In a remarkable breakthrough, researchers have find fossils of sulfur-oxidising bacteria that are nearly 2.5 billion-year-old. What’s striking about the bacteria is they thrived in the absence of oxygen. The discovery suggests that the ancient lifeform had the ability to survive without oxygen and they could thrive even in limited oxygen supply.
The ancient fossils have been recovered from two different locations in the Northern Cape Province of South Africa. Researchers claim that these are the oldest fossils of sulphur bacteria discovered till date.
“These are the oldest reported fossil sulfur bacteria to date,” said Andrew Czaja, Assistant Professor of Geology at University of Cincinnati in the US. “And this discovery is helping us reveal a diversity of life and ecosystems that existed just prior to the Great Oxidation Event, a time of major atmospheric evolution,” Czaja noted.
Scientists know that composition of oxygen was very less in Earth’s atmosphere in early days and shallow water bacteria started creating more and more oxygen as a by-product of photosynthesis which increased oxygen levels and further initiated the evolution of species. Experts call this period as the Great Oxidation Event that occurred between 2.4 to 2.2 billion years ago.
However, these newly discovered bacteria were thriving even before the Great Oxidation Event when oxygen supply was very less. These bacteria had smooth-walled microscopic structure and were much larger than the bacteria of present day.
“These fossils represent the oldest known organisms that lived in a very dark, deep water environment,” Czaja said. “We discovered these microfossils preserved in a layer of hard silica-rich rock called chert located within the Kaapvaal craton of South Africa,” Czaja noted.
Study authors calculated and found that the era had less than 1 percent oxygen in the atmosphere so they presumed that some organisms must be living underwater in the mud that did not require sunlight or oxygen to survive. However, they don’t have enough evidence to prove it.
Study authors explained that those bacteria got their energy from hydrogen sulphide or sulphur rich minerals that came from land rocks and they would have released sulphur as their waste product. Also, they would have consumed other microbes to survive while some different species would have fed on sulphur wastes.
The study appeared in the journal Geology.