Scientists working to see if Mars ever had life have concentrated, of course, on looking for water. It appears to have been abundant on Mars a long time ago, but what was it like?
On Earth, water can be pure, or salty, or laden with minerals and metals. On Mars, the presence of minerals like jarosite indicate that at least in some spots, Martian water was high in minerals, with a corresponding high acidity. That's bad enough, but now evidence from the rover Opportunity indicates that the water was also very salty, far higher in salinity than Earth's oceans.
This has dimmed somewhat the idea of life on Mars, at least lately -- meaning, the last few billion years. It's possible that the water was in better shape to develop life as we know it early on in the history of Mars, but over time, the water got more acidic and more salty. At first blush, this precludes life arising and flourishing on the Red Planet, but I wonder. One scientist said "This tightens the noose on the possibility of life," but I think that's a hasty conclusion.
Life arose on Earth almost immediately after the asteroid and comet bombardment ceased, just a billion or so years after Earth formed. Conditions then were very different than they are now, and yet here we are. Whatever life started back then, it evolved, adapted. Every corner of the Earth has life in it, from miles down under the surface to pools of chemicals that would kill a human (and most bacteria) instantly. Check out D. radiodurans for a real eye-opener on how tough life can be. I have little doubt our oceans have changed their salinity numerous times over the past 3 billion years, and life adapted.
From this press release, it's impossible to say how much things have changed on Mars -- besides, of course, the loss of its atmosphere, its water, and the drop in temperature. In this case, I mean how the water on Mars changed over time, and how rapidly. If it happened overnight, then sure, it's not hard to imagine it wiping out all life on the planet. But what if it took, say, a few million years? Life on Earth has survived horrific circumstances in the past. Could any possible Martian life have done the same?
We still have no idea if life ever arose on Mars or not -- Mars cooled more rapidly than the Earth did, and so may have had life on it before we did. If any life did form there, it may not be around anymore, and there could be any number of causes. We simply don't know, and I think it's way too early in our exploration of the planet to rule anything out.