Are the aliens already here?
November 29th 2007 09:16
In this fascinating article in Scientific American, the physicist and cosmologist Paul Davies - who has a keen interest in exobiology - talks about the prospects and issues pertaining to the search for alien life right here on Earth. Such life is likely to be microbial, and would be detected by finding some key feature that would at the very least give us reason to suspect that the life form had a separate origin of life and evolved independently from the bacteria, archaea and eukaryota (the three "domains" of life on Earth).
Here's an excerpt:
"Another important variable is size. All known organisms manufacture proteins from amino acids using large molecular machines called ribosomes, which link the amino acids together. The need to accommodate ribosomes requires that all autonomous organisms on our tree of life must be at least a few hundred nanometers (billionths of a meter) across. Viruses are much smaller—as tiny as 20 nanometers wide—but these agents are not autonomous organisms because they cannot reproduce without the help of the cells they infect. Because of this dependence, viruses cannot be considered an alternative form of life, nor is there any evidence that they stem from an independent origin. But over the years several scientists have claimed that the biosphere is teeming with cells that are too small to accommodate ribosomes. In 1990 Robert Folk of the University of Texas at Austin drew attention to tiny spheroidal and ovoid objects in sedimentary rocks found in hot springs in Viterbo, Italy. Folk proposed that the objects were fossilized “nannobacteria” (a spelling he preferred), the calcified remains of organisms as small as 30 nanometers across. More recently, Philippa Uwins of the University of Queensland has discovered similar structures in rock samples from a deep-ocean borehole off the coast of Western Australia. If these structures indeed arise from biological processes—and many scientists hotly dispute this contention—they may be evidence of alternative life-forms that do not use ribosomes to assemble their proteins and that thus evade the lower size limit that applies to known life."
Continue reading here. Fascinating stuff!
Here's an excerpt:
"Another important variable is size. All known organisms manufacture proteins from amino acids using large molecular machines called ribosomes, which link the amino acids together. The need to accommodate ribosomes requires that all autonomous organisms on our tree of life must be at least a few hundred nanometers (billionths of a meter) across. Viruses are much smaller—as tiny as 20 nanometers wide—but these agents are not autonomous organisms because they cannot reproduce without the help of the cells they infect. Because of this dependence, viruses cannot be considered an alternative form of life, nor is there any evidence that they stem from an independent origin. But over the years several scientists have claimed that the biosphere is teeming with cells that are too small to accommodate ribosomes. In 1990 Robert Folk of the University of Texas at Austin drew attention to tiny spheroidal and ovoid objects in sedimentary rocks found in hot springs in Viterbo, Italy. Folk proposed that the objects were fossilized “nannobacteria” (a spelling he preferred), the calcified remains of organisms as small as 30 nanometers across. More recently, Philippa Uwins of the University of Queensland has discovered similar structures in rock samples from a deep-ocean borehole off the coast of Western Australia. If these structures indeed arise from biological processes—and many scientists hotly dispute this contention—they may be evidence of alternative life-forms that do not use ribosomes to assemble their proteins and that thus evade the lower size limit that applies to known life."
Continue reading here. Fascinating stuff!
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Comment by James Rickard
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