We like to think that we are an exception: An intelligent life that has developed a vastly complex industrialized civilization unlike anything seen before. But would we actually know if millions of years ago some other life forms had created huge cities, altered the landscape, and formed their own civilization? What would be left of their exploits for us to find?
This is the thought experiment that the director of NASA’s Goddard Institute for Space Studies, Gavin Schmidt, and professor of physics and astronomy at the University of Rochester, Adam Frank, have been exploring. They want to understand if any evidence of a hugely advanced civilization could persist tens of millions of years into the future and, if so, what form it might take. Their results are published in the International Journal of Astrobiology.
“Gavin and I have not seen any evidence of another industrial civilization,” Frank lays out from the onset. Since they have not found any pre-human civilization, they have been looking at what impact we as a species are having on the planet, and how long those impacts are likely to be detectable into the future. “These questions make us think about the future and the past in a much different way, including how any planetary-scale civilization might rise and fall.”
While we have plenty of evidence of past civilizations in the form of statutes and foundations that date back maybe a few thousand years at most, things get far more opaque when the clock is rolled back by a few million or hundreds of millions of years.
Calling this the “Silurian hypothesis” – after the technologically advanced reptiles from Dr. Who – they speculate what would be left if a civilization lasted for 100,000 years or so around 60 million years ago. That may sound like a long time, but in the history of the Earth, it is but a blip. However, the chance of fossils would be rare, so what else could we look for?
As a species, we are currently laying down all sorts of traces that will be detectable in a 100 million years’ time. In feeding 7 billion people, we’ve completely altered the nitrogen cycle, with much of it now finding its way into sediment at the bottom of the ocean and the tops of mountains. On the flip side, rare earth elements that were once buried deep are now floating free at the surface as we develop ever more complex technology.
That’s not to mention the changes in the carbon cycle from burning so much fossil fuel or the millions of tonnes of plastic being laid down. Some have even suggested that all the plastic we’re producing is forming a new kind of rock, and all these changes will still be detectable far into the future.
All this is obviously hypothetical at the moment, but it has an important point. These are the kind of clues we could use to look for previously advanced civilizations on other planets.
“We know early Mars and, perhaps, early Venus were more habitable than they are now, and conceivably we will one day drill through the geological sediments there, too,” says Gavin Schmidt. “This helps us think about what we should be looking for.”