Scientists are saying rock analyses by the Mars rover, Curiosity, indicate that Mars may have supported microbial life. Moreover, they are saying Curiosity has ascertained that the nature of the water determined to have existed on Mars may have been benign enough to drink. Per the article:
The first analysis of powder samples drilled out from the inside of once water-soaked rock shows Mars was a suitable place for microbial life to evolve, scientists with NASA’s Mars rover Curiosity mission said Tuesday. Among the chemicals discovered inside the rock, called “John Klein,” were sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon, all key ingredients for life. The analysis showed that water which once soaked the rock had a neutral pH – not too acidic and not too salty...“We have found a habitable environment that is so benign and supportive of life that probably if this water was around and you had been on the planet, you would have been able to drink it,” Grotzinger told reporters...
I don't understand the excitement over this. So what? The kind of life Mars might have supported was certainly rather primitive. We know that the Martian atmosphere was much thicker some billions of years ago, and so yes, it may well be that some single-celled life formed on Mars. But a quick comparison with Earth does not bode well for the hypothesis that life formed on Mars. Remember, Mars receives about half as much sunlight per unit area that earth receives; with half the negentropy, a rough rule of thumb would suggest that life should develop at half the speed it did on earth.
The best guess now is that single-celled life took at least several hundred million years to appear, and eukaryotes took maybe two billion. The best guess for multi-cellular creatures first appearing is between one and two billion years ago.
Thus, multi-cellular creatures took at least two billion years to develop on earth; on Mars, they would have taken four billion -- not enough time. Therefore, the most optimistic guess is that we might find advanced single-celled creatures, but I think it more likely that we're talking about very primitive bacteria.
If so, it would be very interesting to see how similar their biochemistry is to ours, but I doubt that we'll ever find anything that will resolve that question; we certainly don't have any data of that nature for early life on earth.