Thanos in Avengers: Infinity War
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Credit: Marvel Studios

Science Behind the Fiction: The real-world consequences of Thanos' snap

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Apr 24, 2019, 11:30 AM EDT

It's been almost a year since Thanos landed a massive blow against The Avengers and all life in the universe in Avengers: Infinity War. The Mad Titan seized the Infinity stones and, with the snap of his fingers, utterly decimated life everywhere.

The consequences were tragic and heavily felt, leaving Earth's mightiest heroes and audiences feeling helpless and lost. The impact of the snap was easily felt as we watched these characters, some of whom we've spent a decade getting to know, blow away in the wind. It was personal, individual, real.

What's perhaps even more terrifying is the abstract, unquantifiable consequences to Earth's ecosystem on the whole.

With Marvel's Avengers: Endgame on the horizon, let's imagine what sort of world we might encounter when we return to our costumed comrades, in the wake of the worst ecological catastrophe in recorded history.

Extinction Level Event

The world has known five major extinction events in its history. Each of these has represented a massive loss of species planet-wide.

We've got a pretty good idea of what was behind the KT extinction that wiped out the dinosaurs 65 million years ago. But the precise cause of Earth's other major extinctions isn't totally known, though some scientists suspect drastic climate change to be at their root.

There is some suspicion within the scientific community that we are currently experiencing the sixth mass extinction event. Human-driven climate change has a serious impact on the global ecosystem and species are disappearing at a significantly higher rate than normal.

Problems like this are difficult to tackle because of the time spans involved. Humans are used to immediacy. We evolved to address the predator leaping down from the tree, an event spanning mere moments. Problems drawn out over decades or centuries are trickier.

This is, by some accounts, precisely the problem Thanos was attempting to solve. He imagined a world incapable of sustaining our continued growth. It was a scenario he'd seen before, on his own world. Thanos saw the Earth, and worlds everywhere, hurtling toward catastrophe unless someone — he — stopped it. Never mind that with the same snap of the fingers he could have doubled resources, wiped out the effects of climate change, or erected impenetrable walls around animal sanctuaries. Moreover, if saving or maintaining balance on Earth was truly Thanos' goal, wiping out half of all life was one of the worst ways he could have gone about it.

Half of All Life

In an interview with Birth Movies Death, Marvel Studios chief Kevin Feige confirmed that the snap didn't impact only human and humanoid populations, it also decimated plants and non-human(oid) animals. When asked about the ultimate fate of horses and ants, he said, "Yes! Yes. All life."

It seems an odd choice for someone who, ostensibly, is attempting to help us by hurting us. There is an argument to be made, albeit a horrible one, that halving the human population might have a positive impact on the planet as a whole. But that argument falls apart pretty quickly if you really stop to think about it, something Thanos clearly didn't do.

For one thing, human population growth is such that halving the population, while psychologically abhorrent, wouldn't do much to stem the tide in the long run. Global human population reached four billion people around 1974 and is estimated to hit eight billion in 2023, only 49 years later. Culling the population by half would do little more than traumatize us, make us angry, and knock us back roughly 50 years. Provided Thanos is right about our imminent demise at the hands of out-of-control population growth, unless he's willing to repeat the procedure every half-century, it's not a workable long-term solution.

More foolish still, Thanos takes out his vengeance on all life, not just sapients. That means half the trees, half the insects, half the elephants, and the dogs and the bacteria. And that's where his plan really falls to pieces. Because all things being equal, the decimation would even out, but all things aren't equal.

The Imbalance of Balance

It might seem, on the surface, as if reducing all life on Earth by half would be tragic but even-handed. That might be true if there weren't other considerations, but there are a lot of variables at play.

There is a sort of economics going on in biology and while a flat tax might seem like a fair thing to do, it burdens the lower brackets much more heavily. To explain, let's consider the humble bacteria.

There are varying estimates as to the total number of microbes living in and on your body right now but regardless, the number of microbes inside you outnumbers the number of cells that are you. They number in the trillions. In terms of sheer numbers, you're more microbe than human. But microbes are small, smaller even than the individual cells from which you are comprised. Estimates suggest they account for two to six pounds of the average human.

Calculating the total number of microbes on Earth is even harder to accomplish. But holy smokes there are a lot of them. It's believed that the number of individual bacteria worldwide is in excess of 10 to the 30th power. That's a one with thirty zeroes after it. To put that into perspective, the total biomass of bacteria is something like 3,000 times the biomass of humans. And half of it would disappear as soon as Thanos snapped his fingers.

One unforeseen consequence of the snap is that each of us would immediately lose roughly one to three pounds. Doctors hate him. See how Thanos trims the inches off your waist with one simple trick.

Don't feel too bad for the humble bacteria, though. They've got hard numbers on their side. Even those bacteria which live inside you, though a minuscule fraction of the whole, would be fine.

You might experience some gastric distress as your interior microbiome recalibrates but the doubling time of bacteria is measured in hours and would likely reach equilibrium again relatively quickly. In fact, you might suffer a heavier hit to your microbiome when undergoing a course of antibiotics. In the economics of biology, the bacteria is comfortable in the upper class. It might not like a 50 percent tax, but odds are it will weather the storm just fine.

On the other end of the spectrum, we have some of the most beloved animals Earth has to offer. If we continue our economics analogy, these are severely low-income. They have very little to spare and will suffer disproportionately at the hands of a fifty percent cut.

The Malayan Tiger has, at current estimates, between 250 and 340 individuals remaining. The Cross River Gorilla, only 200 to 300, and the Vaquita — a species of porpoise discovered in 1958 — only 30.

Cutting their populations in half would spell an almost certain death sentence to these already critically endangered species.

Thanos' decimation would impact all of us fiercely, as seen by the emotional reactions of our favorite heroes, but some life on Earth would never recover. For some, giving up half means giving up all.

Colonial Organisms

For a species such as ours, social yet fiercely individual, the loss of the one or the many does not necessarily mean the loss of the whole. While the evaporation of half our number would surely mean losing some of humanity's greatest thinkers, artists, and leaders, we would endure. But what about those species which are colonial in nature?

Consider the bizarre but beautiful Portuguese Man o' War. The Man o' War is a siphonophore, while it appears to be a single animal, it is actually a colony of many separate animals all working in concert. You can think of them as a complex organ system operating without the benefit of an enclosing skin.

The individual animals, known as zooids, are specialized, responsible for completing specific tasks in order to keep the colony healthy and functioning.

What would be the impact of the snap on a colony such as this? If half of their number fell to dust, could they regroup and carry on? Or would they discorporate and die without the cooperation of the whole? It's likely a great many of them, and other animals like them, would die. Probably more than the intended fifty percent. And what impact would the loss of such a species have on the greater oceanic ecosystem?

When it comes to ants or bees, the coin toss that is Thanos' finger snap might spell the end.

For a population which relies on a single individual for reproductive purposes, such an event could be catastrophic.

In bee hives, when a queen dies, there is an ordinary process of recovery. Workers will identify larvae of the appropriate age and begin the process of rearing a new queen. But this doesn't always work. If the colony does not succeed in rearing a new queen, it dies.

Statistically, in the moments after the snap, half of all bee colonies, the world over, would be without a queen. And some percentage of those would fail in raising a new one.

This problem would be exacerbated by the sudden disappearance of half of all the world's plants.

Will Somebody Please Think of the Trees

It's easy to consider the cost of the decimation to humans and other animals. But plants, while easily forgotten, might be the biggest threat of all to life on Earth.

So much of our global ecosystem depends on them. Not only do they perform a vital service in converting carbon dioxide into breathable oxygen, but they are the first step in the chain of converting the Sun's light into consumable calories.

While creature comforts are nice, there is a short list of things which are necessary for us to keep on milling around this planet, and plants are responsible for the really important ones: air and food.

Half the plant life on Earth means half the conversion of carbon dioxide to oxygen. There would be half the number of breathing animals, so it wouldn't be an immediate problem. But as we've already discussed, the doubling time of species varies. The various recoveries of stilted species would happen at different rates, throwing the balance of the planet's ecosystem wildly out of balance.

In the end, it's likely that Thanos' magic solution is anything but. His decimation would truly be a worldwide extinction event grander even than his imaginings.

It's probable that life on Earth would endure. It endured the Permian extinction which saw the loss of 96 percent of all species, but the world on the other side of the snap would be very different than the one we know.

Large animals like us would have the hardest time, while smaller ones with fewer survival requirements would see a boon. You can expect rat populations to explode after their initial recovery and they might even bring catastrophic diseases with them.

The loss of half of our loved ones would only be the first, and maybe the least, of our worries. But that purple disseminator of death would have worries of his own.

What Thanos didn't consider will be his true undoing, the collective ire of humanity at the unwarranted deaths of half our cats and dogs. Not even the Mad Titan is prepared for a planet full of 3.5 billion John Wicks.

Let's hope it all works itself out when Avengers: Endgame hits theaters this week.