[SciShow intro] Hank Green: Do me a favor. Right now, picture in your mind the toughest animal on Earth, whatever you think it is, and now imagine what that animal would do in the most inhospitable environment that you could imagine. So, for example, if you thought of a grizzly bear on top of Mt. Everest being attacked by a swarm of silver-backed gorillas, you would be wrong, that is neither the toughest animal nor is it the most inhospitable environment, but I thank you for the visual image, that was a good one. Do you wanna know what the toughest animal on Earth is? Well, voila, there you have it. My friends, it is the tardigrade, also called a ‘water bear' or a ‘moss piglet', because they're plump and waddly and they like to suck on moss, and you may have noticed they're actually kind of cute. They're what scientists call ‘extremophiles', which means they don't give a crap about where they live. The tardigrades' secret is that when the environment gets too tough, they just shrivel up and die for a while, with the option of reviving when conditions improve. And that is the weird thing about tardigrades, they're so extravagantly tough. Like, for no real reason, they're supposed to like, waddle around on moss and suck up water, that's their job, and yet, in their dormant state, they can withstand temperatures close to absolute zero and up to 300 degrees Fahrenheit. They can survive being exposed to 1,000 times the radiation that would kill an elephant. They can withstand pressures up to six times what you find in the deepest oceans on Earth. What is the point of that. There's no place that that would be useful on Earth. And you had better believe that we have been sending these little waddlers into outer space, because what is the most inhospitable environment? Yes. It is space. In fact, scientists think that tardigrades may be the key to understanding how life began on Earth. Back in 2007, NASA put a bunch of tardigrades on the space shuttle. Then they opened up an air-locked door and left them outside in the vacuum of space for 10 days being exposed to crazy amounts of UV radiation. Then they brought them back to Earth, and when they got there, the tardigrades were like, what's up? They were happy and healthy and some of them lay tardigrade eggs and had little tardigrade babies that were completely normal. And we keep doing it. Earlier this year, in the very last mission of the space shuttle Endeavor, we sent some tardigrades up. The European Space Agency sent some tardigrades into space as part of a mission called Tardigrades in Space, uh, which isn't clever until you realize that they shortened it to TARDIS. So the question is, why do we keep shoving these adorable little beasts into the vacuum of space, it doesn't seem like a very nice thing to do? Well, one, because we want to understand how the tardigrades work, just scientifically, how they can possibly survive these intense horrible inhospitable environments. And two, because we're interested in proving the Panspermia hypothesis. That is right, Panspermia, a word I am not going to make a joke about. So imagine for a moment a meteorite slamming into our planet, and this meteorite is so large that it actually ejects pieces of the Earth into outer space. Now imagine on those pieces of earth that got ejected into outer space, there are tardigrades. If that little organism could survive the vacuum of space long enough to then fall down onto another planet, it could seed that planet with life. If life could be transmitted in that way, then it becomes much more likely that life is a very, very common thing in our universe. The Panspermia hypothesis has been around for a long time, but thanks to tardigrades, it's starting to look a lot more credible. So we can already thank these little beasts for being a great proof of concept for us, but of course, they will never know that we are so in their debt, they're just going to keep walking around on moss, sucking water off, and occasionally, visiting other planets. I'm Hank Green. That was today's SciShow dose, and we hope you learned something.