Recent years have seen a vigorous debate over whether or not we have entered a new epoch of geologic time, the "Anthropocene," characterized by humanity as a new geologic force.
Much of this has centered over when this age began. Three candidates for this include: an "Early Anthropocene" many thousand years ago when humans first started large-scale modification of land and climate; the beginning of the industrial revolution with its CO2 emissions; and the nuclear test horizon. Choosing a single moment of origin may be less important than the realization that we are now in it. However, the debate has been fruitful, as all these candidates mark interesting steps in our journey from being just another primate to becoming a dominant geological force.
As a planetary astrobiologist, I am focused on the major transitions in planetary evolution and the evolving relationship between planets and life. I want to frame our current time as a stage in the cosmic life of our planet. What I wonder most about the Anthropocene is not when did it start — but when, and how, will it end? Will it end? Or is it possible that our own growing awareness of our role on Earth can itself play a pivotal role in shaping the outcome toward one that we would desire?
Although it has been proposed as a new epoch, we may in fact be experiencing something much more unusual. Picture the "geologic time scale" you've seen where the various phases of Earth's history are represented by a sequence of different layers corresponding to the rocks from different geological ages, with the most recent periods drawn at the top. New epochs are actually rather common in Earth's history. They typically last for millions of years. They are marked by the relatively thin layers in geological time. Their boundaries are often characterized by episodes of global change and extinction events. Much more rare and consequential are the boundaries, separating the longest phases, the billion-year-scale chunks of time called eons.
Geologists separate our planet's long history into only four eons. These represent fundamental branching points which each left the world permanently changed. I suspect we may now be at another of these pivotal moments, and our planet may be at the beginning of its fifth eon, which I propose we call the "Sapiezoic" (a hopeful, aspirational term meaning "age of wisdom"). Because what we are observing are the effects of not only a new geologic force, but a radically new type of geologic change. Never before has a geological force become aware of its own influence.
The first eon is named the Hadean because it was pure hell, with leftover debris from planet formation crashing down from space, erratically smashing, churning and heating Earth's surface, making red-hot atmospheres first of vaporized rock and then of boiling steam. Eventually, the cosmic pounding subsided and the steam turned to rain, which filled the first oceans.
The transition to Earth's second Eon, the Archean, came around 4 billion years ago and corresponds roughly to the coming of stable habitable conditions and the origin of life. Since then, biology has been a major agent of geologic change.
Earth's third eon, the Proterozoic, beginning 2.5 billion years ago, corresponds roughly to the Great Oxygenation Event when, chemically, life took over the planet. 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 complex, multicellular animal and plant life forms. This enabled, among many other things, the evolution of intricate nervous systems, elaborate behavior and learning. This explosion of biological innovation is recognized as the beginning of the fourth and final (so far) eon of Earth's history — the Phanerozoic Eon, which continues to this day.
Now, humans have become a dominant force of planetary change and, thus, we may have entered an eon of post-biological evolution in which cognitive systems have gained a powerful influence on the planet. 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 two other eon boundaries in Earth's history.
Yet to become a new eon, such a transition would require an additional quality: great longevity. Can this new force possibly persist for millions or billions of years? This is closely related to the subject of SETI (the Search for Extraterrestrial Intelligence), whose theorists have long recognized that the number of technological civilizations in the universe must be proportional to their average longevity. The literature of this field is filled with discussion of the potential longevity of human-like civilizations elsewhere in the galaxy. What exactly do we mean by "human-like?" That is a wonderful question that connects questions of our essential nature, our exceptionalism compared to the rest of life, and our role on the planet. Can a civilization become integrated into the cyclic functioning of its planet in a sustainable way? This implies a different mode of interaction with the planet than is currently being exhibited by "intelligent" life.
From a systems perspective, the early stages of this transition are highly unstable because global influence precedes global control. Such a system is characterized by unstable positive feedbacks which threaten catastrophe. Hence the dangers of our current "Anthropocene dilemma": We have global influence without global self-control. However, global technological influence clearly contains both peril and promise. Conscious awareness and control can also be sources of stabilizing negative feedback. This merely requires recognizing a problem and acting to fix it.
We've done this with our, so far, successful efforts to repair the ozone layer. There are pathways by which this stabilizing cognitive phenomenon could become a very long-lived and even permanent part of the Earth system. This would require that we reach a stage where we have a deep understanding of nature and an ability to forestall natural disasters, as well as the deep self-understanding necessary to forestall self-imposed disasters. In other words, it will require both technical and spiritual progress.
How does this affect the way we view our future? It reframes our task. And it puts our immediate challenges over the next century, stabilizing population and devising an energy system that can provide for the needs of this population without wrecking the natural systems upon which we depend, against the backdrop of a much longer-term challenge. Once we get over the relatively short-term, century-scale threat of destabilizing fossil-fuel induced climate change, we need to learn how to become a long-term stabilizing factor on the planet. This will include: over the next several hundred to thousand years, asteroid and comet defense; over the next several tens of thousands of years, learning how to prevent ice ages and natural episodes of dangerous global warming; over several billions of years, compensating for the warming sun and preventing the inevitable runaway global warming that will otherwise result from solar evolution.
Our current struggles and anxieties about the future must be faced with an awareness of the very long view. We need to have a vision of the world we want to create so that we can see ourselves as collaborators with future generations in the project of shaping it.
The story of our species is one of overcoming existential risk through new forms of cooperation and innovation. Our current dilemmas require these same skills applied on new temporal and spatial scales. Although right now we are initiating a mass extinction, in the long run, by preventing future extinctions and prolonging the life of the biosphere, we could be the best thing that ever happened to planet Earth.
David Grinspoon is a senior scientist at the Planetary Science Institute. His latest book, Earth in Human Hands: Shaping Our Planet's Future, was published in December 2016.