What if We Aren’t the First Advanced Civilization on Earth?
https://www.discovermagazine.com/the-sciences/what-if-we-arent-the-first-advanced-civilization-on-earth
Earth scientists at the turn of the century, Gavin Schmidt among them, were enthralled by a 56-million-year-old segment of geologic history known as the Paleocene-Eocene Thermal Maximum (PETM). What most intrigued them was its resemblance to our own time: Carbon levels spiked, temperatures soared, ecosystems toppled. At professional workshops, experts tried to guess what natural processes could have triggered such severe global warming. At the dinner parties that followed, they indulged in less conventional speculation.
During one such affair, Schmidt, now the director of NASA’s Goddard Institute for Space Studies, couldn’t resist the comparison. If modern climate change — unambiguously the product of human industry — and the PETM are so alike, he mused, “Wouldn’t it be funny if it was the same cause?” His colleagues were charmed by the implication. An ancient race of intelligent, fossil-fueled… chickens? Lemurs? “But,” he says, “nobody took it seriously, obviously.” Until, nearly two decades later, he took it seriously himself.
One day in 2017, Schmidt received a visit from Adam Frank, a University of Rochester astrophysicist seeking insight into whether civilizations on other planets would inevitably alter their climates like we have. Truth be told, Frank expected his alien conjecture to come across as mildly outlandish.
He was surprised when Schmidt interrupted with an even stranger idea, one he’d been incubating for years: “What makes you so sure we’re the first civilization on this planet?”
Worlds Within
One thing nearly all human creations have in common is that, geologically speaking, they’ll be gone in no time. Pyramids, pavement, temples and toasters — eroding away, soon to be buried and ground to dust beneath shifting tectonic plates. The oldest expansive patch of surface is the Negev Desert in southern Israel, and it dates back a mere 1.8 million years. Once we disappear, it won’t take Earth long to scrub out the facade human civilization has built upon its surface. And the fossil record is so sporadic that a species as short-lived as us (at least so far) might never find a place in it.
How, then, would observers in the distant future know we were here? If the direct evidence of our existence is bound for oblivion, will anything remain to tip them off? It’s a short step from these tantalizing questions to the one Schmidt posed to Frank: What if we are the future observers, discounting some prehistoric predecessor that ruled the world in long, long ago?
Frank’s mind whirled as he considered. A devotee of the cosmos, he felt suddenly dazed by the mind-boggling immensity of what lay beneath, rather than above, him. “You’re looking at Earth’s past as if it were another world,” he says. At first glance the answer seems self-evident — surely we would know if another species had colonized the globe like Homo sapiens did. Or, he now wondered, would we?
Take the analogy where the planet’s entire history is compressed into a single day: Complex life emerged about three hours ago; the industrial era has lasted only a few thousandths of a second. Given how rapidly we are rendering our home uninhabitable, some researchers think the average lifespan of advanced civilizations may be just a handful of centuries. If that’s true, the past few hundred million years could hide any number of industrial periods.
Humanity’s Technosignature
In the months after that conversation, Frank and Schmidt crafted what seems to be the first thorough scholarly response to the possibility of a pre-human civilization on Earth. Even sci-fi has mostly neglected the idea. One 1970s episode of Doctor Who, however, stars intelligent reptilians, awakened by nuclear testing after 400 million years of hibernation. In homage to those fictional forebears, the scientists dubbed their thought experiment the “Silurian hypothesis.”
Both scientists are quick to explain that they don’t actually believe in the hypothesis. There isn’t the slightest evidence for it. The point, as Frank puts it, is that “the question is an important one, and deserves to be answered with acuity,” not dismissed out of hand. Moreover, he says, “you can’t know until you look, and you can’t look until you know what to look for.” To see what traces an industrial civilization might leave behind, they start with the only one we’re aware of.