2.5 Billion-Year-Old Bacteria Fossils Predate the Formation of Oxygen
While researchers proclaim the first half of our 4.5 billion-year-old planet’s life as an important time for the development and evolution of early bacteria, evidence for these life forms remains sparse.
Recent geology research from the University of Cincinnati presents new evidence for bacteria found fossilized in two separate locations in the Northern Cape Province of South Africa.
“These are the oldest reported fossil sulfur bacteria to date,” says Andrew Czaja, UC assistant professor of geology. “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.”
This work was supported by the National Geographic Society–Waitt Grant Program and the NASA Astrobiology Institute.
The 2.52 billion-year-old sulfur-oxidizing bacteria are described by Czaja as exceptionally large, spherical-shaped, smooth-walled microscopic structures much larger than most modern bacteria, but similar to some modern single-celled organisms that live in deepwater sulfur-rich ocean settings today.
In his research published in the December issue of the journal Geology of the Geological Society of America, Czaja and his colleagues Nicolas Beukes from the University of Johannesburg and Jeffrey Osterhout, a recently graduated master’s student from UC’s department of geology, reveal samples of bacteria that were abundant in deep water areas of the ocean in a geologic time known as the Neoarchean Eon (2.8 to 2.5 billion years ago).
“These fossils represent the oldest known organisms that lived in a very dark, deep-water environment,” says 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.”
With an atmosphere of much less than one percent oxygen, scientists have presumed that there were things living in deep water in the mud that didn’t need sunlight or oxygen, but Czaja says experts didn’t have any direct evidence for them until now.
Czaja argues that finding rocks this old is rare, so researchers’ understanding of the Neoarchean Eon are based on samples from only a handful of geographic areas, such as this region of South Africa and another in Western Australia.
According to Czaja, scientists through the years have theorized that South Africa and Western Australia were once part of an ancient supercontinent called Vaalbara, before a shifting and upending of tectonic plates split them during a major change in the Earth’s surface.
Based on radiometric dating and geochemical isotope analysis, Czaja characterizes his fossils as having formed in this early Vaalbara supercontinent in an ancient deep seabed containing sulfate from continental rock. According to this dating, Czaja’s fossil bacteria were also thriving just before the era when other shallow-water bacteria began creating more and more oxygen as a byproduct of photosynthesis.