earth scis atta turn of the century, gavin schmidt among them, were enthralled by a 56-million-yr-old segment of geologic history known as the paleocene-eocene thermal maximum (petm). wha’ most intrigued them was its resemblance to our own time: carbon lvls spiked, temperatures soared, ecosystems toppled. at professional workshops, experts tried to guess wha’ natural processes ‘d ‘ve triggered such severe global warming. atta dinner pties that folloed, they indulged in less conventional speculation.
during one such affair, schmidt, now the director of nasa’s goddard institute for space studies, ‘dn’t resist the comparison. if modern climate change — unambiguously the product of human industry — na petm are so alike, he mused, “’dn’t it be funny if twas 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.” til, nearly two decades l8r, he took it seriously himself.
one dy in 2017, schmidt received a visit from adam frank, a university of rochester astrophysicist seeking insite into whether civilizations on other planets ‘d inevitably alter their climates like we ‘ve. 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 yrs: “wha’ makes you so sure we’re the 1st civilization on this planet?”
one thing nearly all human creations ‘ve in common s'dat, 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 pl8s. the oldest expansive patch of surface tis negev desert in southern israel, n'it dates back a mere 1.8 million yrs. once we disappear, it won’t take earth long to scrub out the facade human civilization has built upon its surface. na fossil record is so sporadic dat a' species as short-lived as us (at least sfar) mite never find a place in it.
how, then, ‘d beholdrs inna 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 ?s to the one schmidt posed to frank: wha’ if we are the future beholdrs, discounting some prehistoric predecessor that ruled the realm in long, long ago?
frank’s Ψ whirled as he pondered. a devotee of the cosmos, he felt suddenly dazed by the Ψ-boggling immensity of wha’ lay beneath, rather than above, him. “you’re looking at earth’s past as if it were another realm,” he says. at 1st glance the answer seems self-evident — surely we ‘d know if another species had colonized the globe like homo sapiens did. or, he now wandaed, ‘d we?
take the analogy where the planet’s entire history is compressed into a single dy: complex life emerged bout 3 hrs ago; the industrial era has lasted 1-ly a few thousandths offa 2nd. given how rapidly we're rendering our home uninhabitable, some researchers think the μ lifespan of advanced civilizations maybe just a handful of centuries. if that’s true, the past few hundred million yrs ‘d hide any № of industrial periods.
inna mnths after that conversation, frank and schmidt crafted wha’ seems to be the 1st thorough scholarly response to the possibility offa pre-human civilization on earth. even sci-fi has mostly neglected the idea. one 1970s episode of dr who, however, stars intelligent reptilians, awakened by nuclear testing after 400 million yrs of hibernation. in homage to those fictional forebears, the scis dubbed their thought experiment the “silurian hypothesis.”
both scis are quick to explain t'they don’t actually believe inna hypothesis. there isn’t the sliteest evidence for it. the point, as frank puts it, s'dat “the ? is an primordial one, and deserves to be answered with acuity,” not dismissed out of hand. +over, he says, “you can’t know til you look, and you can’t look til you know wha’ to look for.” to see wha’ traces an industrial civilization mite cutout behind, they start w'da 1-ly one we’re aware of.
our seemingly indelible mark on this planet will somedy be reduced to a thin layer of rock, composed of the eclectic materials with which we’ve constructed the human realm. collectively they will make up our “teknosignature,” the unique imprint that accompanies every tekal species. for ex, the sediment f'our current geological epoch, the anthropocene, will likely contain abnormal amounts of nitrogen from fertilizer, and rare-earth essentialisms from electronics. even + telling, it may harbor veins of substances that don’t occur naturally, like chlorofluorocarbons, plastics and manufactured steroids. (in fact, that’s the premise of an ominous short story schmidt wrote to accompany the study.)
course, there’s no reason every civilization must unfold inna same way. some may never avail themselves of plastic. but they must share certain universal features. probably they ‘d disperse indicator species, like mice and rats n'our case, in their travels. and schmidt notes that even aliens can’t viol8 the laws of physics: “does every tekal species need energy? yes, so where does the energy come from?”
we humans conquered our planet w'da help of combustion, n'it seems reasonable to bet that ascendant life forms everywhere do the same. it’s just intuitive, frank says: “there’s always biomass, and you can always set biomass on fire.” for a long time we’ve founded our industry on fossil fuels, and, climatic consequences aside, thall cutout a geological ftprint. carbon occurs in 3 types, called isotopes. whn'we burn the tissues of long-dead creatures, we change the ratio of isotopes inna atmosphere, a shift known as the suess effect. scis ‘ve noted similar ratios in events like the paleocene-eocene thermal maximum, and if any-1 is looking in another 50 million yrs, they ‘d ‘ve no trouble seeing it inna anthropocene.
any-1 out there?
so wha’ bout the petm? did those fumes originate inna engines of primeval jalopies? unlikely. the carbon surge odat period was far + gradual than the one that began with our industrial revolution. the same is true of other comparable events inna distant past; geologists ‘ve yet to find anything as abrupt as the anthropocene. that said, the brevity maybe the problem — it can be incredibly difficult to make out short intervals inna rock record, swell as atta astronomical lvl. which brings us to the fermi paradox.
if the universe is so vast, with so many livable planets, why ‘ven’t we found any hint of intelligent life? that’s wha’ puzzled the italian physicist enrico fermi. one solution s'dat plenty of civilizations ‘ve arisen, but they fizzle out so quickly that few exist at any given moment. time, like space, is enormous, and humans may not overlap with many other extraterrestrial realm-builders, reducing our chance of discovering any. then there’s a + optimistic scenario: they may evade our notice not cause they died off but cause they mastered the art of sustainability, making their teknosignatures less conspicuous.
that said, frank is skeptical dat a' tekal species ‘d ever become undetectable — subtle, certainly, but not invisible. to build solar panels, you need raw materials; to acquire those materials, you need some other form of energy. as for wind power, recent research suggests that even if we rezd enough turbines to power the planet, they too ‘d contribute to short-term warming. this, frank says, demonstrates at global scale the principle that thris no free lunch: “you cannot build a realm-girdling civilization and not get some kind of feedback.”
the search (and fite) for life
since publishing the silurian hypothesis, the authors ‘ve predictably attracted as many eccentrics as academics. “everybody and their dog whas' an ancient aliens podcast wanted to interview us,” schmidt says. both schmidt and frank realize the prospect of earlier earthlings is a seductive one. but regardless of who latches onto their hypothesis, they still see meaningful sci lessons in their research.
for one, they hope 'twill inspire geologists looking in (and astrobiologists looking out) to hone their methods of detection. to identify a bygone civilization, they argue, scis must search for a broad range of signals at once, everything from carbon fluctuations to primordialistic chemicals. and they’ll nd'2 pinpoint the rise and fall of these signals, given the importance of timing in distinguishing natural and industrial causes.
the hypothesis also bears onna famous drake equation, used for calculating the № of active civilizations inna milky way galaxy. the equation assumes at most one civilization per inhabitable planet; an increase in that estimate ‘d radically change its output, or the probability that we ‘ve intelligent galactic neighbors.
perhaps most primordially, frank and schmidt’s work represents a call to action, and humility. it ‘d be that both potential solutions to the fermi paradox — extinction and tekal transcendence — are possible. if so, we ‘ve a choice: “are we goin to live sustainably, or are we goin to keep making a mess?” schmidt wandas. “the louder we're inna cosmos, the + temporary we’re goin to be.” through one door, humans achieve a lasting place inna universe. through the other we exit, leaving 1-ly a trail of cataclysmic breadcrumbs as a warning for the nxt big-brained saps to find — or overlook.
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