Diprotodon optatum, the largest marsupial ever. Photo: AFP

“The bolide arrived from the southeast, traveling at a low angle relative to the earth, so that it came in not so much from above as from the side, like a plane losing altitude.” We are in Chapter Four here, and our tale, already great, is getting gripping. The thing in the sky is six miles wide, about the length of Manhattan from Houston Street to Harlem. It is moving at 45,000 miles per hour, roaring through the atmosphere, burning up bits of itself as it goes, and then there is no more atmosphere to roar through and it slams into the earth. The impact releases a billion times more energy than the atomic bombs dropped on Japan. The surface of the planet boils from the heat. Debris ignites a string of firestorms. Ash from the conflagration combines with the collision’s massive mushroom cloud to blot out the sun. Day turns to night, light to dark, heat to cold, photosynthesis to pffft. Some say the world will end in fire. Yes. Some say the world will end in ice. That, too.

We appear to be in a post-apocalyptic novel, but, in fact, we are in fact. Sixty-six million years ago, an asteroid crashed into the Yucatán Peninsula, leaving behind a crater 110 miles wide and twenty miles deep and a colossally larger hole in the tree of life. The impact and its after­effects wiped out an estimated 75 percent of species, including, most famously, all non-avian dinosaurs. That event, the end-­Cretaceous extinction, is one of six massive die-offs in the history of the planet. Five of them happened in the distant past: 450 million, 375 million, 252 million, 200 million, and 66 million years ago. The sixth one is happening right now.

Environmental issues are not known for their entertainment value: Pollution is dreary, energy wonky, climate change depressing. Perversely, extinction, which should be the most existentially troubling, is something of an exception. That’s thanks almost entirely to the end-Cretaceous, whose outer space–meets–T. Rex plot could have been written by H. P. Lovecraft, or 10-year-old boys, or the folks who brought us Snakes on a Plane.

In print, at least, the New Yorker writer Elizabeth Kolbert shares none of those sensibilities. But in her new book, The Sixth Extinction, she makes a page-turner out of even the most sober and scientifically demanding aspects of extinction. Combining a lucid, steady, understated style with some enviable reporting adventures (chasing frogs in the Panamanian jungle, watching coral spawn in the Great Barrier Reef), she produces a book that is both serious-­minded and invites exclamation points into its margins. You will finish The Sixth Extinction knowing a lot about the history and ecology of mass die-offs. You will also know that the Bikini Atoll once went by the less wearable name of Eschscholtz; that certain frogs “survive the winter frozen solid, like popsicles”; and that, if you were a dinosaur in Canada when that asteroid hit the Yucatán, you had approximately two minutes to live.

Those facts—not just the fun ones, the sum total—supply the substance but also the tenor of this book. For a work of what we might term mid-apocalyptic nonfiction, The Sixth Extinction is remarkably restrained. Unlike in her last book, Field Notes From a Catastrophe, Kolbert does not embroil herself here in the politics of environmental disaster. Instead, she exposes its ecological mechanisms, and, in what must be among the most studiously neutral sentences ever written, expresses the hope that readers “will come away with an appreciation of the truly extraordinary moment in which we live.” By which she means, of course, the truly extraordinary moment in which so much around us begins to die.

Back in the day, humans went about exterminating other creatures in straightforward fashion—by slaughtering them, one by one. Kolbert recounts the story of the great auk, a penguinlike bird that had the misfortune of being tall, tubby, edible, burnable (all that body fat), nicely feathered (handy for mattresses), and, alack, unable to fly. By the mid-1800s, the world was, unsurprisingly, auk-less. Many other creatures met similar fates, including the passenger pigeon, the Atlas bear, and the famous dodo, which we had eaten to death by around 1660. They were far from the first. Credible evidence suggests that our primitive ancestors hunted to extinction nearly all the megafauna of the Pleistocene: woolly rhinos, cave bears, giant sloths, aurochs, mastodons, mammoths.

Humans still overhunt and overfish other species today, so much so that ecologists refer to us as “overkillers.” But in recent centuries, the causal chain of extinction has attenuated. Destroying a habitat is a less direct way of killing an animal than braining it. Disseminating pollutants via air or ocean or groundwater is less direct still. Climate change might be the most indirect way of all.

These factors interact, of course. In his 1996 book The Song of the Dodo, David Quammen observed that if you destroy most of a habitat and leave only a small patch of wilderness behind, you have effectively created an island—and islands, for complex ecological reasons, sustain far fewer species and far more extinctions than mainlands. Now watch things get complicated. At the same time that our logging, mining, farming, road-building, suburban-sprawling species is turning the entire planet into an archipelago, “global trade and travel do the reverse: they deny even the remotest islands their remoteness.” That’s Kolbert, who goes on to note that every day, some 10,000 species hitch rides around the world in ballast water alone, threatening local critters all along the way. In Hawaii, a new invasive species establishes itself each month. To put that in perspective: Before the arrival of the invasive species known as humans, a new one established itself roughly once every 10,000 years.

Now add climate change, which interacts disastrously with the world’s more island-y aspects. As weather patterns shift, species that can move do, tracking whatever conditions they are best adapted for—colder or warmer temperatures, rainier or dryer locations. But in a world carved into fragments, such movement is impossible. “One of the defining features of the anthropocene,” Kolbert writes, referring to our current, human-dominated geological era, “is that the world is changing in ways that compel species to move, and another is that it’s changing in ways that create barriers—road, clear-cuts, cities—that prevent them from doing so.”

Throw in overkilling, ocean acidification, and pollution, and the losses start to look catastrophic. In Kolbert’s accounting, we stand to shed one in three species of coral, one in four mammals, one in five reptiles, one in six birds, and heaven only knows how many insects and plants. In all these cases, scientists quibble about the exact figures—but, as Kolbert notes, not about the order of magnitude. We might lose 10 percent of species, or we might lose 30 percent of species. But nobody believes we will lose 1.3 percent or 0.31 percent.

Tolerate for a moment a tautology: If an asteroid causes a mass extinction, the extinction was caused by the asteroid. If humans cause a mass extinction, the extinction was caused by … what? Rocks, spears, traps, guns, coal plants, copper mines, DDT, okay, but those are ultimately unsatisfying answers. They may be the means of annihilation, we may be the cause, but what is it that causes us to be so destructive?

In the penultimate chapter of her book, Kolbert tackles that question by examining one particularly troubling extinction. The Neanderthals were extremely similar to us; less than 0.3 percent of our DNA diverges. But they did not venture into new terrain, they did not significantly alter the terrain they were already in, and they certainly did not make a bonsai project out of the tree of life. They had, in Kolbert’s words, “no more impact on their surroundings than any other large vertebrate.”

Meanwhile, we Homo sapiens traveled out of Africa en route to everywhere, encountered the Neanderthals in Europe, had sex with them, and, directly or through competition for resources, exterminated them. Some 30,000 years later, we rediscovered them, via their remains, in a cave in limestone cliffs in a valley in Germany. That cave no longer exists. Those cliffs no longer exist. We quarried the limestone, smelted it with coke and iron ore, and converted it to steel.

What species does this? Only ours. Somewhere along the line, thanks to some twist in that 0.3 percent of uniquely human DNA, we became the sort of creatures who could level cliffs and turn stone to steel; “the sort of creature,” Kolbert writes, “who could wipe out its nearest relative, then dig up its bones and reassemble its genome.”

In the end, and somewhat despite itself, The Sixth Extinction is more about that peculiar creature than about the millions of others vanishing from the planet it has so thoroughly colonized. For all the exquisite attention Kolbert pays to bats and auks and ammonites, what emerges most clearly from her book is the Janus face of the human species. We killed those auks; we also traced a slender layer of clay back 66 million years to identify the asteroid that killed those ammonites. This is our freakish, wondrous, terrifying signature: We can explore a planet, admire it, domesticate it, destroy it.

Can we also save it? Kolbert’s tone, crystalline, reserved, sits like a pane of glass in a darkened window. It could be that dwelling in geologic time, as you must do to write about extinction, is good for perspective but bad for action; the arc of the actual universe is so long it bends toward fatalism. Human time, by contrast, is good for acting but bad for seeing. It is into the chasm between these two timescales that species are dropping like flies.

Kolbert tells all this like it is, and like it almost certainly will be. But she declines to tell us how to feel about it or what to do. Virtually the entirety of what this book has to say about feeling and doing shows up in two lines three pages from the end, after we understand exactly how depauperate we have rendered our planet. “It doesn’t matter much whether people care or don’t care,” Kolbert writes. “What matters is that people change the world.” The first sentence stings. The second unsettles; she must surely have chosen its undertones. “Change the world” is our stock summons to positive action. It hangs in these final pages unresolved, stuck between its major and her minor key.

The Sixth Extinction: An Unnatural History

By Elizabeth Kolbert

Henry Holt.

352 pages. $28.

*This article originally appeared in the February 17, 2014 issue of New York Magazine.

