Fossils show oblivion’s malign impact on nature

Lake Volvi in Greece periodically dries up because of excessive irrigation coupled with climate change −  one freshwater system under human impact. Image: By courtesy of C. Albrecht (JLU)

We are obliterating other life: oblivion’s malign impact could bring extinction faster than at almost any time known so far.

LONDON, 28 May, 2021 − Evolutionary biologists have looked at the timetable of mass murder 66 million years ago in what is now called the Fifth Great Extinction. By looking at fossil snails and other freshwater citizens of what is now Europe, they traced oblivion’s malign impact over many millennia.

The grim news is that the loss of species began soon after a substantial comet or asteroid crashed into planet Earth, but it took another 12 million years for evolution to catch up again.

The even grimmer news is that the Sixth Great Extinction has already begun, and is proceeding at a rate 1,000 times faster than the massacre of the little creatures that perished alongside the dinosaurs.

The message − familiar for decades to conservationists, evolutionary biologists and palaeontologists, but still to be appreciated by politicians − is that the impact of more than 7 billion humans on the rest of the living world is less immediate, but more devastating, than the celestial traffic accident that wiped out the dinosaurs.

“We have assured that the effects of our actions will outlast us by millions of years”

And it looks set to continue. A century from today, a third of freshwater species living now may have vanished from the face of the planet. And it won’t stop there.

“Even if our impact on the world’s biota stops today, the extinction rate will likely stay high for an extended period of time,” said Thomas Neubauer, of Justus Liebig University Giessen in Germany.

“Considering that the current biodiversity crisis advances much faster than the mass extinction event 66 million years ago, the recovery period may be even longer. Despite our short existence on Earth, we have assured that the effects of our actions will outlast us by millions of years.”

Dr Neubauer and his colleagues report in the journal Nature Communications Earth and Environment that they considered the fossils of 3,122 species of European freshwater gastropods unearthed in 24,759 instances, to calculate extinction rates over the last 200 million years.

They selected the snails because snails’ shells are distinctive, and preserved; and because freshwater ecosystems occupy only about 1% of the planet’s surface, but are home to perhaps 10% of all species.

Lessons from Europe

And they settled on European evidence because Europe has, they write, an “exceptionally rich and well-studied fossil record”. European biologists, too, have a more complete record of living species for comparison.

More importantly, they had enough data to work out the rates at which old species become extinct and new species evolve on a stable planet under normal conditions over hundreds of millions of years. From that, they could confirm that after the devastating impact that brought the Cretaceous era to a close − and wiped out the dinosaurs − conditions on Earth were harsh enough to force a greater rate of extinction for the next 5.4 million years.

In that time, 92.5% of all species were extinguished: the rate of extinction increased by an order of magnitude − that is, around tenfold. Although new species emerged, it was another 6.9 million years before recovery was complete.

“However, present extinction rates in European freshwater gastropods are three orders of magnitude higher than even these revised estimates for the Cretaceous-Palaeogene mass extinction,” the researchers write. That is, present extinction rates are already 1,000 times faster than one unpredictable moment of global devastation 66 million years ago. It follows that extinction rates must be four orders of magnitude − 10,000 times − faster than in a period of evolutionary stability.

Snails matter too

That life’s evolution has been marked by periodic extinction has been firmly settled for more than a century, and an overload of greenhouse gases in the atmosphere has been an agent of at least one of them, and perhaps an actor in all.

What alarms today’s biologists is that they can see it all happening again, as human numbers grow and human economies alter the planetary atmosphere. And they have said so, repeatedly.

In this study, they spell it out it again. “The current biodiversity crisis appears even more drastic, with species being lost at a much faster pace. Our analyses suggest that 75% of all European species may be lost within centuries. Our findings provide yet additional evidence that immediate and effective action is needed to protect biodiversity,” they write.

Just in case anybody thinks freshwater snails don’t matter to humans, they do. They are part of a functioning ecosystem on which terrestrial life depends.

“Losing species entails changes in species communities and, in the long run, this affects ecosystems,” said Dr Neubauer.“We rely on functioning freshwater environments to sustain human health, nutrition and freshwater supply.” − Climate News Network