The first organism able to substitute one of the six chemical elements crucial to life has been found. Until now, the idea has been that life on Earth must be composed of at least the six elements carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus - no example had ever been found that violates this golden rule of biochemistry. The bacteria were found as part of a hunt for life forms radically different from those we know.

This is a preview clip from the BBC Four documentary, 'Drake's Equation: The Search For Life', part of the 'Tools For Science' season.