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Here is the article from Scientific American: http://www.sciam.com/article.cfm?id=are-aliens-among-us .

It dicussed what scientists generally qualify as "characteristics of life;" it's what we went over at the beginning of the year.

This article discusses scientists' search for "alien life" that arose seperately from what we commonly accept as life here on Earth. Apparently there has been a long-standing theory that life arose more than once on Earth, perhaps creating a completely different form of life from what exists today. (This might be the key to finding life on planets other than our own). Scientists are now looking in regions where conventional life would not be able to survive, areas where even extremophiles find the conditions a little uncomfortable. The hunt is on for microbes existing with right-handed amino acids and left-handed DNA, exotic amino acids that exist in no present life forms, microbes that use arsenic instead of phophorus, or silicon-based rather than carbon-based microscopic life. Finding any one of these proposed microbes would radically change view of evolution and life as according to science.

 It's interesting. And relevant to our conversation about cells, (in 1988, Olavi Kajander at the University of Kuopio in Finland observed ultrasmall particles inside of mammalian cells, as small as 50 nanometers, and proposed that they were living organisms that lived in urine and created kidney stones).

I'm not sure how much credibility his proposal has, but it creates an interesting hypothesis for our view of life.