An international team of scientists has found a deep-sea microorganism that appears to have not changed over the course of two billion years. The researchers said that the discovery of an organism that has not evolved for such a long period of time bolster's Charles Darwin's theory of evolution.

For their study published in the Proceedings of the National Academy of Sciences on Feb. 2, J. William Schopf, from the Department of Earth, Planetary, and Space Sciences at the University of California, Los Angeles, and colleagues looked at 1.8 billion year old sulfur bacteria, which are too small to be seen with an unaided eye that were preserved in the rocks found in the coastal waters of Western Australia.

The researchers then compared the bacteria to those that thrived in the same region 2.3 billion years ago. They likewise found that both microbes were indistinguishable from present-day sulfur bacteria that can be found off the coast of Chile.

Schopf and colleagues used Raman spectroscopy to measure the rocks' composition and chemistry, and with the aid of confocal laser scanning microscopy, produced three dimensional images of the fossils, which they compared with those of the modern bacteria revealing that the ancient microbes and the present days ones look identical.

The fossils that the researchers looked into date back to the Great Oxidation event 2.2 billion to 2.4 billion years ago, which was marked by a surge of oxygen levels on Earth. During this period, the sulfate and nitrate levels have largely increased, providing all the necessary nutrition for the sulfur bacteria to survive and reproduce.

The environment inside these deep-sea rocks have notably remained unchanged so the organisms do not need to adapt and this gives credence to Darwin's theory of evolution by natural selection that states all species of organisms develop from heritable genetic changes that increases the organism's ability to survive, compete and reproduce.

Schopf said that Darwin's theory does not call for organisms to evolve if there are no environmental changes so the lack of evolution seen in the microbes is consistent with the theory. The researchers, however, said that further evidence is still needed to establish this.

"Although the apparent 2-billion-year-long stasis of such sulfur-cycling ecosystems is consistent with the null hypothesis required of Darwinian evolution-if there is no change in the physical-biological environment of a well-adapted ecosystem, its biotic components should similarly remain unchanged-additional evidence will be needed to establish this aspect of evolutionary theory," the researchers wrote.