[ceejayoz]

40 years of probes haven't been testing for it. To my knowledge, the last formal attempt at actual detection of life (not conditions for life, but life) was the 1970s Viking landers. There's not even scientific agreement on the right way to search.

Meanwhile, here on Earth, we thought until recently that deep sea vents were sterile. If we didn't know life's limits here, we certainly can't claim to know them on Mars.