The Search for Extraterrestrial Life: Are We All Martians?

NASA scientists recently announced they had discovered an organism that uses arsenic instead of phosphorus in its metabolism. The geologist Dirk Schulze-Makuch talked to SPIEGEL about the implications of the findings and the likelihood that life could exist on other planets.

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: 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 -- beggars can't be choosers. The arsenic bacteria are a wonderful example of the adaptability of microorganisms.

SPIEGEL: What does this discovery mean for the search for extraterrestrial life-forms?

Schulze-Makuch: The arsenic bacteria help us broaden our horizons. 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.