Over the past 540 million years, Earth has suffered only five mass extinctions. In ultra-simplistic terms, that’s one every 108 million years, though it doesn’t really pan out like that. Past mass extinctions have been the result of catastrophic environmental calamities (a large number of them linked to CO2 emissions and climate change).
Scientists from the University of California, Berkeley warn that we are on the brink of pushing the planet into its sixth mass extinction if something isn’t done soon.
Published in the March 3 edition of the journal Nature, paleobiologists from UC Berkeley assessed where mammals and other species currently stand in terms of possible extinction, and compared that with the past mass extinctions.
Moving into the Mass Extinction Realm
“If you look only at the critically endangered mammals – those where the risk of extinction is at least 50 percent within three of their generations – and assume that their time will run out, and they will be extinct in 1,000 years, that puts us clearly outside any range of normal, and tells us that we are moving into the mass extinction realm,” said principal author Anthony D. Barnosky, UC Berkeley professor of integrative biology, a curator in the Museum of Paleontology and a research paleontologist in the Museum of Vertebrate Zoology.
“If currently threatened species – those officially classed as critically endangered, endangered and vulnerable – actually went extinct, and that rate of extinction continued, the sixth mass extinction could arrive within as little as 3 to 22 centuries.”
Not Too Late to Save Critically Endangered Species
Barnosky added, though, that it isn’t too late to save these critically endangered mammals and other species, and bring us up short of a tipping point which would lead to the planet’s sixth mass extinction.
“So far, only 1 to 2 percent of all species have gone extinct in the groups we can look at clearly, so by those numbers, it looks like we are not far down the road to extinction. We still have a lot of Earth’s biota to save,” Barnosky said. “It’s very important to devote resources and legislation toward species conservation if we don’t want to be the species whose activity caused a mass extinction.”
“Just because the magnitude [of documented extinctions] is low compared to the biggest mass extinctions we’ve seen in a half a billion years doesn’t mean to say that they aren’t significant,” said co-author Charles Marshall, UC Berkeley professor of integrative biology and director of the campus’s Museum of Paleontology. “Even though the magnitude is fairly low, present rates are higher than during most past mass extinctions.”
Comparing Past Extinctions to Current Extinctions Difficult
Barnosky organised a graduate seminar in 2009 bringing biologists and palaeontologists together in an attempt to compare the current extinctions with the extinctions seen in the fossil record, but as Barnosky notes, that’s “like comparing apples and oranges.”
Straight away, examining a fossil record which dates back 3.5 billion years is difficult, especially when the historical record only dates back a few thousand years. Worse is when you realise that the fossil record has many holes in it, making it impossible to include every species that evolved and then died out, which probably amounts to 99% of all species that have ever existed.
“If we find a mass extinction, we have great difficulty determining whether it was a bad weekend or it occurred over a decade or 10,000 years,” he said. “But without the fossil record, we really have no scale to measure the significance of the impact we are having.”
Nonetheless, Current/Potential Mass Extinction Seems Undeniable
To get around this limitation, Marshall said, “This paper, instead of calculating a single death rate, estimates the range of plausible rates for the mass extinctions from the fossil record and then compares these rates to where we are now.”
Barnosky’s team started with mammals because they are so well documented today as well as in the fossil record. They estimated that the average extinction rate for mammals is less than two extinctions every one million years.
However biologists estimate that within the past 500 years we have lost 80 mammal species out of a starting number of 5,570.
“It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining ‘mass extinction,’” Barnosky said.
After looking at the list of threatened species maintained by the International Union for Conservation of Nature (IUCN), the team concluded that if all mammals now listed as “critically endangered,” “endangered” and “threatened” go extinct, whether that takes several hundred years or 1,000 years, Earth will be in a true mass extinction.
“Obviously there are caveats,” Barnosky said. “What we know is based on observations from just a very few twigs plucked from the enormous number of branches that make up the tree of life.”
Scientists Urge that We Act Now to Prevent 6th Mass Extinction
He urges similar studies of groups other than mammals in order to confirm the findings, as well as action to combat the loss of animal and plant species.
“Our findings highlight how essential it is to save critically endangered, endangered and vulnerable species,” Barnosky added. “With them, Earth’s biodiversity remains in pretty good shape compared to the long-term biodiversity baseline. If most of them die, even if their disappearance is stretched out over the next 1,000 years, the sixth mass extinction will have arrived.”