Inconvenient truth.
So if it happened on Mars, why didn't it happen on Earth back when it happened there? Earth is much closer to the Sun, and receives a much greater share of the same solar wind, so we must have been hit by a greater flux. And why didn't the solar wind dissociate the water in the Martian atmosphere into H2 and O2, and the latter reacted under the radiation exposure to form ozone (O3)which acted to shield the surface from further radiation? That's what happened on Earth. So why didn't it work on Mars?
I have an alternative theory. The ancient inhabitants of Mars built nuclear reactors, and the excess radioactive particles heated up the atmosphere causing global warming. 8)