5 Horrific Disasters That Made Human Life Possible

5 A Cataclysmic Impact Gave Us the Moon (Which Made Life Possible)

Even tiny meteors can make for some spectacular videos, and it doesn't take a very big one to wreck the Earth. So when you imagine an entire other planet slamming into us, well, you've got a disaster scenario they don't even bother making movies about. But it happened, a long time ago.

About 40 million years after the sun was born, the inner solar system became the scene of a turf war between giant piles of rocks. Just as baby Earth was figuring out how to poop in a toilet, a planetoid five times the size of fucking Mars slammed straight into us. That runaway planet even had a name -- Theia.

Once Theia hit the Earth, the shit hit the fan. The planet's iron core smacked us so hard that it eventually melded with our own core. Chunks of both planets catapulted into space. Yeah, Bruce Willis couldn't have saved us from that shit.

The Upside

Those orbiting chunks of Theia and Earth eventually made sweet love to each other and never got unglued. And that's how we got the moon. Some scientists speculate that it only took a month after the initial impact for the moon to come together. When it's right, it's right, you know?

And besides being pretty to look at and the source of our favorite werewolf lore, the moon's large mass is a huge part of why we're here today. For example, without it, we wouldn't have tides. As sea levels change, organisms are exposed to both water and air over a short period of time, forcing them to evolve and adapt. It could have been those changes that gave some animals the push to move from sea to land.

But the moon has another important effect: Its massive size stabilized the rotation speed and tilt of the Earth. Thanks to this, the overall climate of the planet has remained very diverse and incredibly stable over large periods of time, allowing life the necessary time to spread, evolve, and diversify and setting the stage for the rise of mammals and, eventually, us. All because of this random planetary collision that just so happened to create exactly the right chunk of debris.

4 The Iron Catastrophe Gave Us a Core

When scientists talk about the disastrous effects of "global warming," they're referring to a temperature rise of just a few degrees -- that's all it takes to throw everything completely out of whack. Droughts, floods, extreme weather -- all because things are on average just a little warmer than they are now. Yet there was a period in Earth's history when things got hot enough on the surface to melt fucking iron.

And once again, that hell-on-Earth scenario set the stage for people to arrive later.

You know that the Earth today has layers -- molten core, then rock, then the nice cool surface we live on, with flowing water and green jungles and such. But in the early days, it wasn't like that: It was one big solid mass with elements distributed throughout. After 500 million years, everything started to heat up. Pretty soon the evenly distributed iron and nickel melted and started flowing. As you know, gravity has this adorable way of drawing the heaviest elements toward itself -- it's like the local Walmart in that respect. The heavy stuff sank to the core of the Earth, setting everything else on liquid fire as it moved. For half a billion years, everything -- the surface, the core, the middle bits -- was hot magma. It was kind of like the irritating "lava level" every video game has.

The Upside

While the heavy elements like iron and nickel were sinking to the core of the Earth, the lighter ones like silicon and oxygen were forced to the surface. Usually we're not fans of segregation based on lightness, but in this case, things kind of worked out for us. Once everything cooled down, we ended up with a nice airy crust, a medium-density mantle, a liquid metal outer core, and a solid, spinning inner core that is as hot as the sun.

So that's one benefit. The other is that this hell of an epoch created a giant spinning ball of iron that generates a powerful magnetic force field around the entire planet. This force field deflects solar winds and all kinds of other space radiation away from the Earth. Without it, our atmosphere would slowly be blown away, turning our environment cold and dead, like Mars.

All of that changed due to this nightmarish phenomenon scientists awesomely refer to as "the iron catastrophe."

3 Our Oceans May Be the Result of Massive Comet Strikes

Go outside and look at the moon. Even with the naked eye, on a clear night you can see that it's absolutely covered with craters caused by projectiles that have been punching the shit out of it for millions of years. What you may not realize is that, while our planet has enough tectonic activity to cover up our biggest scars, it has taken just as much abuse. And it's a good thing, too -- the Earth might be completely dry otherwise.

Scientists theorize that the orbits of the planets shifted about 4 billion years ago, creating a gravitational kick that pushed Neptune outward, smashing it into the ring of comets surrounding our solar system. Millions of comets were scattered in all directions, literally bombarding Earth, Mercury, Venus, and Mars nonstop for about 100 million years. They call this the Late Heavy Bombardment, and it was kind of like Deep Impact times a thousand.

The Upside

There's evidence that points to our run-ins with comets and asteroids as a source of water on Earth. Specifically, scientists have discovered a water-carrying comet that originated from the exact same belt that beat the crap out of us 4 billion years ago. Comets are, after all, just dirty snowballs, so the idea is that if your planet gets hit with enough of them, soon it'll be covered in oceans. And by "soon" we mean in tens of millions of years.

But, like everything else in history that we didn't see with our own eyes, not everyone is convinced that the Great Beat-Up Session was how we got water. Even if not, we can still thank the Late Heavy Bombardment for our existence, because Jupiter redeemed itself by becoming our personal bodyguard. After knocking Neptune around, Jupiter took a new position in the middle of our solar system. So for the last few billion years, we've had a big fat gas giant blocking our path from would-be planet killers.

2 The Great Oxygenation Event Gave Us Air

Since we breathe oxygen, it's hard to think of the oxygenation of the planet as a disaster. But it was -- the Great Oxygenation Event almost killed off all life before it even got started.

Sometime around 2.4 billion years ago, the planet's atmosphere was as noxious as a truck stop Port-A-Potty. And anaerobic organisms like the ancestors of blue-green algae loved that poisonous, shitty air. They thrived on it. They ate it up and farted out oxygen as their waste product.

And for a while, this was a strictly bacterial world, because who else can live on poison and oxygen farts? Even the oxygen farts got gobbled up by iron deposits, creating rust-filled oxygen sinks that were no good to anyone. Then something crazy happened -- one of these stupid bacteria figured out "Oh shit, the sun!" and started using the process of photosynthesis to stay alive. Some scientists think that bacteria got so good at their job that their oxygen waste products ran out of room and started accumulating in the atmosphere. If you thought the dinosaur extinction was bad, you're right. We loved those guys. But the sudden influx of what was then a toxic element was bad, too, because it killed off just about every single living thing on the planet. It wouldn't be the first time we almost farted ourselves out of existence.

The Upside

While most organisms at the time couldn't survive swimming in a sea of their own filth, others figured things out by detoxifying the space around them or clustering together to stay alive. Boom -- complex organisms, baby! It took a few million years, but still. We couldn't have done it with all that methane in the air.

But that would hardly be the last time that a horrific, disastrous calamity would force life to get its act together ...

1 The Snowball Earth Got Complex Life Forms Rolling

As bad as global warming would be, it's nothing compared to what we would face if we were hit with a new ice age. About 650 million years ago, the planet entered the worst ice age in its entire history due to what scientists call the "fuck if we know" theory. (Although some suspect it might have had something to do with the previously mentioned oxygenation event that converted the atmosphere's methane into carbon dioxide.) As the temperature dropped, massive glaciers started to cover the planet, creeping slowly from the poles like mildew covering a rotting fruit.

Evidence suggests that the entire planet was covered in a thick sheet of ice for several million years, and the average temperature of the globe during that time might have plunged as low as -50 degrees Celsius. This planetary deep freeze happened at least three times.

If it sounds like nothing should have been able to survive that, you're right. But once again, life found a way.

The Upside

The fossil record tells us that complex animals started popping up about 650 million years ago, around the same time a sheet of ice covered the planet. Some researchers think that all those moving glaciers would have knocked the continents around, dumping large amounts of nutrients into the oceans trapped under the ice. While isolated, the earliest organisms used the influx of nutrients to get stronger, pruning out their weakest lines and rebuilding their genetic makeup. In the face of imminent death, they might have banded together and specialized functions in order to increase their chances of survival, inventing new features and creating the first diversity in early multicellular organisms.

In other words, they got smarter, because they had to.

Once the Earth thawed, life was free to build upon the survival abilities it learned during the ice age and get out of the ocean and colonize the land. This directly led to what is called the Cambrian Explosion, the greatest outburst of life (lifesplosion?), diversity, and complexity in the history of our planet.

But Earth had to turn into an inhospitable, frozen wasteland first. This would set the stage for what would become a running theme in our world: One species' disaster is another's savior.

Sebastien Paquin is a freelance writer and author of the longest and most ridiculous John Dies at the End fan fiction to ever lurk in the darkest corner of the Internet.

For more cataclysmic events that could destroy us, check out 5 Ways The World Could End (You'd Never See Coming) and 5 Cosmic Events That Could Kill You Before Lunch.