CINCINNATI, Nov. 29 (UPI) -- Scientists have found fossil evidence of bacteria in ancient rocks at two separate locations in South Africa. The findings offer a glimpse of life on Earth prior to the advent of oxygen abundance.
"These are the oldest reported fossil sulfur bacteria to date," Andrew Czaja, an assistant professor of geology at the University of Cincinnati, said in a news release. "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."
The fossil bacteria hail from the Neoarchean Eon and are estimated to be 2.52 billion years old. The fossils feature large, round, smooth-walled microscopic structures -- much larger than modern bacteria. Their size and shape recall modern single-celled species found near sulfur vents at the bottom of the ocean.
The bacteria found in the ancient South African rocks once lived underwater, too.
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"These fossils represent the oldest known organisms that lived in a very dark, deep-water environment," said Czaja. "These bacteria existed two billion years before plants and trees, which evolved about 450 million years ago. We discovered these microfossils preserved in a layer of hard silica-rich rock called chert located within the Kaapvaal craton of South Africa."
The bacteria featured in the new study -- published this week in the journal Geology -- evolved during the time of the Vaalbara supercontinent. It thrived upon deep seabeds in ocean water rich in sulfur leached from continental rock. The bacteria remained abundant, even as bacteria in shallower water began emitting large amounts of oxygen as a byproduct of photosynthesis.
"We refer to this period as the Great Oxidation Event that took place 2.4 to 2.2 billion years ago," says Czaja.
Researchers believe the ancient bacteria recycled volcanic hydrogen sulfide, turning it into sulfide -- just like modern bacteria.
"While I can't claim that these early bacteria are the same ones we have today, we surmise that they may have been doing the same thing as some of our current bacteria," said Czaja. "These early bacteria likely consumed the molecules dissolved from sulfur-rich minerals that came from land rocks that had eroded and washed out to sea, or from the volcanic remains on the ocean's floor."
