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. "Our fixation with the idea that oxygen is essential to life is already short-sighted. This aggressive element inflicts damage to our cells in the form of free radicals. Maybe organisms elsewhere in space have found a gentler alternative. When we send space probes to other worlds, we should expect the unexpected."