#Fossils #Science – 2.5-Billion-Year-Old Fossils Predate Earth’s Oxygen  : Fossils of what may be the oldest sulfur-eating bacteria ever found have been discovered in rocks dating back a staggering 2.52 billion years.

The fossils don’t represent the oldest life on Earth by any stretch — there are fossils of microbes that are at least a billion years older — but they are the oldest of their type. They also illuminate a mysterious phase of geologic history, when there was hardly any oxygen in the air and photosynthesis — the process that would eventually oxygenate the atmosphere — had just evolved, said study leader Andrew Czaja, a geologist at the University of Cincinnati.

Rather than using oxygen to survive, these bacteria would have turned hydrogen sulfide into sulfate (the oxidized form of sulfur), using the energy from that chemical reaction to grow, Czaja said.


“Everything was evolving; all these different bacterial metabolisms were evolving,” Czaja said. [7 Wild Theories on the Origin of Life]