Is life in the universe as common as the stars in the sky?
… if mankind does not destroy itself on-time… we might even find out.
Why Mars?
So why Mars? Mark (and fortunately lots of other people) believe that Mars is the best place to go to answer the Big Question: Is life on Earth a bizarre cosmic accident, or is life a natural consequence of the way things work in the universe, as common as the stars in the sky? One way to answer the question positively is to find a nearby example of life that developed independently of life on Earth. That would cinch the case that life is almost inevitable, given the right conditions. The recent discoveries of planets around other stars assures us that planets themselves are not accidental or even rare, so that the right conditions must be out there. So if we found clear evidence that life developed independently on Mars, even if it’s not there today, then we’d know there must be other places out there, lots of them, where life developed and flourished as it did on Earth. And so there might be life out there somewhere asking itself the same questions … Mars is a good bet to find this evidence because we know that, unlike today, Mars was warm and wet at the same time that life made its first appearance on the warm, wet Earth, about 3.8 to 3.5 billion years ago. Furthermore, this appearance of life on Earth came almost immediately (in a geological sense) after the heavy bombardment of space rocks ended which, while it continued, made the Earth’s surface a rather inhospitable environment for what we imagine as fledgling life. In other words as soon as life had a chance on Earth, pow, there it was. So if Mars had similar conditions then, why not there as well? Why not indeed. 
So how do we find this evidence? There are two approaches. First, we could look for evidence of life from the time of its first appearance, as we have found on Earth. This could be difficult, but if life survived only a short time thereafter until Mars became cold and frigid, then it may be our only choice. Fortunately Mars has made this easier to do there than it is here on Earth by preserving large areas of ancient Martian terrain. This terrain has been relatively undisturbed since those ancient times–no weathering has rearranged, mixed up, and buried material there as it does here on Earth. The second approach is to assume that if life got started at all, then it has found a way, somehow, to adapt to the changing Martian environment and lives today. The trick there is that it may live today kilometers beneath the surface in underground water reservoirs where the heat from the planet keeps the water from freezing and the rock above keeps the water from being lost to space. So getting to that life would be rather tricky, but may be possible if we can find places where the water escapes to the surface in geysers, or at least gets close enough to the surface that we could realistically drill for it. Since there’s a lot of exposed ancient terrain with places where meteor impacts have done some digging for us, and since that’s when life started on Earth in similar conditions, we will probably go look for the ancient fossil life first. Of course there is the recently uncovered possible evidence of life in a Martian meteorite from that ancient era, and so if that evidence stands the test of scientific scrutiny then it is another compelling reason to start our search by looking for fossil life. Later we will probably try looking for any existing life, if we can find promising sites and the ability to get to (or have delivered to us for free) subsurface liquid water. In either case, we will be bringing carefully selected samples from Mars back to Earth so that we can apply our full arsenal of scientific equipment to the problem, and so that we can methodically rule out non-biological explanations for the observations without having to send an expensive mission to Mars everytime a new scientific objection is raised. One interesting risk of betting on Mars is that while life may have developed there, it may not have been independent of the development of life on Earth. We already know that Earth and Mars have exchanged material in the past, and so it is possible that life developed on one planet and then seeded the other. In fact Mars may have become hospitable before Earth, so perhaps life first evolved on Mars, seeded Earth, and we are the Martians! Now wouldn’t that be interesting … Lots of questions. Not a lot of answers. Let’s get to it. (Sorry, Mark thinks that that sort of stuff is a lot more interesting than Mark–now back to Mark.)
source: http://alumnus.caltech.edu/~madler/
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