The Many Ends of Planet Earth

• The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth’s Past Mass Extinctions
• Peter Brannen
• HarperCollins (2017)

Opponents of action to curb global warming have long argued that climate change is natural, and happened long before humans ever discovered fire. So there’s no point in blaming ourselves, let alone trying to do something about it.

But as The Ends of the World points out, we are currently living in an ice age, and civilization has flourished in a 12,000-year-long interglacial period. Most interglacials last about 10,000 years, and without human activity the glaciers would now be building up, not melting away.

But even 10,000 years offer little real perspective on our present situation. Peter Brannen takes us back half a billion years and then forward to each of the five mass extinctions that life on Earth has endured. Each destroyed a rich and complex world, leaving few survivors to evolve and replace it. We are now supposedly in the Sixth Extinction, destroying species through hunting, habitat destruction, our sheer numbers and the climate change we’ve caused.

True enough, no doubt, but natural forces have been far more thorough than we could ever be.

Those forces, Brannen tells us, are familiar ones: CO2, geology and life itself. Usually, they stay in some kind of balance, but not always. Tectonic plates collide; volcanoes erupt, spewing CO2 and warming the atmosphere. Storms of acid rain erode rising mountain ranges, dragging more CO2 back into the sea, where it helps feed plankton that then die, carrying carbon to the sea floor, cooling the planet. Then the sea floor rises to form new mountain ranges and the cycle continues.

A 25-million-year disaster

Until it doesn’t. The Late Devonian extinction, 375 million years ago was a series of disasters stretching over 25 million years. Plants had finally moved onto land, forming the planet’s first soils. These washed into the sea, causing eutrophication just as they do today. Oxygen-free dead zones appeared in the oceans, while enormous forests absorbed up to 90 per cent of the CO2 in the atmosphere. That led to an ice age, killing more oceanic life and the forests themselves.

The end of the Permian era, 252 million years ago, very nearly finished off all life above the bacterial level. Lava not only flooded Siberia, it ignited gigantic coal beds, which exploded and released CO2 and methane.

Brannen says we emit about 40 gigatons of CO2 a year, and if we could burn every crumb and drop of fossil fuel our emissions would total about 5,000 gigatons. But the lavas of the Siberian Traps released something between 10,000 and 48,000 gigatons of carbon.

“In the tropics,” Brannen writes, “ocean temperatures skyrocketed from 25 C — similar to today’s oceans — to perhaps upwards of 40 C (104 F). This is the temperature of a hot tub, or as End-Permian expert Paul Wignall puts it, that of ‘very hot soup.’”

How to trigger a hypercane

Another expert, Jonathan Payne, tells Brannen that the oceans would have become so acidified that almost every organism in them would have died. Payne calculates that 40,000 gigatons of carbon would raise atmospheric CO2 levels from 300 parts per million (where they were in 1900) to 30,000 ppm. That in turn would trigger “hypercanes” — continent-sized storms with 500-mph winds.

It took 20 million years to recover from the End-Permian extinction. A new equilibrium emerged, complete with dinosaurs, and was then shattered by still more lava eruptions from the eastern U.S. up to the Gulf of St. Lawrence.

Brannen makes a good case that extinctions result from a mix of factors — eruptions, continental drift and the kind of atmosphere that living organisms and volcanoes create. The Alvarez theory argues that a small asteroid struck the Yucatan Peninsula 66 million years ago and finished off the dinosaurs. But others say even that wouldn’t have been enough without the concurrent eruptions of the Deccan Traps in India.

It’s fascinating to read Brannen’s accounts of these extinctions. As La Rochefoucauld famously observed, “We always find the strength to bear the misfortunes of others.” That’s especially true when the others are, say, placoderms — ocean predators “as long as a Winnebago.” Such creatures ruled their world for scores of millions of years, but we could never have evolved in their world. And if armoured dimwits could flourish for millions of years, humans should be able to look forward to at least as long a reign. After all, modern humans emerged just 300,000 years ago.

100,000 years to get back to 'normal'

But Brannen doesn’t stop with the fall of the dinosaurs and the triumph of the mammals. He points out that the catastrophes of the distant past dragged on for hundreds of thousands of years. The End-Permian is famous for wiping out almost all life in the eye blink of just 60,000 years. It took a long, long time to build up CO2 in the atmosphere, and a long time to get rid of it.

By contrast, we’ve boosted CO2 by over 30 per cent in a century. As well, we’re burning in decades the long-sequestered carbon that took millions of years to accumulate as coal, oil and natural gas.

Brannen estimates it will take 100,000 years of weathering just to bury the CO2 we’ve pumped into the air since the Industrial Revolution. In the meantime, the planet’s climate will be hotter and more turbulent than we’ve ever seen in our pleasant little interglacial.

Still, even human-caused heating will only postpone the next glaciation by a couple of hundred thousand years. The final end of the world, Brannen says, won’t arrive for another 1.3 billion years, when even bacteria die out.

And while we’re doing real damage to many species and habitats, the palaeontologists that Brannen talks to say we’re nowhere near inflicting a Sixth Extinction on the planet. As one puts it, you don’t have a mass extinction until you’re worried about rats and coyotes; if they go, almost everything else goes too.

An astounding run of dumb luck

If Brannen just wanted to make some points about modern climate change in the perspective of past and future disasters, this would be a good book. It becomes a much better book because he shifts perspective again. We like to think of past extinctions as necessary messes that cleared the way for us, the jewel in life’s crown. Brannen sees us as the beneficiaries of an astounding run of dumb luck.

Back in 2000, two American scientists published Rare Earth: Why Complex Life Is Uncommon in the Universe. They argued that few planets have all the conditions needed to permit life to arise, let alone evolve beyond the bacterial level. And as Brannen makes clear, even fewer planets can provide uninterruptedly benign conditions. In fact, the very conditions that permit life, like plate tectonics, also doom it.

This may help to explain why we have yet to pick up signals from alien civilizations: life on distant earth-like worlds almost never survives long enough to develop technically advanced civilizations. Whether from natural or self-inflicted catastrophe, intelligent aliens are mostly just another narrow band of fossils on their now-lifeless worlds.

We take our existence for granted, when it’s statistically almost impossible. Between nuclear weapons and anthropogenic climate change, we’re lengthening the odds against our survival still more.

If we were really intelligent, we’d see ourselves as the winners of the biggest Powerball lottery in the universe, a prize worth preserving. Instead, we seem intent on playing double or nothing with our whole stake. So far we’ve doubled and doubled again. But eventually we’ll turn one card too many, and the bacteria will repossess the planet. For a while.