But as simple as the bacteria that formed stromatolites are, they were almost certainly not the very first life forms. Since these bacteria were "evolved" enough to have formed metabolic processes, scientists generally assume that they were preceded by some simpler, precursor life form. But between biological nothingness and bacteria, what was there?
Far from being the subject of armchair philosophy or wild speculation, investigating the origins of life is an active area of research and of interest to many scientists who, like Reader and Joyce, approach the questions experimentally.
Since the fossil record may not show us how life began, what scientists can do is to determine, in a general way, how life-like attributes can emerge within complex chemical systems. The goal is not necessarily to answer how life did emerge in our early, chemical world, but to discover how life does emerge in any chemical world--to ask not just what happens in the past, but what happens in general.
The most important questions are: What is feasible? What chemical systems have the capacity to display signs of life? What is the blueprint for making life in the chemical sense?
One of the great advances in the last few decades has been the notion that at one time life was ruled by RNA-based life--an "RNA world" in which RNA enzymes were the chief catalytic molecules and RNA nucleotides were the building blocks that stored genetic information.
"It's pretty clear that there was a time when life was based on RNA," says Joyce, "not just because it's feasible that RNA can be a gene and an enzyme and can evolve, but because we really think it happened historically."
However, RNA is probably not the initial molecule of life, because one of the four RNA bases--"C"--is chemically unstable. It readily degrade
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Contact: Keith McKeown
kmckeown@scripps.edu
858-784-8134
Scripps Research Institute
18-Dec-2002