As far as we're aware of, the crust of Mars is even more sterile.

I'm pretty sure humanity currently possesses the knowledge and resources to build multiple underground shelters around the Earth (as seen in Hollywood movies) that can sustain a population of at least one million indefinitely. Food can be grown with artificial lighting. Air and water can be brought in from outside, purified and recycled. If you need anything else, send robots (or people in protective suits) to scavenge the surface. The only thing we lack is political will.