People ask me what I study. I will say “astrobiology.” They’ll ask exactly what that involves. I’ll say that we’re trying to understand the nature of life and whether or not there’s other life in the universe. Almost a hundred percent of the time the very next question is what I think the answer is.
One the one hand it’s perfectly reasonable for me to be asked this. It’s like meeting someone who says they’re searching for a way to prevent aging. You are going to want to know what they think the odds of success are. But it’s also an unintentionally preposterous question—if any of us thought we knew these answers we’d already be finished, and unemployed.
Consequently, I’ve often answered the question about life in the universe by being as scientifically honest (and polite) as I know how to be. I’ll say that there are all sorts of things that would seem to support the possibility: The ubiquity of carbon chemistry in the universe. The enormous number of planetary systems that we now know exist across our galaxy. The likelihood of worlds that may have resembled the Earth in its youthful years, flush with chemical energy and promise.
But I’ll add to all of that (assuming I’ve not already lost the person’s interest) the fact that our solar system may be somewhat unusual in its configuration and contents. Or that, despite much scrutiny, we still have no real idea how life is initiated, or what is truly essential for its persistence on a planet.
In other words, like any good scientist, I would weasel out of a firm response.
But these days my answer is often much more specific. Yes, I say, there are probably other places in the cosmos with organisms like microbes, or their equivalent. But as important as that is or might seem, it is of little consequence compared to the question of whether or not there is other complex, thinking life with an elaborate sense of agency. Not because of what that would do to our most deeply held beliefs about the nature and uniqueness of humans, but because it would tell us what our chances are.
On the one hand, life on Earth looks like a single experiment, an outburst of a phenomenon that appears to have a continuous lineage reaching back some four billion years. But that way of seeing things also obscures the fact that “life” consists of untold numbers of nested, networked, interrelated experiments—like the most obscenely complex Matryoshka doll set. In many ways, each strand of DNA in each living cell on the planet today is its own unique microscopic laboratory test case.
And, as much as we’ve come to realize that humans are entirely contained within this multilayered history, it’s also clear that we’re a very particular, perhaps unprecedented, offshoot. Another experiment yes, but one that does not appear to have that many parallels with any of the others the planet has seen.
A couple of hundred thousand years ago there were not that many of our species. By the early 1700s, there were some six hundred million of us. Today there are over 7.7 billion. We pepper the Earth’s landscape in a curious way. Urbanized areas, which are projected to contain nearly 70% of humans in coming years, at present only cover about 1% of the land area of the planet. But our imprint on the world is ridiculously disproportionate.
Our presence is causing enough reduction in the diversity of species to suggest an extinction event. Our ingenious efforts to tap into energy resources far exceeding our base metabolic needs have pushed thousands of billions of tons of carbon dioxide into Earth’s atmosphere that otherwise wouldn’t have got there. What persists in the atmosphere, rather than being absorbed into sinks like the oceans and plant life, has caused a rise in global mean surface temperatures at a rate some twenty times faster than anything in the past two million years.
In other words, we represent an enormous and possibly unique perturbation to the world. A perturbation facing down an existential turning point of its own making. And this is precisely where the quest to understand life across the universe connects to life on Earth.
If there are other multi-billion-year experiments amongst the hundreds of billions of stars in our galaxy it is possible that some have led to circumstances like our own. That means that there could be places to learn from, to see whether technological species can moderate themselves, dodging self-induced implosion and constructing civilizations that face only the perils of a dynamic universe, not just their own tendencies.
If that sounds like a far-fetched target, well, yes in many respects it is. However, what we’re learning is that simply asking the question—gearing up to probe the solar system and the broader cosmos with telescopes, robots, simulations, and applying plain old scientific imagination—is itself providing vital clues.
Motivated by a wealth of exoplanetary discoveries we’re investigating how rocky planet environments may behave across not just deep time, but in alien configurations around small, weedy red stars, or in binary systems where twin suns sit in planetary skies. These studies are already revealing unexpected patterns in extreme climates, testing the fundamentals of our understanding of how any world functions, including perhaps our own.
Astronomers are also examining what life and technology might do to planetary atmospheres; from chemical signatures of organisms to industrial pollution that could be spied from across interstellar space. And researchers are building models of the root dynamics between a species’ energy demands and growth and how a planet responds to those demands. In other words, we’re constructing a scientific basis for analyzing how all of the galaxy’s life experiments play out, and what their options really are.
One of the reasons that these intellectual quests excite and inspire so many of us is not because we’re avoiding real issues, safe in our privileged towers, but because these quests exemplify our species’ better side. The side worth fighting for. The astonishing sense of agency and capacity for imaginative thought that has emerged on this tiny speck of cosmic matter. The unwillingness to give in to willful ignorance, and the drive to seek out equitable solutions for human existence. And in the end, our chances for persisting in a vast universe may hinge on our willingness to think big.
— Caleb Scharf is director of astrobiology at Columbia University