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.

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Some people make much better neighbors than roommates.

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.

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"Jump. Dude, jump. MOTHERFUCKER, JUMP!"

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.

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Look at that asshole. Fuck that place.

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

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.

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It's why the scientific community refers to them as "astrenemas."

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.

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Thanks, fatass!

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.

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And they laughed every single time.

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.

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And so the world's first paparazzi was born.

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