There are 7.7 billion humans on Earth today. Here’s what would actually happen if Thanos destroyed 50% of all life on the planet.

In "Avengers: Infinity War," the villain, Thanos, achieves his ultimate goal: to wipe out 50% of all life in the universe.
Ethics aside, there’s a scientific reason for why Thanos’ plan won’t work the way he thinks.
Endangered species wouldn’t recover, setting off a chain reaction for a possible entire ecosystem collapse. So the quality of life for species that did survive would be terrible, at best.
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Following is a transcript of the video.

Narrator: As far as supervillains go, Thanos is, well, not very bright. Say what you will about Doc Oc, Syndrome, or Lex Luthor, at least they put considerable scientific thought behind their evil plans.

Doc Oc: "Nanowires feed directly into my cerebellum"

Meanwhile, check out Thanos’ master plan.

Gamora: "The entire time I knew Thanos, he only ever had one goal. To bring balance to the universe by wiping out half of all life."

Narrator: Yeaaaaah. This scheme to conserve resources by eliminating half of all life makes no sense. In fact, it wouldn’t save the planet. It would doom it. Let’s start with his decision to wipe out half of humanity. Now at first, you can see his reasoning. After all, there are 7.7 billion humans on the planet today. That’s nearly 7% of all the people who have ever lived in the history of our species. Which makes for a pretty crowded planet. So if half of us suddenly vanished … wouldn’t that be a worthy sacrifice?

No.

Ethics aside, we’d still be left with almost 3.9 billion people. About the same world population in 1972! So if history repeats itself, it would buy us less than 50 years before we reached current levels again. And the same is true for many animal species, like deer, who’s healthy populations would help them rebound quickly. But unfortunately, the same can’t be said for endangered species, who have the opposite problem.

Take the critically endangered Sumatran tiger, for example. Experts estimate there are fewer than 400 left on the planet. If half disappeared, there wouldn’t be enough to sustain the population, and they would likely go extinct. And endangered sharks, hawks, and leopards would probably meet the same fate. And that’s where Thanos’ plan to save the world REALLY falls apart. Because once a top predator disappears, they can take the rest of their ecosystem down with them.

Take gray wolves, for example. The US government eradicated them from Yellowstone in the 20th century. With the wolves gone, the elk population exploded and devoured the local vegetation, which disrupted the population of beavers, birds, and other species that relied on those plants to survive. And it gets even worse once you consider that half of every plant species on Earth is gone, too.

Because just like with animals, there are thousands of endangered plant species, many of which are too vulnerable to survive Thanos’ plot. And if plant species die out, the rest of their food chain would starve. Of course, many plant populations aren’t endangered.

But even that won’t save them all in the long run. You see, scientists estimate that 90% of all flowering plants depend on animals to reproduce. But Thanos wiped out half of all bees, fruit bats, and every other pollinator on the planet. Many of which are already in trouble. For example, 50% of bee species in the Midwest have vanished in the past century. And the lesser long-nosed bat, a key pollinator in the Sonoran Desert is also disappearing.

So they would probably die off completely. And if enough pollinators go poof. We’re looking at a possible total ecological collapse. So, while Thanos’ plan wouldn’t directly devastate thriving species, the chain reaction that could come from eliminating endangered species could really mess things up for everyone else left alive.

Nice going, Thanos. To be fair, the planet has experienced mass extinctions before, and life recovered. For example, an asteroid strike 66 million years ago wiped out 75% of all species on Earth. And with the dinosaurs out of the way, our mammalian ancestors flourished. But even so, experts estimate it takes around 20 million to 30 million years to recover from mass extinction. So unless waiting around for millennia was all part of his plan, the Mad Titan messed up, big time.