The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions

by Peter Brannen

the Cambrian Explosion. When this spectacular supernova of biology detonated, the world of animal life—creatures that move around and eat other organisms for a living—was truly born.

A sentiment exists—particularly among nonscientists—that the idea of humans seriously disrupting the planet on a geological scale is mere anthropocentric hubris. But this sentiment misunderstands the history of life. In the geological past, seemingly small innovations have reorganized the planet’s chemistry, hurling it into drastic phase changes. Surely humans might be as significant as the filter-feeding animals of the Cambrian Explosion.

Apparently the planet can withstand a tremendous punch or two with good humor. It must take something truly dreadful to knock it over.

That the most stunning period of biodiversification in the history of life took place at the same time as the planet was being pelted by meteors and unleashing some of its most powerful volcanic explosions ever is a testament to the living world’s resilience. This confluence might even indicate that a little disturbance is a good thing for life.

Not very long ago, the Northern Hemisphere was smothered by ice and the sea level was 400 feet lower than it is today. Right now, far offshore at the bottom of the Atlantic Ocean, sea robins and cod tend to mastodon and woolly mammoth graveyards. Their tusks are pulled up by scallop dredgers on George’s Bank and in the Gulf of Maine. Though they’re found at the bottom of the ocean, these were not amphibious mammoths. Instead, they roamed a vast coastal plain on what was dry Atlantic continental shelf before the great ice sheets melted and raised the seas hundreds of feet. Underwater canyons now teeming with sea life were rivers and scenic estuaries cutting through the dry seabed, and all this was only a couple of hundred human generations ago—essentially now from a geologic standpoint.

Surprisingly, our ice age—which once hosted woolly mammoths and saber-toothed cats—isn’t over; it’s just on recess. Throughout the ice age of the past few million years, there have been dozens of so-called interglacials—brief windows of warmth, lasting only a few thousand years, when it gets warmer, the ice rapidly melts and retreats to the poles (where it is today), and the seas rise by hundreds of feet. We’re currently in one of these brief respites from the cold, but interglacials don’t usually last very long. This is all caused by the periodic wobble of the planet in space and the rhythmic changes to its orbit, which nudges the planet in and out of the sunlight, alternately locking much of the Northern Hemisphere in ice and then thawing it over and over again, like a geological metronome. The thaws often last fewer than 10,000 years before the great ice sheets at the poles begin to advance on the continents once more, sending the seas plummeting hundreds of feet.

There have been at least twenty such balmy intermissions like our own sprinkled throughout the past few million years of our ice age. But unlike the many previous warm interglacials, civilization—and all of recorded human history—happened to arise during this one. Our few millennia in the sunshine are up, and if it weren’t for us, we might be just about ready to leave this agreeable little interregnum and jump back into the ongoing deep freeze of the Pleistocene for 100,000 bitterly cold years.

the world we take for granted was, until very recently, frozen solid. As I write this in Massachusetts, the evidence surrounds me, plain to see. Massive boulders unceremoniously dropped by the glaciers dot the deep woods, town centers, and beaches throughout New England. Kettle ponds mark the spots where large solitary hunks of ice, orphaned by the great ice sheets, were left behind to melt in their tracks. The winter world is evident in the grooved lines, called striations, etched in the bedrock of the mountains of New Hampshire, where mile-thick grindstones of ice advanced and retreated, scraping bare the scenery behind them. Long Island, Block Island, Cape Cod, Martha’s Vineyard, and Nantucket are all essentially dump heaps of rocks and sand where the ice sheets pushed south, sputtered and spewed their guts out onto the tundra. Like the many unremembered islands and sand spits that came and passed in the interglacials before, these features are all being quickly eroded away to nothing.

the Finger Lakes of New York were carved by massive glaciers, while the Great Lakes are basically the world’s largest puddles, left when the ice sheets melted only a few thousand years ago. The most dramatic example might be in the epic Channeled Scablands of eastern Washington, which were carved by truly mind-blowing cyclical floods called jökulhlaups. During the last glacial cycle, as a massive ice sheet pushed into Idaho, the ice blocked the Clark Fork River and created an enormous dammed lake in Montana, six times the volume of Lake Erie. As the lake grew and grew, it eventually reached a depth of 600 feet, at which point the obstructing ice started to float. As water continued to gnaw at cracks at the base of the ice dam, the lake suddenly failed and the whole system collapsed in a catastrophic flood that—all at once—released ten times the flow of all the rivers in the world. Waves leaving ripple marks 450 feet long and carrying 30-foot boulders crashed through eastern Washington, tearing up the bedrock, sculpting canyons, and leaving the southeast corner of the state barren of soil and vegetation. When the glacial dam began to re-form, the lake began to fill once more, and eventually it burst again. And again. This catastrophe repeated itself perhaps as many as sixty times between 15,300 and 12,000 years ago. This was right about when the first Americans were wandering into the continent, and perhaps some unlucky few witnessed, and even perished, in these local apoca...

But our ice age was so recent that some places like Alaska and Canada are literally still bouncing back up from the removal of oceans of ice overhead—that is, the landmass is actually rising, year after year, like your seat cushion after you stand up. The height of this last ice age is popularly conceived to be a distant part of the planet’s past. But from a geological perspective, it was an eyeblink ago. If all of Earth’s history were represented by a 24-hour clock, it was half a second before midnight.*

Today the concern is about injecting carbon dioxide into the atmosphere too quickly and creating a global hothouse climate. But just as problematic can be quickly plummeting levels of carbon dioxide, which can create an icehouse climate instead. However strange it seems at first, the creation of the Appalachians might hold the key to explaining this punishing glaciation that nearly wiped out life on Earth.

The modern Appalachians began to form in the Ordovician* when a volcanic island chain with an insatiable appetite for ocean crust ate its way across the sea before plowing into the eastern edge of North America. This train wreck is visible throughout the mangled rocks of New England.

If MacDonald is right, the creation of the Appalachians is responsible for a precipitous drawdown in carbon dioxide and the brief ice age that nearly wiped clean the evolutionary slate 445 million years ago.

We take for granted the shape of our world and the position of the continents—the familiar geography that seems as eternal as the order of the planets.* But this arrangement is temporary: it isn’t how the planet has been and it isn’t how it will be.

Today plants and animals are already shifting their ranges in response to man-made changes in climate. In 2012 the US Department of Agriculture was forced to update its vegetation maps to reflect the northward shift in plant life under way in the United States. Lobster fishermen south of Massachusetts have all but shuttered their businesses as the crustaceans steadily march northward to track the cooler bottom waters they prefer.