A team of scientists has discovered a remarkable type of deep-sea bacterium that appears to have remained essentially unchanged for over 2 billion years. To put that into perspective, that’s almost half the age of our planet. Interestingly, rather than contradicting Darwin’s theory of evolution, this example of extreme stasis actually lends support to Darwinian evolution.
As described in the Proceedings of the National Academy of Sciences journal, the discovery was made after UCLA scientists examined ancient communities of fossil bacteria preserved in 1.8-billion-year-old rock from the coast of Western Australia. Using a combination of spectroscopic and microscopic techniques, the researchers were able to gain an insight into the composition and chemistry of the rocks, and also produce 3D images of the microbes inside.
These data revealed that the microorganisms, which are sulfur-cycling bacteria, are virtually identical to another community of fossil microbes 500 million years older and discovered in 2.3-billion-year-old rock, once again from an ancient coastal formation in Western Australia. Furthermore, both of these communities are almost indistinguishable from modern sulfur-cycling bacteria found in mud off the coast of South America.
Given that evolution is well substantiated, how can this example of apparent stasis be explained? Interestingly, it actually supports an important aspect of Darwinian evolution. As described in the publication: “If there is no change in the physical-biological environment of a well-adapted ecosystem, its biotic components should similarly remain unchanged.”
In other words, if an organism is well adapted to its environment, and this environment does not change, then there is no need to evolve. Indeed, the environment in which these microbes reside has remained essentially unaltered for some 3 billion years. Conversely, if the microbes did evolve in spite of a stable, unchanging environment, then this would be inconsistent with the theory of evolution.
“The rule of biology is not to evolve unless the physical or biological environment changes, which is consistent with Darwin,” Schopf explained. Of course, in the absence of DNA sequence data, it is impossible to assert that they have not evolved at all. However, the morphological data obtained would suggest that they have changed very little over time.
The ancient fossils described in the study date back to shortly after a period that changed the history of life on Earth: the “Great Oxidation Event,” which occurred some 2.4 to 2.2-billion-years-ago. Early on in our planet’s history, Earth’s atmosphere was devoid of oxygen. But during this world-changing event, atmospheric concentrations of oxygen began to rise to appreciable levels. Concomitantly, levels of sulfate and nitrate also dramatically increased, which deep sea, mud-dwelling organisms would have thrived on.