What Would Really Happen if Thanos Erased Half of All Life on Earth?

What Would Really Happen if Thanos Erased Half of All Life on Earth?
Illustration: Benjamin Currie (Gizmodo)
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Unless you’ve been hiding under a rock for the past year, you’ll know that the end of Avengers: Infinity War was a rather bleak affair.

To recap: Thanos managed to gather all of the Infinity Stones, complete the gilded gauntlet of doom, and snap his fingers, wiping out half of all life in the universe as he did so. But while you might think this indiscriminate erasure would trigger an ecological catastrophe, after consulting with scientists who have been wondering the same thing, it turns out that life is surprisingly resilient to the Mad Titan’s plans. Still, certain at-risk species could be pushed to extinction, and in some parts of the world, there could be a fair deal of ecological chaos.

The snapture didn’t just wipe out 50 percent of life, chosen at random, but–as confirmed by Kevin Feige, the president of Marvel Studios–it turned exactly half of the population of each individual species to dust. It wasn’t just half of all humans that disappeared, but half of all giraffes, of all sunflowers, of all Salmonella enterica bacteria, and so on. (The jury is out on viruses, but if half of those disappeared too then we can finally classify them as “life” and be done with it.)

The entire point of this mass murder was to free the remaining populations of sentient life from the burden of not having enough resources to go around, something that led to a societal collapse on Thanos’ homeworld. This, as it happens, is “a terrible idea on many levels,” Ken Lacovara, a paleontologist at Rowan University who has studied a different mass dying, the catastrophic event 66 million years ago that wiped out the dinosaurs, told Earther.

On the most basic level, it’s a bad idea because it won’t stick.

Humans have been undergoing exponential population growth for their entire history. In 1960, the human population hovered around three billion. Then, by the year 2000, another 3 billion of us had appeared. If you wiped out half of all humans, in another 40 years, we’d likely be back to the same population numbers.

The same applies to most species, said Lacovara. Historically, companies that harvested seals, whales and other animals tended to wipe out half the population immediately when they moved into a new area. In most cases, he said, a 50 percent cull would put those animals at their maximum rate of population growth–at least, until they reach numbers that the environment can no longer sustain.

With that in mind, the snaptastrophe is “not a strategy that would produce long-term population effects in the way Thanos intended,” said Lacovara. It might, however, produce some strange changes to the sorts of lifeforms that rule the various corners of the world.

Janet Hoole, an expert in animal behavior and human evolution at Keele University, explained that there will be a species imbalance depending on survival strategies. Those that have plenty of young and don’t spend much time on parental care, ensuring rapid reproduction, will be able to outcompete species that have fewer offspring, less often, but put more resources into them.

That means insects, as well as fast-reproducing critters like kangaroos, rats and rabbits, likely would do extremely well. A frog, ecologist James Faulconbridge noted, can produce around 20,000 eggs in a single season, and although a large number of these will fall to predation, they could potentially easily restore their population size within a year. Mosquitos, Lacovara grimly noted, would be back to full strength within a single summer.

Other slower-growing species, like tigers, will spring back at a comparatively glacial pace. “Halving the already decimated tiger population would push them closer into the extinction vortex which is already threatening them,” Faulconbridge said.

And some may not make it at all. “For species on the brink, it would put them over the threshold for sure,” Lacovara said. He pointed to Felis margarita, a sand cat that lives in North Africa and pockets of the Middle East, and which likely numbers in the double-digits. Take out half, then it may be too hard for them to find each other to breed.

The same might go for the 50 Javan rhinoceroses and the 23 Hainan gibbons left in the wild, noted Anthony Caravaggi, a conservation biologist at the University of South Wales. Apart from fewer breeding opportunities, the snapture would leave these animals more vulnerable to inbreeding, random weather events, disease, hunting and poaching.

Hoole explained that those swiftly breeding beasties would be able to slip into the spaces vacated not just within their own habitats, but into the habitats left vacated by other, rarer species. “The end result would be a simplified global ecosystem with rare animals becoming rarer and less genetically diverse,” Hoole told Earther.

There is also a chance that predator-prey relationships, like those between desert lions and giraffes, or mutualistic relationships like that of bees and flowers, could be thrown out of whack. It’s highly speculative as to what might happen in each pairing, though. “These are famously complex and inter-related cycles,” Faulconbridge said, adding that in this mess, it would be “very, very difficult to predict the overall winners and losers.”

Ben Libberton, a microbiologist and science communicator, wondered what might happen to Earth’s bacteria. People–huge vessels of trillions of microbes–may be okay, as illustrated by the fact that we regularly take antibiotics that can potentially kill off a huge proportion of their gut bacteria. Still, as the composition varies from person to person, a significant cull could perhaps allow for the outgrowth of bacteria previously suppressed by all the competition, which could mess with the delicate equilibrium in the gut.

“If this happens globally, it’s likely that some ecosystems would be okay but others would suffer,” Libberton told Earther. His main concern would be microbes in the soil that drive nutrient cycling, as well as those in on land and in the ocean that fix nitrogen. If half of them were suddenly removed and they didn’t quickly regain their current numbers, this could be problematic for the life that relies on those nutrients, beginning with plants.

Still, whether you’re looking at macro- or microbiology, most experts seem to agree the snapocalypse is nothing compared to what has happened to life in the past.

Alfio Alessandro Chiarenza, a doctoral researcher of paleontology at Imperial College London, said the fossil record clearly demonstrates that things like major asteroid impacts, prolonged volcanic eruptions, and rapid climate change are the real killers, not marauding menaces from Titan. The Great Dying—the 252-million-year-old mass extinction triggered by volcanically-induced climate change—killed off as much as 96 percent of all marine species.

“Life was almost completely annihilated,” he said. Those that survived took advantage of the bounty of resources left available to them.

Lest we forget, unchecked pollution, environmental degradation and rapid human-caused climate change are triggering a precipitous decline in a myriad of lifeforms across the world today. That makes a comparison with the snapture rather tempting, but it’s tricky, because there are varying reports on what the current rate of species extinction is, explained Emma Dunne, a doctoral researcher in paleontology at the University of Birmingham.

Regardless, from coral to amphibians, few ecologists would disagree that things are getting worse for plenty of lifeforms. Dunne suspects that the snapocalypse wouldn’t be anywhere near as bad as what we ourselves are causing. “The current biodiversity crisis is almost painful to think about,” she said, adding that populations are often cruelly driven to extinction, most often by human activities.

There’s a chance that the snap of doom might even help some critically endangered species out. Faulconbridge noted that the loss of half of all humans would probably be a boost, at least temporarily, to many species currently squeezed into vanishing and degraded habitats. But assuming Thanos wasn’t thinking of the imperiled western lowland gorilla when he was fishing for those Infinity Stones, it’s safe to say that his plan wouldn’t achieve his grandiose, twisted, aims.

It would, nevertheless, cause plenty of pointless trauma and provide an excuse for Captain America to continue staring broodingly into the middle distance.