I was watching the NOVA show about the mars landers, and I wonder if any of the photographs have shown shells, fossiles, etc., or any signs of previous life. If I’m not wrong, some of the rocks are definately sedimentary in origin, so presumably there might be the fossilized remains of ancient martian organisms in them. One photo i saw seemed to show shell-like impressions…has NASA seen anything that look like earth-type fossils? 
Not unless the Starbucks it rolled into counts.
Shell impressions on Mars? Goodness, no.
There only possible fossilized Martian life ever discovered was found in Martian rocks picked up here on earth. These “fossils” are purported to be Martian microbes and are very controversial.
Their primary purpose was to prove (or disprove) that Mars once had voluminous water. They’ve succeeded; it did.
Reading a bit between the lines of the link below I would say no, life has not been found on Mars. I am pretty sure we all would have heard of it if it had and a quick Google found the link below which talks about better ways to search for life on Mars (or former life anyway). One would suppose the arc of the story would be far different if evidence of life had been found.
If one of the landers did detect signs of life, even shell prints or microbes, I really don’t think it’d be possible to NOT hear about it. I don’t think you’d have to ask.
I think that we can all agree that such a discovery would rank as one of the most important discoveries of all time, right? Not necessarily in terms of usefulness, but rather implication.
At the moment, we are alone.
No, Opportunity photographed a few odd shapes in the rocks:
Tube worms on Mars?
More “segmentations”
But so far nothing that screams FOSSIL!
Have any of the landers carried microphones? has anyone heard the sound of martian winds?
Didn’t Calvin and Hobbes make faces at it? Oh, wait, that was the old Viking spacecraft… 
Zev Steinhardt
The Mars Polar Lander (1999) carried a microphone, but the probe disappeared after hitting the martian atmosphere.
Not the lander, and not fossils, but this article from Scientific American says that some scientists have detected enough methane in the Martian atmosphere to make a biological source possible, though still far from definite.
No life signs yet. Lots of signs that water was once plentiful.
Signs of life, as I understand it, will not come from shells or a footprint in the dust. Rather they will come in such things as discovery of the chemical byproducts of the metabolism of living organisms, like bacteria, and other stuff of that sort.
“We’d have heard about if they did.”
Well, I hate to bring this up, because it deserves more technical discussion that I have time to offer, but we’ve had such evidence as far back as the Viking landers of the 1970s – and indeed, long before that.
Viking carried 4 separate “life detection experiments” and the pre-launch protocol was clear: a positive result on any one of them would count as “finding [evidence of] life in the martian soil sample”. IIRC, one test was fully positive, one was weakly positive, and evidence from a separate geophysical experiement suggested biochemical evidence of life as well. These results were well publicized at the time, but NASA chose to declare the overall findings “negative” – and back then, in the shadow of Apollo, no one had much standing to argue with them.
NASA officially blamed the positive results on “unique soil chemistry.” Today, after almost 30 years, there is no one single plausible model for what that “unique soil chemistry” might be – it’s just hand waving. A few theories have been proposed, but all have been shot down as impossible.
Dr. Gilbert Levin, president and CEO of Biospherics [designer/builder of some of the Viking equipment] has told many colleagues over the years about how he was threatened by NASA managers (afraid that declaring a [possibly false] positive might make NASA look foolish) from the moment the first telemetry results came in from those experiments. Finally, he released his findings and analyses at an invited talk at the Annual Meeting of the International Society for Optical Engineering on July 30, 1997
But frankly, if you want evidence that there has been life on Mars, you need look no farther than the oxygen content of the atmosphere. Free Atmospheric Oxygen on Earth is the result of microbial activity (this highly reactive gas was once a dangerous waste product, and is still toxic to many/most microbial species; indeed, oxygen radicals are the first weapon of many of our own defensive cells) The “consensus” theory – that Mars oxygen is left from the UV dissociation of water, where the hydrogen diffuesed to the upper atmosphere and then into space-- has been powerfully criticized in many analyses, and seems contradicted by amoung of readily oxidizable substrates remaining in the soil and atmosphere.
The standard answer to the question: “Could we detect life on Earth from outer space?” has long been "Yes – with our oxygen atmophere being the most glaring evidence. Oddly, no one wants to come out and say the same about Mars. IMHO, it’s not the only case where theories have been orphaned or ignored for “comfort”
I don’t mean to offend anyone, or come off as a kook, but I think today’s public knows enough about NASA’s internal culture, going back to the early days of shuttle design (around the time of Viking) to see how they would rather “play it safe” rather than risk embarrassment. In fact, history has shown that, for many people involved in NASA projects from contractor technicians to the highest career NASA officials, “safe” actually means “avoiding embarrassment”, not “reducing risk to the spacecraft or crews”
There was only one Starbucks. (In itself suspect, with regards any current life) It was also entirely empty of Martians at only an hour after sunrise. Obviously, there is no life on Mars.
Tris
“We better get back, cause it’ll be dark soon, and they mostly come at night, mostly.” ~ Newt, Aliens ~
Orrrrrr----
It simply proves that the Martians have good taste, why doesn’t it?
Or they prefer tea, perhaps it does?