In the past 540 million years, the Earth has endured five mass extinction events, each involving processes that upended the normal cycling of carbon through the atmosphere and oceans. These globally fatal perturbations in carbon each unfolded over thousands to millions of years, and are coincident with the widespread extermination of marine species around the world.
In January of 2018, The Galaxy posted “Point of No Return” –MIT Scientist Predicts the Event Horizon for Earth’s 6th Mass Extinction. The question for many scientists is whether the carbon cycle is now experiencing a significant jolt that could tip the planet toward a sixth mass extinction. In the modern era, carbon dioxide emissions have risen steadily since the 19th century, but deciphering whether this recent spike in carbon could lead to mass extinction has been challenging. That’s mainly because it’s difficult to relate ancient carbon anomalies, occurring over thousands to millions of years, to today’s disruptions, which have taken place over just a little more than a century.
“How can you really compare these great events in the geologic past, which occur over such vast timescales, to what’s going on today, which is centuries at the longest?” says Daniel Rothman professor of geophysics and co-director of MIT’s Lorenz Center.
“This is not saying that disaster occurs the next day,” says Rothman about his MIT study. “It’s saying that, if left unchecked, the carbon cycle would move into a realm which would be no longer stable, and would behave in a way that would be difficult to predict. In the geologic past, this type of behavior is associated with mass extinction.”
In an interview with Kevin Berger, editor of Nautil.us, British biologist Chris Thomas observes that a loss of around 10 percent of species “falls far below the level of extinction (75 percent plus) required to match one of the previous ‘Big Five’ mass extinctions in the geological past.”
Humans are just another animal on the planet, says Thomas: “Our actions are not outside the engine of evolution, even though we have the most horsepower. Environmentalists need to stop fencing off nature from humans, he argues, understand the mechanics of evolution better, including our role in it. The Sixth Great Extinction, he tells us, is premature.”
Extinction is only one side of evolution. Earth’s system is simply what it is, writes Thomas: “It now contains the human species as well as other species. That is the system we have, but we cannot distinguish between the human parts from the inhuman parts. Humans evolve within the system, so we are part of the system. Unless you go deep into rocks or some such location, you cannot identify locations where the impacts of humans are zero.”
“Virtually all countries and islands in the world have experienced substantial increases in the numbers of species that can be found in and on them,” writes Thomas in Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction.
Thomas is a professor of conservation biology at the University of York in England. He is not easily pigeonholed. He has been a go-to scientist for the media and lawmakers on how climate change is scorching the life out of animals and plants. At the same time he can turn around and write, “Wild geese, swans, storks, herons and cranes are returning as well, and the great whales, the largest animals ever to have lived on Earth, are once more plying their way across our seaways in numbers after centuries of unsustainable butchery.”
“I’m concerned a lot of resources being spent on conservation are focused on trying to keep things exactly as they are, or revert to some imagined past,” says Thomas. “As great as those aspirations might be, in the long run, they’re doomed.”
“There has been a huge acceleration of the extinction rate in the human epoch, Thomas observes, and that if we keep up the current rate of extinction for the next 10,000 years, we end up with a mass extinction of 75 percent of species going extinct. That is equivalent to the percentage that went extinct when the dinosaurs died out. And 10,000 years or even 100,000 years is an extraordinarily short period in geological history.
But could it be that we’re spurring evolution too fast? asked Berger. Maybe the rate at which the change is going on now, compared to the past, is too fast for there to be corrections.
“Evolution is a process,” says Thomas, “It can’t be too fast or too slow. It just happens. Under some circumstances it’s faster and slower. By and large, the faster the environment changes, the faster evolution takes place, because some lineages are lost and some are able to diversify under the new conditions. Yes, there could be a rate of change that was so fast that evolutionary adaptations were incapable of keeping up with it. But there isn’t any evidence at the moment that we are beyond some kind of tipping point beyond which evolution can’t hack it any longer. Look at how fast things evolve resistance to pesticides, or how many species manage to colonize new parts of the world that we have disturbed.
Thomas calls the current epoch Earth Anthropocene Park: “To focus our thinking on the fact that we are both the inmates of the park and its managers. And to take issue with the dream of unaffected nature. A park is a modified environment and so calling our world Anthropocene Park gets us away from thinking there are any places unaffected by us. Every decision we make, or every time we decide not to intervene, has an influence on the biodiversity of a particular place and on the planet as a whole. Like it or not, we are managing the world species and ecosystems. We have to get used to that. We are part of the system.”
Humans have changed the world a lot, and some of the changes do look like destruction, Thomas adds. “But destruction is a bit of a subjective word. Normally we change one type of habitat into another. You’ve just got to get real that every biological system is modified by us.”
We’re the species with the big brain, Berger says. We have the technology and ability to shape the natural world to our own ends. Do you think we have an ethical responsibility to conserve nature, he asks Thomas.
“The difficulty is time goes forward. The biological processes of the birth and death of individuals, the better survival of some species than others, the evolution of new genetic types—all of the biological processes that take place on the planet—are dynamic ones. The expectation that things should stay exactly as they are is not a realistic expectation of the biological systems of the world.”