I’m still digging through this epic WBW post but had to share this video that’s linked from the part about ‘how (and Why) SpaceX Will Colonize Mars’. From the video caption:
Learn what would happen if an asteroid hit the Earth with this detailed “Large Asteroid Impact Simulation”. An asteroid with a diameter of 500 km. Destination: The Pacific Ocean. The impact peels the 10 km crust off the surface. The shockwave travels at hypersonic speeds. Debris is blasted across into low Earth orbit, and returns to destroy the surface of the Earth. The firestorm encircles the Earth, vaporizing all life in its way. Within one day, the surface of the Earth is uninhabitable. The evidence shows that this has happened at least six times in Earth’s history.
That last bit, about previous events like this is something I didn’t know. From the WBW post I’ve learned there have actually been 5 mass extension events in the Earth’s past. The Dinosaurs were just the last. And we’re sort of coming due for the next. The idea goes then, that we’d better try and back up humanity on another planet and be ready for the asteroid (hard drive) to crash.