In 1996 Nasa held a press conference to announce they had found evidence of microscopic life in a martian meteorite known as ALH84001. They had found what looked like fossilised bacteria as well as organic chemicals similar to those found when bacteria decay. However many scientists remain unconvinced and the argument still rages about whether these patterns were the result of contamination or are in fact non-living mineral structures.
Just as in the 70s when NASA was a bit premature in announcing that the Viking Landers had found no evidence of life on Mars, in 1996 they were premature in announcing that the meteorite ALH84001 contained proof of bacterial life on Mars.
Both experiments remain inconclusive.
and
http://www.newscientist.com/article.ns?id=dn2283
The universe is a big place we are a fish bowl compared to the Ocean of the Universe.