There have been five mass extinction events in the history of the Earth. In his book "The Ends of the World," author Peter Brannen looks at what happened to cause these crises — from massive volcanic eruptions to asteroids — and tries to determine what our future might bring.
Here & Now's Jeremy Hobson talks with Brannen (@PeterBrannen1) about how climate change and increasing levels of carbon dioxide could lead to another mass extinction, and what we can do to prevent it.
On how climate change relates to mass extinctions
"I think there's been, at least in the popular imagination, there's this understanding that mass extinctions are what happens when asteroids hit the planet, and I think there's been this really cool story over the past few decades from the paleontology and geology community where, they've looked for evidence of asteroid impacts at all the mass extinction levels, and except for the one we know about when the dinosaurs go extinct, all the mass extinctions seem to have a lot to do with these giant ocean and climate changes that are driven by carbon dioxide. So, in the first mass extinction a long time ago, it seems like there was an ice age from falling CO2, and then in some of the other mass extinctions, it seems like there's extreme global warming and ocean acidification, and some of the same stuff we see going on today, driven by carbon dioxide."
On what a mass extinction is
"The mass extinctions are really five times where over 75 percent of complex life goes extinct in what geologically is a really quick period of time, so tens of thousands of years at the most, and maybe much quicker than that."
On reef collapse as a warning sign of mass extinction
"So, that's definitely one of the more alarming things, is that there have really only been these things called 'reef collapses' a few times in the entire history of animal life, and, often times they're associated with these mass extinctions. There's this time, the end-Triassic mass extinction, where 75 percent of life went extinct, and coral reefs had this amazing sort of blossoming in the end of the Triassic. They make up a lot of the Austrian Alps, if you hike up those mountains you can kind of see they're just made of coral reefs. And at the end of the Triassic, coral reefs basically disappear completely for millions of years. Too much CO2, when it reacts with sea water, it makes the water more acidic, it makes it warmer, and it makes it really difficult for things like coral reefs to stick around. And so when we plot out what humans are doing for the next few decades, coral reefs are really gonna have a hard time sticking around in the second half of this century. Given that that's only happened a few times in Earth's history, that's really pretty amazing that humans have that influence."
"The mass extinctions are really five times where over 75 percent of complex life goes extinct in what geologically is a really quick period of time, so tens of thousands of years at the most, and maybe much quicker than that."Peter Brannen
On whether mass extinctions happen quickly, or take hundreds, thousands or millions of years
"I think this is kind of an urgent question to address, because it's hard to sort of see with high resolution in the fossil record things that happened hundreds of millions of years ago. So, maybe these are good analogs for the near future, or maybe these things really do take thousands of years. I think that's something we're trying to figure out. Some people will tell you that the dinosaurs were wiped out in 15 minutes in a really bad day, and other people would say that it was sort of this more prolonged thing, where ecosystems were stressed by a lot of things, and the asteroid, and these crazy volcanoes in India — it might have been a more prolonged episode that lasted thousands of years, so I think we need to get a better handle of how quickly these things can happen."
On whether humans have the capacity to fix the current problems
"Certainly we need to transform our energy system in the next decade or two. There's an incredible challenge that there's reason to be skeptical whether humans can do that, but there's other steps we can take. We know that if you just let life sort of have a chance to bounce back, it's incredibly resilient. A couple decades ago, you weren't supposed to eat swordfish, because we almost fished it to extinction, and now we've let swordfish rebound, and their stocks are healthy again, and there is a movement towards setting aside more of nature for protected areas, [former President] George W. Bush notably set aside the biggest marine protected area at the time. It shouldn't be a political issue, it hasn't always been a political issue, and I think it's a shame that environmentalism and stewardship of the planet has become one, and hopefully we can move away from that."
On if we can avoid another mass extinction
"I think we can, unless we just stick our head in the sand and do things the same way we've been doing it for the last 50 to 100 years, I think we can. In my better moods, I'm hopeful about humanity's ability to learn and adapt to the changing world around them."
Book Excerpt: 'The Ends Of The World'
By Peter Brannen
Animal life has been all but destroyed in sudden, planetwide exterminations five times in Earth’s history. These are the so-called Big Five mass extinctions, commonly defined as any event in which more than half of the earth’s species go extinct in fewer than a million years or so. We now know that many of these mass extinctions seem to have happened much more quickly. Thanks to fine-scale geochronology, we know that some of the most extreme die-offs in earth history lasted only a few thousand years, at the very most, and may have been much quicker. A more qualitative way to describe something like this is Armageddon.
The most famous member of this gloomy fraternity is the End-Cretaceous mass extinction, which notably took out the (nonbird) dinosaurs 66 million years ago. But the End-Cretaceous is only the most recent mass extinction in the history of life. The volcanic doomsday whose stony embers I saw exposed in the cliffs next to Manhattan— a disaster that brought down an alternate universe of distant crocodile relatives and global coral reef systems— struck 135 million years before the death of the dinosaurs. This disaster and the three other major mass extinctions that preceded it are invisible, for the most part, in the public imagination, long overshadowed by the downfall of T. rex. This isn’t entirely without reason. For one thing, dinosaurs are the most charismatic characters in the fossil record, celebrities of earth history that paleontologists who work on earlier, more neglected periods scoff at as preening oversized monsters. As such, dinosaurs hog most of the popular press spared for paleontology. In addition, the dinosaurs were wiped out in spectacular fashion, with their final moments punctuated by the impact of a 6-mile-long asteroid in Mexico.
But if it was a space rock that did in the dinosaurs, it seems to have been a unique disaster. Some astronomers outside the field push the idea that periodic asteroid strikes caused each of the planet’s other four mass extinctions, but this hypothesis has virtually no support in the fossil record. In the past three decades, geologists have scoured the fossil record looking for evidence of devastating asteroid impacts at those mass extinctions, and have come up empty. The most dependable and frequent administrators of global catastrophe, it turns out, are dramatic changes to the climate and the ocean, driven by the forces of geology itself. The three biggest mass extinctions in the past 300 million years are all associated with giant floods of lava on a continental scale— the sorts of eruptions that beggar the imagination. Life on earth is resilient, but not infinitely so: the same volcanoes that are capable of turning whole continents inside out can also produce climatic and oceanic chaos worthy of the apocalypse. In these rare eruptive cataclysms the atmosphere becomes supercharged with volcanic carbon dioxide, and during the worst mass extinction of all time, the planet was rendered a hellish, rotting sepulcher, with hot, acidifying oceans starved of oxygen.
But in other earlier mass extinctions, it might have been neither volcanoes nor asteroids at fault. Instead, some geologists say that plate tectonics, and perhaps even biology itself, conspired to suck up CO2 and poison the oceans. While continental-scale volcanism sends CO2 soaring, in these earlier, somewhat more mysterious extinctions, carbon dioxide might have instead plummeted, imprisoning the earth in an icy crypt. Rather than spectacular collisions with other heavenly bodies, it has been these internal shocks to the earth system that have most frequently knocked the planet off course. Much of the planet’s misfortune, it seems, is homegrown.
Luckily, these uber-catastrophes are comfortingly rare, having struck only five times in the more than half a billion years since complex life emerged (occurring, roughly, 445, 374, 252, 201, and 66 million years ago). But it’s a history that has frightening echoes in our own world— which is undergoing changes not seen for tens of millions, or even hundreds of millions, of years. “[It’s] pretty clear that times of high carbon dioxide— and especially times when carbon dioxide levels rapidly rose— coincided with the mass extinctions,” writes University of Washington paleontologist and End- Permian mass extinction expert Peter Ward. “Here is the driver of extinction.”
As civilization is busy demonstrating, supervolcanoes aren’t the only way to get lots of carbon buried in the rocks out into the atmosphere in a hurry. Today humanity busies itself by digging up hundreds of millions of years of carbon buried by ancient life and ignites it all at once at the surface, in pistons and power plants— the vast, diffuse metabolism of modern civilization. If we see this task to completion and burn it all— supercharging the atmosphere with carbon like an artificial supervolcano— it will indeed get very hot, as it has before. The hottest heat waves experienced today will become the average, while future heat waves will push many parts of the world into uncharted territory, taking on a new menace that will surpass the hard limits of human physiology.
If this comes to pass, the planet will return to a condition that, though utterly alien to us, has made many appearances in the fossil record. But warm times aren’t necessarily a bad thing. The dinosaur- haunted Cretaceous was significantly richer in atmospheric CO2, and that period was consequently much warmer than today. But when climate change or ocean chemistry changes have been sudden, the result has been devastating for life. In the worst of times, the earth has been all but ruined by these climate paroxysms as lethally hot continental interiors, acidifying, anoxic oceans, and mass death swept over the planet.
This is the revelation of geology in recent years that presents the most worrying prospect for modern society. The five worst episodes in earth history have all been associated with violent changes to the planet’s carbon cycle. Over time, this fundamental element moves back and forth between the reservoirs of biology and geology: volcanic carbon dioxide in the air is captured by carbon- based life in the sea, which dies and becomes carbonate limestone on the seafloor. When that limestone is thrust down into the earth, it’s cooked and the carbon dioxide is spit out by volcanoes into the air once more. And on and on. This is why it’s a cycle. But events like sudden, extraordinarily huge injections of carbon dioxide into the atmosphere and oceans can short-circuit this chemistry of life. This prospect is one reason why past mass extinctions have become such a vogue topic of late in the research community. Most of the scientists I spoke with over the course of reporting this book were interested in the planet’s history of near-death experiences, not just to answer an academic question, but also to learn, by studying the past, how the planet responds to exactly the sorts of shocks we’re currently inflicting on it.
This ongoing conversation in the research community is strikingly at odds with the one taking place in the broader culture. Today much of the discussion about carbon dioxide’s role in driving climate change makes it seem as though the link exists only in theory, or in computer models. But our current experiment— quickly injecting huge amounts of carbon dioxide into the atmosphere— has in fact been run many times before in the geological past, and it never ends well. In addition to the unanimous and terrifying projections of climate models, we also have a case history of carbon dioxide– driven climate change in the planet’s geologic past that we would be well advised to consult. These events can be instructive, even diagnostic, for our modern crises, like the patient who presents to his doctor with chest pains after a history of heart attacks.
But there’s a risk of stretching the analogy too far: Earth has been many different planets over its lifetime, and though in some salient and worrying ways our modern planet and its future prospects echo some of the most frightening chapters in its history, in many other ways our modern biocrises represent a one-off— a unique disruption in the history of life. And thankfully, we still have time. Though we’ve proven to be a destructive species, we have not produced anything even close to the levels of wanton destruction and carnage seen in previous planetary cataclysms. These are absolute worst-case scenarios. The epitaph for humanity does not yet have to include the tragic indictment of having engineered the sixth major mass extinction in earth history. In a world sometimes short on it, this is good news.
Excerpted From THE ENDS OF THE WORLD by Peter Brannen. Copyright ©2017 Peter Brannen. Reprinted by permission of Ecco, an imprint of HarperCollins Publishers.
This article was originally published on August 15, 2017.
This segment aired on August 15, 2017.