We humans have always been fascinated by the past.
We have discovered countless fossils from the ground, relics from 4.5 billion years of Earth’s history, which give us clues about how ancient species lived long before our existence.
But if we ourselves disappeared and another intelligent species emerged millions of years from now, would they know we existed? Or what our civilization was like?
Small chance of becoming a fossil
We can’t count on future paleontologists finding our fossils, says Adam Frank, professor of astrophysics at the University of Rochester, US.
“Only a small fraction of life on Earth has fossilized, especially if your civilization lasted only a brief geological period,” he explains.
A 2018 paper, co-authored by Frank, points out that despite all the dinosaurs that roamed the Earth for 165 million years, few near-complete fossils have been discovered to date.
So the article suggests that given that our human species has only been around for about 300,000 years (so far), we may not have left much of a trace in the fossil record.
But we can leave different traces.
Changing Earth’s Chemistry
As part of the natural geology of the planet, rocks are continually deposited into the ground in layers or strata.
The chemical composition of each stratum is linked to the conditions of the planet at that time.
According to Frank, rising temperatures and sea level changes due to human-caused climate change will affect what is deposited in rocks, something that will be detectable “probably hundreds of millions of years from now.”
“We would see that there was a difference between oxygen isotopes and carbon isotopes due to the fact that the Earth’s climate system has changed due to human activity,” explains the astrophysicist.
Reshaping Evolution
Even though our own bones don’t show up much in the fossil record, it’s quite possible that we’ve modified the fossils of other species through the plants and animals we carry around the world or the biodiversity we modify.
A 2018 study found that 96% of all mammals in the world were us or our livestock, measured by biomass – the total weight of all living matter.
More than two thirds of the world’s avian biomass came from our domestic birds.
We slaughter more than 75 billion chickens each year, according to the nonprofit publication Our World in Data.
Therefore, the fossils of all these almost identical birds, dying in large numbers, may well raise eyebrows in the future.
“We have changed the course of biological evolution,” says Jan Zalasiewicz, a geologist, paleontologist and professor emeritus at the University of Leicester in the United Kingdom.
“Our explorers in the distant future will ask themselves: ‘What happened? Why did it happen?'” he suggests. “And they’re going to focus on the layer where it all started, and that’s our layer.”
Our “ultimate legacy”
In his book titled “Discarded: How Technofossils Will Be Our Ultimate Legacy” (Discarded: How Technofossils Will Be Our Final Legacy), Zelasiewicz and his colleague at the University of Leicester, Sarah Gabbott, say it will be our everyday objects that endure in Earth’s geological record.
They call these objects technofossils – whether it’s an aluminum drink can, a polyester sweater or an underground parking lot.
A 2020 study estimates that we produce 30 gigatons of objects per year. This is equivalent to each person on Earth producing more than their own body weight per week.
In fact, the authors discovered that we now have more man-made objects than living things when comparing their dry weight.
The largest proportion of human products comes from concrete, which may not seem very natural to future discoverers.
“One of the ways we produce concrete these days is by adding fly ash…under a microscope, (this stuff) looks absolutely weird,” Zelasiewicz says.
“If the edges of concrete buildings and paving slabs turn into fossilized shapes, (future archaeologists) will see that this is something very different from a natural stratum.”
Many of our materials will last a long time.
Plastic “could probably last not just thousands of years, but potentially millions of years,” says Gabbott.
We produce so much of the material that by 2050 there could be more plastic than fish in the ocean, according to the United Nations. But it’s not just plastic.
“We have rocks that are four billion years old that contain graphite,” Gabbott continues.
“So graphite in pencil form could last four billion years.”
The paleontologist says fossilized leaves dating back hundreds of millions of years ago have been found.
“Paper is made from cellulose, which is the same substance as leaves. And so… paper, in the right environment, could probably last hundreds of millions of years,” she speculates.
Changes on a global scale
It is quite possible that humans have already left a huge mark on Earth’s geology. It remains to be seen whether another intelligent species will ever see it, long after we are gone.
But is it useful to imagine our legacy millions of years into the future?
Professor Frank thinks so.
“I think it is vital for us to get through this period of technological immaturity, to be able to think about the long-term history of the Earth,” he argues.
“These are changes on a planetary scale that will have consequences over centuries, millennia, tens of millennia,” he says.
Based on a podcast episode Crowd science (in English), from the BBC World Service. With reporting by Ellen Tsang.
This text was originally published here.
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