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Permalink Reply by Chris Crawford on March 13, 2013 at 1:36pm

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.