be described as a living world. The beginning of the Proterozoic, 2.5 billion years ago, corresponds roughly to the Great Oxygenation Event when, chemically, life took over. In discovering solar energy, photosynthetic bacteria began to flood the atmosphere with oxygen, a poisonous gas that caused mass extinction, but also created the chemical conditions for animal respiration and the protective ozone layer that allowed life to leave the oceans and colonize the land.

Then, 540 million years ago came the “Cambrian Explosion” – the sudden appearance of a myriad of complex, multicellular animal and plant life forms, including the body plans of basically all modern animals. This enabled, among many other things, the evolution of intricate nervous systems, elaborate behavior and learning. This burst of biological innovation is recognized as the beginning of the fourth and (so far) final Eon of Earth history – the Phanerozoic Eon, which continues to this day.

These four Eons of Earth history are each distinguished by a different role for life on the planet, and each Eon boundary represents a major shift in the relationship between life and the planet. The origin of life, the “oxygen catastrophe” and the origin of complex multicellular life each resulted in a permanently changed planet.

Now, this saga has reached the pivotal moment when humans have become a dominant force of planetary change, and geological and human history are becoming – perhaps irreversibly – conjoined. As a result, we are witness to, and party to, the advent of a radically new type of global change: Self-aware cognitive/geological processes (Grinspoon, 2016; Frank et al., 2022).

Now that cognitive systems have gained a powerful influence on the planet, we are observing the effects of not only a new geologic force, but a new type of geologic force – one becoming aware of its own influence. I believe that the beginning of a time when self-aware cognitive processes become a key part of the way the planet functions is potentially as significant as the origin of life and the pivotal changes marking the other Eon boundaries in Earth history.

Yet, in order to qualify as the start of a new Eon, such a transition would also require extreme staying power. Eons typically last for at least hundreds of millions of years. Even if we accept that this new force represents a sufficiently radical break from the past – a fundamentally new phase in the planet/life relationship – can it possibly persist for such an interval?

Questions of civilization persistence over geological or cosmological timescales are familiar to theorists in the field of SETI (the Search for Extraterrestrial Intelligence), who have long recognized that the number of technological civilizations in the universe must be proportional to their average longevity (Bracewell, 1974). The literature of this field contains discussion of the potential longevity not just of human civilization, but of human-like civilizations elsewhere in the galaxy. What do we mean by “human-like?” That is a wonderful question which connects our essential nature, our exceptionalism compared to the rest of life, and our role on the planet. Can we, or can any technological civilization, persist for geologically meaningful timescales? Can a civilization become integrated into the cyclic functioning of its planet in a robust way, as life did on Earth (but apparently not on Venus or Mars) long ago?

For the Anthropocene to become the first epoch of a new Sapiezoic Eon would require a permanently changed planet in which cognitive processes become, as life did by the end of the Archean, a long-term stabilizing component of a functioning planet. This implies a radically different mode of interaction with the planet than is currently being exhibited by “intelligent” technological life.

The success of technological societies in increasing their populations and expanding their habitats and environmental reach can produce positive feedbacks which create instabilities and threaten catastrophe. The most basic imperatives of biological evolution (reproduction and survival) are likely to replicate this pattern on other planets with global biospheres which develop complex, cognitively capable life. From a systems perspective, the early stages of a cognitive planetary transition are arguably highly unstable because global influence will likely always precede global awareness and self-control. Hence the dangers of our current “Anthropocene dilemma” (Grinspoon, 2016) where, like mindless automatons at the controls of a complex vehicle, we are a danger to ourselves because the scale and scope of our power exceeds that of our awareness.

However, conscious awareness of self-induced threats can initiate stabilizing negative feedbacks. Consider the stratospheric ozone depletion which arose as an unintended consequence of new technology. This threat to terrestrial habitability was recognized, studied and deliberated. Now, through global agreements it is being successfully mitigated, and serves as an illustrative example of the stabilizing negative feedback that can arise from self-recognition by global technological actors. Such examples suggest there are pathways by which cognitive geological processes could become a very long-lived and even permanent part of the Earth system.

Global technological influence clearly contains both peril and promise. Several scholars have described our near future as a bottleneck of technological adolescence and self-ignorance (Rees, 2003; Wilson, 2002). This implies that although we may not survive, we could also potentially get a handle on ourselves and learn to use our technology in ways that enhance, rather than threaten our survival. Our increasing powers of global influence are fundamentally unpredictable, but contain the potential for ruin & triumph, for existential threat as well as for circumventing natural and artificial disasters. The latter would require that we achieve a deep understanding of, and mastery over, both self and nature. In other words, it would require both technical and spiritual progress.

Are similar challenges likely to be faced by complex life elsewhere reaching a stage where cognitive processes become planetary processes? If so, then the technical, ethical and even spiritual choices and dilemmas facing extraterrestrial civilizations may resemble our own in some respects.

One does not have to be optimistic about humanity’s chances to see that the likelihood of such technological bottlenecks, if they can ever – even very rarely – be navigated – implies the possibility of a very different kind of planetary entity: An extremely long-lived technologically enhanced biosphere.

How might this vision affect the way we view our own future? It reframes our task. And it puts our immediate challenges over the next century (devising agricultural and energy systems that can provide for the needs of our population without wrecking the natural systems upon which we depend) against the backdrop of a much longer term challenge: Once we get over the short term (century scale) threat of destabilizing fossil-fuel induced climate change, we need to learn how to become a long-term stabilizing component of the planet. This will include: Over the next several hundred to thousand years, devising an effective asteroid and comet defense; Over the next several tens of thousands of years, learning how to prevent catastrophic natural climate changes, such as ice ages and intervening episodes of dangerous global warming; Over several billions of years we’ll have to find a way to compensate for the warming sun and prevent the otherwise inevitable runaway global warming that will result from the sun’s bright senescence. Or we’ll need to move.

The origin of life represented a fundamental branching point, setting our planet on a path distinct from those of our neighbors. The origin of self-aware intelligent geology may represent another. If a Sapiezoic transition is something that can happen to some planets then, as we explore the universe and begin to decipher the nature of exoplanets, we may find there are 3 kinds of worlds: dead, living and sapient.

How rare are sapient worlds? This depends on whether a species that develops world-changing technology can evolve culturally to a state where it can apply this power sustainably, in the service of its biosphere. The answer to this question will determine both our own future chance of survival and the likelihood of finding a long-lived technological phase on other planets. Thus, the central question of SETI is also the central question that confronts humanity about our own future. Can technological intelligence become something built to last?

Can humanity make it through the technological bottleneck? To do so would require us to re-invent ourselves, to find a way to operate cooperatively on a larger scale than we have done previously. A look at our deep history shows that we have found such capacities when the need arose. Homo Sapiens Sapiens arose in Africa between 200,000 and 160,000 years ago after our predecessors were nearly wiped out by devastating climate change. We survived by using sophisticated new technology that required language and new modes of cooperation to meet what would otherwise have been existential threats (Marean, 2010). It is our nature to invent, to cooperate in new ways, to survive. Our current dilemmas require the same skills applied on new temporal and spatial scales. We have done this before. Although right now we are in danger of initiating a mass extinction, if we get a handle on ourselves we could not only save our own civilization and call off the gathering extinction event but learn to prevent future asteroid impacts and ice ages. In the long run, by forestalling future mass extinctions and prolonging the life of the biosphere, we could be the best thing that ever happened to planet Earth.

When Carl Linnaeus, the Swedish botanist who invented modern biological taxonomy and nomenclature was looking for a name for the human species he chose Homo Sapiens, differentiating us from other primates by our quality of sapience, or wisdom. Perhaps this was overly optimistic. Or perhaps it was prescient. Whether or not we can live up to this name may depend on whether we can learn to gracefully integrate our technological prowess with the functioning of our planet, creating a Terra Sapiens. Nobody alive today will know whether we were able to begin this new Eon. We may not know for many millennia. But it gives us something to strive for.

References:

Bracewell, R.N. (1974). The Galactic Club. Intelligent Life in Outer Space. Freeman, San Francisco.

Frank A, Grinspoon D, Walker S (2022). Intelligence as a planetary scale process. International Journal of Astrobiology 21,47–61

Grinspoon, D. (2003) Lonely Planets: The Natural Philosophy of Alien Life. New York: Ecco/HarperCollins.

Marean, Curtis (2010). ‘When the Sea Saved Humanity’. Scientific American, vol. 303, no. 2, August 2010, pp. 54-61.

Margulis, Lynn and J. Lovelock (1974). “Biological Modulation of the Atmosphere”. Icarus 21: 471-89.

Rees, M. (2003). “Our Final Century: Will Civilization Survive the Twenty-first Century?”. William Heinemann (UK).

Sagan, C. (1994). Pale Blue Dot: A Vision of the Human Future in Space. New York, Random House, 1994.

Wilson, E.O. (2002). The Future of Life. Alfred A. Knopf.