The Anthropocene may be an event, not an era

An informative article by Peter Brannen in The Atlantic contrasts the plausible duration of the geological evidence of human civilization against the scale at which we normally designate geological epochs. It suggests convincingly that the idea of an Anthropocene epoch is misplaced:

What humans are doing on the planet, then, unless we endure for millions to tens of millions of years, is extremely transient. In fact, there exists a better word in geology than epoch to describe our moment in the sun thus far: event. Indeed, there have been many similarly disruptive, rapid, and unusual episodes scattered throughout Earth history — wild climate fluctuations, dramatic sea-level rises and falls, global ocean-chemistry disasters, and biodiversity catastrophes. They appear as strange lines in the rock, but no one calls them epochs. Some reach the arbitrary threshold of “mass extinction,” but many have no name. Moreover, lasting only a few tens of thousands to hundreds of thousands of years in duration, they’re all considered events. In our marathon of Earth history, the epochs would occasionally pass by on the side of the road like towns, while these point-like “events” would present themselves to us only fleetingly, like pebbles underfoot.

Fifty-six million years ago, the Earth belched 5,000 gigatons of carbon (the equivalent of burning all our fossil-fuel reserves) over roughly 5,000 years into the oceans and atmosphere, and the planet warmed 5 to 8 degrees Celsius. The warming set off megafloods and storms, and wiped out coral reefs globally. It took the planet more than 150,000 years to cool off. But this “Paleocene-Eocene Thermal Maximum” is considered an event.

Thirty-eight million years before that, buried in the backwaters of the late Cretaceous, CO2 jumped as many as 2,400 parts per million, the planet warmed perhaps 8 degrees Celsius, the ocean lost half its oxygen (in our own time, the ocean has lost a — still alarming — 2 percent of its oxygen), and seawater reached 36 degrees Celsius (97 degrees Fahrenheit) over much of the globe. Extinction swept through the seas. In all, it took more than half a million years. This was Cretaceous Oceanic Anoxic Event 2. Though it was no epoch, if you had been born 200,000 years into this event, you’d die roughly 300,000 years before it was over.

A similar catastrophe struck 28 million years before, in the early Cretaceous, and again 60 million years earlier still in the Jurassic. And, again, 201 million years ago. And halfway through the Triassic, 234 million years ago. And 250 million, 252 million, and 262 million years ago. The first major mass extinction, 445 million years ago, took place in multiple pulses across a million years. An event. The second major mass extinction, 70 million years later, took place over 600,000 years — 400,000 years longer than the evolutionary history of Homo sapiens. These are transformative, planet-changing paroxysms that last on the order of hundreds of thousands of years, reroute the trajectory of life, and leave little more than strange black lines in the rocks, buried within giant stacks of rocks that make up the broader epochs. But none of them constitute epochs in and of themselves. All were events, and all — at only a few tens of thousands, to hundreds of thousands of years — were blisteringly short.

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Until we prove ourselves capable of an Anthropocene worthy of the name, perhaps we should more humbly refer to this provisional moment of Earth history that we’re living through as we do the many other disruptive spasms in Earth history. Though dreadfully less catchy, perhaps we could call it the “Mid-Pleistocene Thermal Maximum.” After all, though the mammoths are gone, their Ice Age is only on hold, delayed as it is for a few tens of thousands of years by the coming greenhouse fever. Or perhaps we’re living through the “Pleistocene Carbon Isotope Excursion,” as we call many of the mysterious global paroxysms from the earliest era of animal life, the Paleozoic. Or maybe we’re even at the dawning of the “Quaternary Anoxic Event” or, God forbid, the “End-Pleistocene Mass Extinction” if shit really hits the fan in the next few centuries. But please, not the Anthropocene. You wouldn’t stand next to a T. rex being vaporized 66 million years ago and be tempted to announce to the dawning of the hour-long Asteroidocene. You would at least wait for the dust to settle before declaring the dawn of the age of mammals.

Instead of our cities or our plastics or our radioactive isotopes, the author suggests: “The most enduring geological legacy, instead, will be the extinctions we cause.” Humanity’s impact may be more perceptible in what we have taken away from the totality of life, instead of in what we have built or even the pollution we created.

Related:

• Is runaway climate change possible? Hansen’s take
• Limiting total historical human emissions
• Environmentalism and the anthropocene
• Environmentalism and ‘breathing underwater’