Oxygen production by photosynthetic cyanobacteria may have initiated as early as three billion years ago, much earlier than previously thought, scientists say.
Researchers at the University of California, Riverside provide a nontraditional way of thinking about the earliest accumulation of oxygen in the atmosphere, arguably the most important biological event in Earth history.
A general consensus asserts that appreciable oxygen first accumulated in Earth's atmosphere around 2.3 billion years ago during the so-called Great Oxidation Event (GOE).
However, according to new research, oxygen production by photosynthetic cyanobacteria may have initiated as early as 3 billion years ago.
Oxygen concentrations in the atmosphere potentially rose and fell episodically over many hundreds of millions of years, reflecting the balance between its varying photosynthetic production and its consumption through reaction with reduced compounds such as hydrogen gas, researchers have found.
"There is a growing body of data that points to oxygen production and accumulation in the ocean and atmosphere long before the GOE," said Timothy W Lyons, lead author of the study.
Lyons and his coauthors note that once oxygen finally established a strong foothold in the atmosphere starting about 2.3 billion years ago it likely rose to high concentrations, potentially even levels like those seen today.
Then, for reasons not well understood, the bottom fell out, oxygen plummeted to a tiny fraction of today's level, and the ocean remained mostly oxygen free for more than a billion years, researchers said.
"This period of extended low oxygen spanning from roughly 2 to less than 1 billion years ago was a time of remarkable chemical stability in the ocean and atmosphere," Lyons said.
His research team envisions a series of interacting processes, or feedbacks, that maintained oxygen at very low levels principally by modulating the availability of life-sustaining nutrients in the ocean and thus oxygen-producing photosynthetic activity.
"We suggest that oxygen was much lower than previously thought during this important middle chapter in Earth history, which likely explains the low abundances and diversity of eukaryotic organisms and the absence of animals," Lyons said.
The research appears in the journal Nature.