Quirks & Quarks

Fossils of our civilization — what humans will leave behind

A thought experiment provides information about how to detect long-gone intelligent life
Would hieroglyphs like this be the sort of thing future archaeologists will find when excavating the remains of our civilization? Probably not, suggests Gavin Schmidt, as time will destroy even this kind of artifact. (CBC)

The hunt for ancient intelligent civilizations

Could an intelligent, industrial civilization have lived on Earth before humans?

That's a scenario that Gavin Schmidt, a climate scientist and director at the NASA Goddard Institute for Space Studies in New York, explored with astrophysicist Adam Frank in their recent paper titled, "The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record."

The answer is almost certainly no, according to Schmidt, but that's not why he asked the question.

"Our point here was not to say that any of these things happened," he says, "but that if you consider this as a possibility, there are things that you could look for that would be informative."

The Negev desert is the oldest geologically unaltered surface on the planet, about 1.5 million years old. Most things in our modern technological society like artefacts and monuments, will be erased in a relatively short period by erosion, tectonics and other geological forces, says Gavin Schmidt. (AFP/Getty Images)

His research has practical applications in the field of astrobiology, in which scientists contemplate how to look for life elsewhere in the universe. Much of this work involves finding traces of currently existing life, but the universe has had a long history. Schmidt's research speculated on how we might find evidence of intelligent life that might have lived hundreds of millions or billions of years ago. That kind of evidence, according to Schmidt, might be found in a planet's geological record.   

What to look for

To illustrate what he means, he contemplated a thought experiment. "We said, 'Let's think about what we're doing right now that will mark the geological record for millions, if not billions of years.'"

He noted the natural biogeochemical cycles that have been perturbed by humans and pollutants created by our activities. According to Schmidt, a few hundred million years from now, future geologists will probably not find the ruins of the Trump tower or other artifacts of civilization. Instead, they'll find globally distributed chemical evidence of our energy use —  a huge bump in organic carbon deposits from our fossil fuel use, isotopic evidence of a sudden temperature change, and a sudden disruption in nitrogen levels from synthetic fertilizer use. All this will be marked into Earth's geology.

Future geologists will find chemical evidence of human's fossil fuel use marked in Earth's geology. (Getty Images)

They may also find evidence of changes in sedimentation from the way we changed land and water use, notice the increase in extinctions human activity has driven, and might find some strange non-natural, but persistent chemicals like organic pollutants, polychlorinated biphenyls (PCBs), and, of course, plenty of plastics. These are the sort of signs of an industrialized civilization that we should look for, says Schmidt, because they will be preserved through time.

What not to look for

Schmidt says what will not likely be preserved through time are most of the products of our modern technological society like buildings, and monuments, which will be erased in a relatively short period by erosion, tectonics, and other geological forces.

The oldest geologically unaltered surface on the planet is the Negev desert — which is about 1.8 million years old, says Schmidt.  Any surface older than that has been buried, inundated, or eroded away.

It's not even likely that our skeletons will survive as fossils. Animal fossils don't make that good a signature of past life. When we look at dinosaurs, he points out, we only have one sample for every 100,000 years of their existence — and that's an average — there are chunks of several million years with nothing.

now