It’s strongly suspected that Mars was warmer and wetter in the past. It had to be above the freezing temperature of water at various times for the geological evidence uncovered by a suite of probes to make sense. But now we have the first hard estimate of just how warm ancient Mars may have been:

By analyzing carbonate minerals in a four-billion-year-old meteorite that originated near the surface of Mars, the scientists determined that the minerals formed at about 18 degrees Celsius (64 degrees Fahrenheit). “The thing that’s really cool is that 18 degrees is not particularly cold nor particularly hot,” says Woody Fischer, assistant professor of geobiology and coauthor of the paper, published online in the Proceedings of the National Academy of Sciences (PNAS) on October 3. “It’s kind of a remarkable result.”

If little Mars was a balmy 64 degrees in the Hadean Eon, presumably from the effects of outgassing and impacts, imagine how blistering hot it must have been on the much larger early earth? If you could have seen those ancient worlds, which one would you have bet on to turn into a dead wasteland vs. the future home of a vast ecosphere of trillions of species inhabiting land, sea, and sky?