If humans disappeared tomorrow, what would become of Earth? Writing in Discover, journalist Alan Weisman imagines a new epoch that would be tough on dogs and rats, but great for lichen.

Given the mounting toll of fouled oceans, overheated air, missing topsoil, and mass extinctions, we might sometimes wonder what our planet would be like if humans suddenly disappeared. Would Superfund hazardous waste sites revert to Gardens of Eden? Would the seas again fill with fish? Would our concrete cities crumble to dust from the force of tree roots, water, and weeds? How long would it take for our traces to vanish?

A good place to start searching for answers is in Korea, in the 155mile-long, 2.5-mile-wide mountainous Demilitarized Zone, or DMZ, set up by the armistice ending the Korean War. Aside from rare military patrols or desperate souls fleeing North Korea, humans have barely set foot in the strip since 1953. Before that, for 5,000 years, the area was populated by rice farmers who carved the land into paddies. Today, those paddies have become barely discernible, transformed into pockets of marsh, and the new occupants of these lands arrive as dazzling white squadrons of red-crowned cranes that glide over the bulrushes in perfect formation, touching down so lightly that they detonate no land mines. Next to whooping cranes, they are the rarest such birds on Earth. They winter in the DMZ alongside the endangered white-naped cranes, revered in Asia as sacred portents of peace.

Our dams might last centuries, but many rivers would return to old haunts within decades. [There was a great picture with this, but I cannot find this article online.]

As serenely natural as the DMZ now is, says Harvard biologist Edward O. Wilson, it would be far different if people throughout Korea suddenly disappeared. The habitat would not revert to a truly natural state until the dams that now divert rivers to slake the needs of Seoul’s more than 20 million inhabitants failed-a century or two after the humans had gone. But in the meantime, says Wilson, many creatures would flourish. Otters, Asiatic black bears, musk deer, and the nearly vanquished Amur leopard would spread into slopes reforested with young daimyo oak and bird cherry. The few Siberian tigers that still prowl the North Korean-Chinese borderlands would multiply and fan across Asia’s temperate zones. “The wild carnivores would make short work of livestock,” Wilson says. “Few domestic animals would remain after a couple of hundred years. Dogs would go feral, but they wouldn’t last long: They’d never be able to compete.”

If people were no longer present anywhere on Earth, a worldwide shakeout would follow. From zebra mussels to fire ants to crops to kudzu, exotics would battle with natives. In time, says Wilson, all human attempts to improve on nature, such as our painstakingly bred horses, would revert to their origins. If horses survived at all, they would devolve back to Przewalski’s horse, the only true wild horse, still found in the Mongolian steppes. “The plants, crops, and animal species man has wrought by his own hand would be wiped out in a century or two,” Wilson says. In a few thousand years, “the world would mostly look as it did before humanity came along-like a wilderness.”

It wouldn’t take long for nature to undo even the likes of a New York City. Jameel Ahmad, civil-engineering department chairman at Cooper Union College in New York, says repeated freezing and thawing would split cement within a decade, allowing water to seep in. As it froze and expanded, cracks would widen. Soon, weeds such as mustard and goosegrass would invade. With nobody to trample seedlings, New York’s prolific exotic, the Chinese ailanthus tree, would take over. Within five years, says Dennis Stevenson, senior curator at the New York Botanical Garden, ailanthus roots would heave up sidewalks and split sewers.

That would exacerbate a problem that already plagues New York-rising groundwater. There’s little soil to absorb it or vegetation to transpire it, and buildings block the sunlight that could evaporate it. With the power off, pumps that keep subways from flooding would be stilled. As water sluiced away soil beneath pavement, streets would crater.

Eric Sanderson of the Bronx Zoo Wildlife Conservation Society heads the Manhattan Project, a virtual recreation of pre-1609 Manhattan. He says there were 30 to 40 streams in Manhattan when the Dutch first arrived. If New Yorkers disappeared, sewers would clog, some natural watercourses would reappear, and others would form. Within 20 years, the water-soaked steel columns that support the street above the East Side’s subway tunnels would corrode and buckle, turning Lexington Avenue into a river.

New York’s architecture isn’t as flammable as San Francisco’s clapboard Victorians, but within 200 years, says Steven Clemants, vice president of the Brooklyn Botanic Garden, tons of leaf litter would overflow gutters as pioneer weeds gave way to colonizing native oaks and maples in city parks. A dry lightning strike, igniting decades of uncut, knee-high Central Park grass, would spread flames through town.

As lightning rods rusted away, roof fires would leap among buildings into paneled offices filled with paper. Meanwhile, native Virginia creeper and poison ivy would claw at walls covered with lichens, which thrive in the absence of air pollution. Wherever foundations failed and buildings tumbled, lime from crushed concrete would raise soil pH, inviting buckthorn and birch. Black locust and autumn olive trees would fix nitrogen, allowing more goldenrods, sunflowers, and white snakeroot to move in along with apple trees, their seeds expelled by proliferating birds. Sweet carrots would quickly devolve to their wild form, unpalatable Queen Anne’s lace, while broccoli, cabbage, Brussels sprouts, and cauliflower would regress to the same unrecognizable broccoli ancestor. Meanwhile, coyotes would invade Central Park, and deer, bears, and finally wolves would follow.

Missing, however, would be all fauna that have adapted to humans. The invincible cockroach, an insect that originated in the hot climes of Africa, would succumb in unheated buildings. Without garbage, rats would starve or serve as lunch for peregrine falcons and red-tailed hawks.

It’s unclear how long animals would suffer from the urban legacy of concentrated heavy metals. Over many centuries, plants would take these up, recycle, redeposit, and gradually dilute them. The time bombs left in petroleum tanks, chemical plants, power plants, and dry-cleaning plants might poison the earth beneath them for eons. Places like the Indian Point nuclear power plant, 35 miles north of Times Square, would dump radioactivity into the Hudson River long after the lights went out.

Old stone buildings in Manhattan, such as Grand Central Station or the Metropolitan Museum of Art, would outlast every modern glass box, especially with no more acid rain to pock their marble. Still, at some point thousands of years hence, the last stone walls-perhaps chunks of St. Paul’s Chapel on Wall Street, built in 1766 from Manhattan’s own hard schist would fall. Three times in the past 100,000 years, glaciers have scraped New York clean, and they’ll do so again. The mature hardwood forest would be mowed down. On Staten Island, Fresh Kills’ four giant mounds of trash would be flattened, their vast accumulation of stubborn PVC plastic and glass ground to powder. After the ice receded, an unnatural concentration of reddish metal-remnants of wiring and plumbing-would remain buried in layers. The next toolmaker to arrive or evolve might discover it and use it, but there would be nothing to indicate who had put it there.

Layers below the planet's surface, our wiring and plumbing would long outlive our memory. [Another great picture was above this quote.]

Even our total disappearance could never bring all megafauna species back. In a glass case in his laboratory, paleoecologist Paul S. Martin at the University of Arizona keeps a lump of dried dung he found in a Grand Canyon cave, left by a sloth weighing 200 pounds. That would have made it the smallest of several North American ground sloth species present when humans first appeared on this continent. The largest was as big as an elephant and lumbered around by the thousands in the woodlands and deserts of today’s United States. What we call pristine today, Martin says, is a poor reflection of what would be here if Homo sapiens had never evolved.

“America would have three times as many species of animals over 1,000 pounds as Africa does today,” he says. An amazing megafaunal menagerie roamed the region: Giant armadillos resembling armor-plated autos; bears twice the size of grizzlies; the hoofed, herbivorous toxodon, big as a rhinoceros; and saber-toothed tigers. A dozen species of horses were here, as well as the camel-like litoptern, giant beavers, giant peccaries, woolly rhinos, mammoths, and mastodons. Climate change and imported disease may have killed them, but most paleontologists accept the theory Martin advocates: “When people got out of Africa and Asia and reached other parts of the world, all hell broke loose.” He is convinced that people were responsible for the mass extinctions because they commenced with human arrival everywhere.

Without people, most excess industrial carbon dioxide would dissipate within 200 years, cooling the atmosphere. With no further chlorine and bromine leaking skyward, within decades the ozone layer would replenish, and ultraviolet damage would subside. Eventually, heavy metals and toxins would flush through the system; a few intractable PCBs might take a millennium.

During that same span, every dam on Earth would silt up and spill over. Rivers would again carry nutrients seaward, where most life would be, as it was long before vertebrates crawled onto the shore. Eventually, that would happen again. The world would start over.

From an article by Alan Weisman that was originally published in Discover. The story also appears in the book Best American Science Writing 2006. Weisman’s own book on the subject, The World Without Us, will be published next year by Thomas Dunne Books/St. Martin’s Press.

Interesting. Last night I watched an Animal Planet show speculating on what would be the evolution of species were we all destroyed. They speculated out to 200 million years. Apparently scientists speculate that Squids would evolve into land animals and that some could become sentient. It was a fascinating trip of the mind into a possible distant future.

Fascinating, Beamer! Thanks for posting this article.

I thought so too!



You know, with all of the strife in Africa, certain countries in Asia and elsewhere, I have wondered if we could designate areas in the US where we could place wild animals that are endangered, such as tigers.