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Microfossils

11layersS.jpg I mentioned about the evidence in terms of the fossil record for early life. What might this tell us about the origin of life? Here are examples of microbial fossils that I found in rocks 3.5 billion years ago from western Australia. The bar scales are ten micrometers. As you can see, there are the thread-like structures and indeed this one here, there's actually some partition and they're actually quite large. They're under ten micrometers in diameter so two or three micrometers would be this tubular structure here and this one approaches six or seven micrometers in diameter and many tens of micrometers in length. These are three dimensionally preserved in the rock. They are tubular also, this one is. As you focus up and down with the microscope you can get a three dimensional picture of this. So they're three dimensionally preserved in the rock, they are composed of organic material and the organic material in the rock associated with these microfossils show that the organic material is enriched in the lighter isotope of carbon, carbon-12. carbon-12 and carbon-13 are two stable isotopes of carbon. So CO2 that we have out in the atmosphere has two flavors. I'm leaving out carbon-14, the radioactive isotope of carbon.

When your green plant outside your window photosynthesize kinetically, the carbon-12 flavor of CO2 is preferentially utilized in photosynthesis so there's a fractionation. The organic material of the plant is enriched with carbon-12, compared to the reservoir of carbon dioxide, the carbon-12/carbon-13 ratio in the atmosphere. We can use that kind of information to suggest carbon fixation, photosynthesis in the rock record. The organic material with these fossils, is consistent with photosynthesis. The shape, the size of these microfossils, as well as other associated fossils, suggest that these are the remains of Cyanobacteria, the remains of oxygen releasing phototrophs, 3.5 billion years ago.

Now we go to the fun stuff. What does that mean with regard to the origin of life? What does that mean with regard to early microbial evolution? Microbiologists, molecular biologists, based on a variety of information, have concluded that Cyanobacteria were one of the last major groups of bacteria to have evolved. So there's sort of a more recent kid on the block within the prokaryotic world. Therefore, that would suggest that much of microbial evolution at the phylum or division level, major metabolic pathways, may have already been around by 3.5 billion years and that much of microbial evolution since that time was basically fine tuning on already well established biochemical pathways, metabolic pathways. So in a sense, what Jere Lipps might be saying, the large game was already over 3.5 billions years ago for prokaryotes and probably for animals, the major game on ground plans was over by the end of the early Cambrian. Interesting comparisons between the two and yet they're both telling us something very interesting.

Now, what about the rates of evolution? Does this tell us something there? Well, from the origin of life, remember we're not sure when it originated. If life, the last common ancestor occurred 3.8 billion years ago, then that leaves 300 million years from that first cell, presumably some kind of fermenter utilizing organic materials of the primordial soup as its food substance to evolve to the level of complexity, both morphologically, genetically, metabolically of cyanobacteria 3.5 billion years ago, 300 million years. Microbiologists seem to be very reluctant to accept 300 million years for this time of evolution. It's not that they think of evolution in a different way, it's that Cyanobacteria are really very complex bacteria. A very interesting thing, that 300 million years isn't enough. Well, again, we don't know when the origin of life occurred. Maybe it could go back 4.4 billion years, but with the impacting, it's highly unlikely that something could have survived from that time.

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