'Are We All Martians?'DER SPIEGEL: NASA scientists have discovered strange bacteria in California's Mono Lake. The microbes incorporate arsenic, which is usually poisonous for life forms, into their cells. Are they originally from another planet?
Dirk Schulze-Makuch [Geologist, Washington State University]: No, that can be ruled out. The arsenic bacteria also did not arise independently from the other organisms on Earth. Like all microbes, they multiply best when there is enough phosphorus around. They only use arsenic when there is not sufficient phosphorus...
SPIEGEL: What does this discovery mean for the search for extraterrestrial life-forms?
Schulze-Makuch: ... If we can find such exotic organisms on Earth, what strange beings could exist on other planets? We have to free ourselves from the idea that life-forms will resemble what we know from Earth... When we send space probes to other worlds, we should expect the unexpected. Life can appear anywhere: in poisonous seas or in hot clouds.
SPIEGEL: Where could the resistant arsenic bacteria thrive?
Schulze-Makuch: Arsenic-eating microbes would probably feel very at home on our neighboring planet, Mars. Its conditions are well suited to them... However, it could be that any life-forms on Mars aren't actually aliens, but are related to us...
Almost 4 billion years ago, Mars was a planet well suited to sustaining life, with massive rivers and lakes. Back then, the first primitive organisms appeared on Earth. These single-cell life-forms probably made it to our neighboring planet Mars by way of meteorites and established themselves there. It is possible that descendants of these primitive bacteria could have survived in nooks and crannies on Mars until today. Equally fascinating is the opposite possibility: Life could have started on Mars and then, via a meteorite, made its way to Earth. That would raise the question: Are we all Martians?
