extreme impact in the last 1000 million years or so, blowing a large part of the surface of Mars into space. Not as unlikely as it sounds, with the asteroid belt neighbouring Mars and the denser asteroids mostly on the inside of it. What's been flowing there was lava and dust, not so much water. You don't need too believe me -- or any other single person for that matter. Just make up your own opinion from the facts. How would you explain away that the atmosphere of Mars is too thin and too cold for liquid water, and, judging by the relatively little change in earth's temperature over the last 3.9 billion years, probably was so during that whole time? How do you explain the difference in number of craters on the two sides, especially when water is unlikely to have caused it? February 7, 2012 at 8:49 am | addison Carl, earth loses part of it's atmosphere all the time. The reason Earth is not dead is that Earth has a molten core, Mars does not, therefore no magnetic field to protect it, and with volcanism, no replenishing the atmosphere with new gasses as constantly still happens on earth. February 7, 2012 at 9:13 am | Carl Addison, besides the answer I gave Aaron, the question is, how much is blown away every year. Afaik, Earth only looses a few tons in that time period. Even if it was a few thousand tons, that's nothing on a planetary