An analysis of 1.8 billion-year-old bacterial fossils trapped in West Australian rocks revealed that the microbes were nearly identical both to fossils that are half a billion years older and to modern-day bacteria found in a similar ecosystem off the coast of South America, according to a study published last week (February 2) in PNAS. The finding provides evidence for a corollary of Darwin’s theory of evolution: if an environment does not change over time, organisms need not evolve and can survive without changes to their lifestyle.
Using spectroscopy and confocal microscopy to examine the fossil-bearing rocks, a team of American, Australian, and Chilean scientists demonstrated that the shape of individual bacteria and the structure of their communities were highly similar to a 2.3 billion-year-old fossil previously found in Australia as well as to sulfur-metabolizing bacteria found in Chilean mud in 2007. The oldest of these bacteria arose after the Great Oxygenation Event, which led to an increase in the sulfate and nitrate nutrients that the bacteria consume in their muddy environment.
“These microorganisms are well-adapted to their simple, very stable physical and biological environment,” study coauthor J. William Schopf of the University of California, Los Angeles, said in a statement. “If they were in an environment that did not change but they nevertheless evolved, that would have shown that our understanding of Darwinian evolution was seriously flawed.”
Confirming the corollary, however, will require studies of the molecular biology of the ancient and modern organisms, as well as other examples of organisms that have not undergone change in constant environments, the authors wrote in their paper.