“For Mars to ever have been warm enough to make that possible, the Earth would have been turned into a piece of charcoal.”
No, that is nonsense. Mars had a much thicker and denser atmosphere, something like 99 percent Carbon dioxide. The weak gravitational force of Mars and absence of a strong and protective magnetic field resulted in most of that thick atmosphere and its hydrosphere to mostly be stripped off by the Solar Wind. The ancient hydrosphere and atmosphere made it possible to keep Mars a wetter and warmer place until they were lost to outer space.
Thank you. I was about to post something similar, you saved me the trouble.