Is life on earth a one-time event?

All elementary discussions I have seen assume a single origin, and show evidence consistent with it. However, the details of the origin of life are still unknown, so we can't say that there was not more than one origin.

http://www.americanscientist.org/issues/feature/2009/3/the-origin-of-life

 

It is, at its core, a probability argument. I suppose that it is possible to view the origin of life as chemical selection operating on different versions yet in the end, only one succeeded. It is worth noting that as far as we know, all life shares common polymers, Nucleic acids and protein catalysts. There are over 390 naturally occurring amino acids known, yet all living organisms consist of the same subset of 22 amino acids. There also seem to be some early indications that amino acids in this subset could be thermodynamically favored in prebiotic synthesis.

http://www.talkorigins.org/faqs/comdesc/section1.html#fundamental_unity
http://pandasthumb.org/archives/2009/04/ten-amino-acids.html

 

read upon this experiment
http://en.wikipedia.org/wiki/Miller-Urey_experiment#Chemistry_of_experiment.

I am sure that something similar is brewing up somewhere else in the universe.

 

Not necessarily. There is current active research looking for non-DNA-based microbial life here on Earth, assumedly left over from Earth's formative years. The idea that we've never seen evidence of it is that it would have slipped right through the cracks of all our current tests - whether that means not detected or merely not differentiated.