Research to be presented tomorrow at the Goldschmidt conference on geochemistry is drawing an unusual conclusion: that all life on Earth originated on Mars. Professor Steven Benner will argue to his peers that the chemical conditions necessary for the development of life on Earth simply weren't present on Earth at the time we know life arose. This is a lofty claim - should we believe it?
Benner's argument centers around a rare element, molybdenum, which he believes was vital to life's early steps. For molybdenum to be effective, however, it would have needed to be oxidized - combined with oxygen atoms. The problem? There wasn't much oxygen on the Earth billions of years ago. Mars, on the other hand, had plenty. Mars also happens to be older than the Earth, giving life a chance to grow before conditions were ripe on our planet. So, perhaps the most basic life arose on Mars before travelling to Earth aboard a meteorite. Many of our meteorites originate from Mars, so that wouldn't be the most far-fetched of travel plans.
But missions since NASA's Viking landers in the 1970s have been searching for life. Wouldn't we have found it by now if it was numerous enough to get picked up on a meteorite? Probably not - tiny microbial life might not fossilize reliably. And even if it did survive, we've searched a truly minuscule portion of Mars. Imagine walking into the Sahara desert and picking up a handful of sand: how likely would you be to find a dinosaur? Not very!
None of this, of course, is evidence in favor of a Martian origin. To me it seems for less probable that life arose on Mars, survived years in space, and then found a hospitable Earth than that a little oxygen found a little molybdenum here on our planet and life took off. Just because this seems more likely, however, doesn't mean it's how things actually happened. He's the expert, not me!
And what if we do find evidence of Earth-like life on Mars? Would that be proof of our extraterrestrial origin? Sadly not. Contamination from Earth is a major concern when sending spacecraft to other worlds and, although we do our best, evidence suggests that Earth-born microbes may already have spread.