We believe it was Carl Sagan who said, "Every atom in your asshole was forged in the heart of a dying star." It's another way of saying that the life of the universe is one long story of things exploding and then re-forming into other things, only to explode later and have it all happen again.
So while we spend our lives worrying about some sort of Earth-shaking cataclysm like an asteroid strike or an earthquake, the truth is that we wouldn't be here without disasters even bigger than that. Life as we know it was only able to form because the universe likes to slap us around every few billion years. It's a form of tough love, we suppose.
For example ...
5A 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.
University of Copenhagen via Spacefellowship.com
And it was a dick.
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.
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?
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You can't see it, but there's a boombox orbiting the moon and blasting Peter Gabriel.
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.