1. In 1996, NASA researchers reported that a meteorite contained evidence that life once existed on Mars. But others argued that the evidence was most likely caused by inorganic processes that could be recreated artificially. A second group of NASA researchers (containing some scientists from the first study) has reexamined the 1996 findings using a new analysis technique called ion beam milling, and they again claim that living organisms are most likely responsible for the materials found in the meteorite.
The new study not only reexamined the contents of the meteorite itself, named ALH84001, but tested the alternative, non-biological hypothesis. "In this study, we interpret our results to suggest that the in situ inorganic hypotheses are inconsistent with the data, and thus infer that the biogenic hypothesis is still a viable explanation," says Kathie Thomas-Keprta, a senior scientist for Barrios Technology at Johnson Space Center in Houston
47 page pdf of the new analysis of the Mars "fossilized life" rock.
“The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade,” said McKay, NASA chief scientist for exploration and astrobiology, JSC. “This evidence includes signs of past surface water including remains of rivers, lakes and possibly oceans, signs of current water near or at the surface, water-derived deposits of clay minerals and carbonates in old terrain, and the recent release of methane into the Martian atmosphere, a finding that may have several explanations, including the presence of microbial life, the main source of methane on Earth."
2. "By being stuck at Troy [crater on Mars], Spirit [Mars Robotic Rover] has been able to teach us about the modern water cycle on Mars." Indeed, Spirit's saga at Troy has given scientists material evidence of past water on Mars on two time scales: ancient volcanic times, and cycles ongoing to the present day.