So, I suppose the obvious theory is now that the asteroid belt is the remnants of a planet that was blown up, that Mars orbited it, an inhabitable moon, that a civilization lived on Mars, but had its atmosphere blown away by the blast. The Martians all came to earth to start new anew which is why we have no signs of early development leading up to civilization on Earth.
Simple really. Wouldn't it be amazing if someday research in our solar system might actually prove it?
If my survival could be guaranteed on Mars for 30 years, I would make the proposed one-way colony trip. Would you?