Viking Labeled Release life experiment
From NewMarsWiki
Although the Viking Labeled Release life detection experiment that was part of Viking's science payload officially didn't find evidence of life, in 1997, Biospherics' President and CEO, Dr. Gilbert V. Levin, announced his new conclusion that his experiment found living microorganisms in the soil of Mars. Dr. Levin is convinced that the only possibility fitting all the relevant data is that microbial life exists in the top layer of the Martian surface.
