The World Without Us

Sandy-haired Doug Erwin looks improbably boyish for so distinguished a scientist. When he dismisses life-on-Earth’s closest brush with total annihilation, however, his smile isn’t flippant but thoughtful—the result of decades of poring over West Texas mountains, old Chinese quarries, and ravines in Namibia and South Africa to puzzle out what exactly happened. He still doesn’t know for sure. A million-year-long volcanic eruption through enormous coal deposits in Siberia (then part of Pangea, the single supercontinent) flooded the land with so much basalt magma— in places, it was more than three miles thick—that CO₂ from vaporized coal may have glutted the atmosphere and sulfuric acid may have rained from the skies. The coup de grâce may have been an asteroid even bigger than the one that did in the dinosaurs much later; it apparently collided with the piece of Pangea we now call Antarctica.

Whatever it was, over the next few million years, the most common vertebrate was a microscopic-toothed worm. Even insects suffered a mass collapse. This was a good idea?

“Sure. It made way for the Mesozoic Era. The Paleozoic had been around for nearly 400 million years. It was fine, but it was time to try something new.”

Following the Permian’s fiery end, the few survivors had little competition. One of them, a half-dollar-sized, scalloplike clam called claraia, became so abundant that its fossils today literally pave rocks in China, southern Utah, and northern Italy. But within 4 million years, they and most other bivalves and snails that boomed after the mass extinction died out themselves. They were victims of more mobile opportunists such as crabs, who’d had minor roles in the old ecosystem, but suddenly—at least by the geologic clock—had a chance at creating new niches in a fresh new system. All it took was evolving a claw to crack open mollusks that couldn’t flee.

The world took off in a different direction—one characterized by active predators—that went from near nothingness to the lush kingdom of dinosaurs. While that was happening, the supercontinent split into pieces that gradually dispersed around the globe. When, after 150 million more years, that other asteroid hit what is now Mexico’s Yucatan Peninsula, and dinosaurs proved too big to hide or adapt, it was time to start over yet again. This time, another agile minor character, a vertebrate called Mammalia, saw a chance to make its move.

Might the current explosion of extinctions—invariably pointing to a sole cause, and not an asteroid this time—suggest that a certain dominant mammal’s turn may be coming to an end? Is geologic history striking again? Doug Erwin, the extinction expert, works on such a vast timescale that the few million years of our Homo species’ life span is almost too short for him to contemplate. Again, he shrugs.

“Humans are going extinct eventually. Everything has, so far. It’s like death: there’s no reason to think we’re any different. But life will continue. It may be microbial life at first. Or centipedes running around. Then life will get better and go on, whether we’re here or not. I figure it’s interesting to be here now,” he says. “I’m not going to get all upset about it.”

If humans do stick around, University of Washington paleontologist Peter Ward predicts that agricultural land will become the biggest habitat on Earth. The future world, he believes, will be dominated by whatever evolves from the handful of plants and animals we’ve domesticated for food, work, raw materials, and companionship.

But if humans were to go tomorrow, enough wild predators currently remain to out-compete or gobble most of our domestic animals, though a few feral exceptions have proved impressively resilient. The escaped wild horses and burros of the American Great Basin and Sonoran Desert essentially have replaced equine species lost at the end of the Pleistocene. Dingoes, which polished off Australia’s last marsupial carnivores, have been that country’s top predator for so long that many down under don’t realize that these canines were originally companions to Southeast Asian traders.

With no large predators around other than descendants of pet dogs, cows and pigs will probably own Hawaii. Elsewhere, dogs may even help livestock survive: sheep ranchers in Tierra del Fuego often swear that the shepherding instinct is so deeply bred in their kelpie dogs that their own absence would be immaterial.