Saturday, June 24, 2023

Could An Industrial Civilization Have Existed On Earth Before Our Own?

SA  |  One of the creepier conclusions drawn by scientists studying the Anthropocene—the proposed epoch of Earth’s geologic history in which humankind’s activities dominate the globe—is how closely today’s industrially induced climate change resembles conditions seen in past periods of rapid temperature rise.

“These ‘hyperthermals,’ the thermal-maximum events of prehistory, are the genesis of this research,” says Gavin Schmidt, climate modeler and director of the NASA Goddard Institute for Space Studies. “Whether the warming was caused by humans or by natural forces, the fingerprints—the chemical signals and tracers that give evidence of what happened then—look very similar.”

The canonical example of a hyperthermal is the Paleocene-Eocene Thermal Maximum (PETM), a 200,000-year period that occurred some 55.5 million years ago when global average temperatures rose by five to eight degrees Celsius (nine to 14 degrees Fahrenheit). Schmidt has pondered the PETM for his entire career, and it was on his mind one day in 2017 when University of Rochester astrophysicist Adam Frank paid him a visit.

Frank came to his office to discuss the idea of studying global warming from an “astrobiological perspective”—that is, investigating whether the rise of an alien industrial civilization on an exoplanet might necessarily trigger climate changes similar to those we see during Earth’s own Anthropocene. But almost before Frank could describe how one might search for the climatic effects of industrial “exocivilizations” on newly discovered planets, Schmidt caught him up short with a surprising question: “How do you know we’re the only time there’s been a civilization on our own planet?“

Frank considered a moment before responding with a question of his own: “Could we even tell if there had been an industrial civilization [long before this one]?“

Their subsequent attempt to address both questions yielded a provocative paper on the possibility that Earth might have spawned more than one technological society during its 4.5-billion-year history. And if indeed some such culture arose on Earth in the murky depths of geologic time, how might scientists today discern signs of that incredible development? Or, as they put it in the paper: “If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today?“

Schmidt and Frank began by forecasting the geologic fingerprints the Anthropocene is likely to leave behind—such as hints of soaring temperatures and rising seas laid down in beds of sedimentary rock. These features, they noted, are very similar to the geologic leftovers of the PETM and other hyperthermal events. They then considered what tests could plausibly distinguish an industrial cause from otherwise naturally occurring climate changes. “These issues have never really been addressed to any great extent,” Schmidt notes. And that goes not only for scientists but evidently for science-fiction writers as well, he adds: “I looked back into the science-fiction literature to try to find the earliest example of a story featuring a nonhuman industrial civilization on Earth. The earliest I could find was in a Doctor Who episode.“

That 1970 episode of the classic TV series involves the present-day discovery of “Silurians”—an ancient race of technologically advanced, reptilian humanoids who predated the arrival of humans by hundreds of millions of years. According to the plot, these highly civilized saurians flourished for centuries until Earth’s atmosphere entered a period of cataclysmic upheaval that forced Homo reptilia to go into hibernation underground to wait out the danger. Schmidt and Frank paid tribute to the episode in the title of their paper: “The Silurian Hypothesis.”

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