An international team of researchers discovered a type of deep-sea microorganism that appears to have remained unchanged for over 2 billion years. There are many species considered living fossils because they remained very similar in the course of many million of years but this is a really extreme case. Those are sulfu-cycling microorganisms that are now found in mud off the coast of Chile and are indistinguishable from fossils that date back to different past eras.
J. William Schopf, professor of Earth, Planetary and Space Sciences at the UCLA College, is the lead author of this research, published in the journal “Proceedings of the National Academy of Sciences” (PNAS). He and his team of researchers used several techniques to analyze the fossils and compare those of different ages between them and with modern microorganisms.
Among the techniques there’s Raman spectroscopy, which allows scientists to look inside rocks to determine their composition and their chemical characteristics thanks to a laser. The researchers also used confocal laser scanning microscopy which allows to render fossils in 3D. J. William Schopf is a pioneer of the use of both techniques for the analysis of microscopic fossils in ancient rocks.
The analysis focused on fossil microorganisms dating back 1.8 billion years ago preserved in rocks in Western Australia’s coast and other fossils found in the same region dating back to 2.3 billion years ago. The result was that the two fossils look the same and that those ancient bacteria are indistinguishable from modern ones.
Those bacteria date back to the period of the great oxydation, a great mass extinction occurred between 2.2 and 2.4 billion years ago when oxygen levels increased dramatically. The oxygen was poisonous for anaerobic primitive life forms, which succumbed to those who could tolerate oxygen.
That event also produced a significant increase of sulfates and nitrates, the only nutrients needed by the bacteria studied by Professor Schopf and his team. At that point, they were able to thrive in an environment that became very stable, so much that the conditions remained virtually unchanged until today.
Professor Schopf stated that the stability of the bacteria should be considered evidence for evolution. This may seem a paradox but is explained by the fact that these organisms are perfectly adapted to an environment that remained unchanged and are very simple. The consequence is that natural selection favored no genetic mutations. In 2 billion years there may have still been some genetic changes but they were too limited to produce relevant changes in those bacteria.
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