Riding on the answer to the question is the current hegemony of Darwinian evolution. If the primitive one-cell organisms (prokaryotes) self-assemble from inorganic materials, given the proper environment, natural selection, and a sufficient amount of time, and if all multicellular organisms (eukaryotes) evolve in turn from them by the same mechanisms, then the question boils down to whether there is anything particular or different about Earth's environment to suggest that life could have "evolved" only on this planet. Given that the universe is some 14.7 billion years old, and that the Earth is only about 4.5 billion years old, with the fossils of the first prokaryotes dating to about 3.7 billion years ago, there would seem to be no reason why the scenario that science assumes took place on Earth should not have been repeated many times over elsewhere in the universe.
In today's TED talk, astronomer Dimitar Sasselov explains how science is addressing the problem of life's origin from two different directions. On the one side, the recently launched Kepler telescope is supplying data on multiple Earth-like candidates which can be detected in rotation around distant suns. With such a rich list of candidates, astronomers are using the full range of their techniques to determine such parameters as atmospheric composition, size, mass, distance from the parent star, the presence of water, and so forth, in order to establish just how probable it is that other Earth-like environments exist in which life as we know it could flourish. Should they find any evidence of organic compounds, or other telltale markers for life, the Darwinians believe that their hypothesis of methodological naturalism would become more probable. (Logically, of course, no such conclusion would follow. If Kepler demonstrates that there are 100 other life-bearing planets out there, or 10,000, such an observation would still be consistent with life originating through someone's intelligent design. It just would mean that the designers have been somewhat busy in the past fifteen billion years, that's all.)
On the other side, astrobiologists and biochemists are combining their investigative resources to try to model a stable chemical pathway for the evolution of life from inanimate matter. As I discussed in this earlier post, they have their work cut out for them, because the evidence to date does not support that the intermediate molecular assemblies which they envision would remain stable enough in the primitive Earth's environment to allow them to form stepping stones to the next stage of evolution. We can show the spontaneous formation of organic molecules in a simulated environment, but the more complex they become through combination, the more susceptible they are to being broken down rather quickly by outside environmental factors.
Professor Sasselov is the head of Harvard's Origins of Life Initiative, in which the disciplines of astronomy, biology and molecular chemistry come together to try to solve the riddle of life's origin. Although I find science's current dismissal of intelligent design as an explanation for how life began rather amusing, given that the biogenetic code carries not only complexity, but also information, and given that the only known source of information to date in the universe is intelligence, I am willing to listen to and study all the mechanisms for spontaneous and random assembly which scientists trot out from time to time as explanations for what might have happened. It is rather like physicists investigating all the colors and ink molecules in a Calvin and Hobbes comic strip, and positing how this color has an affinity for this one, while this size ink molecule attracts others of this size -- and so forth and so on, to explain how such a phenomenon "spontaneously" came into existence over time, without any need for Bill Watterson.
Thus as you watch Prof. Sasselov's talk below, keep in mind that the "bridge" he envisions being joined from both sides may well have hard data from the astronomical side, with more to come as Kepler downloads its observations. But the data thus far from the other side -- the biomolecular data -- is still nothing more than computer simulations and fancy programming, which themselves are the product of scientists' intelligent designs (i.e., knowing in advance what they are seeking -- unlike "blind" nature itself):
There is more about Professor Sasselov on this page; and here is a link to the Origins of Life Initiative, where you can read much, much more about the current research they are undertaking. Watch this talk in its high-res version from this link, and download it in that and other formats from this page.