He’s so worried that he thinks we have to get off Earth and grow into a multi-planet species as soon as possible, according to an article posted by blogger Tim Urban called How (and Why) SpaceX Will Colonize Mars. Musk’s thought is quite straightforward. Perhaps by the time the next huge asteroid heads our way, we’ll have the equipment to protect the planet or redirect the space rock. But if it’s something a bit more disastrous, like a neighboring star exploding, we may all get vaporized. 

Musk says we certainly can’t afford to just wait around and find out. In his article, Urban provides us another way to think about it: Visualize Earth as a hard drive, and every single species is a word document saved on that hard drive. The hard drive has already been crashed at least five times, and each time it misses a giant piece of those documents (species being vanished). So you can reflect the human species as an extremely valuable document generated on that hard drive: “Now—if you owned a hard drive with an extraordinarily important Excel doc on it, and you knew that the hard drive pretty reliably tended to crash every month or two, with the last crash happening five weeks ago—what’s the very obvious thing you’d do? You’d copy the document onto a second hard drive.”

That’s precisely why Musk is so hell-bent on Mars — it might turn out to be humanity’s backup drive.