Iron-silica particles reveal early oxygen accumulation on Earth

Aug. 7 (UPI) -- Iron and silica particles played an important part in the early accumulation of oxygen in Earth's oceans, according to new research.

Cyanobacteria's photosynthetic activity supplied Earth's ancient oceans with oxygen, but the blue-green algae couldn't have survived the sun's ultraviolet rays without the protection of iron and silica particles, according to a new study in the journal Nature Communications.

In the lab, scientists modeled the impact of UV rays on ancient sea water and cyanobacteria. The experiments showed elevated silica and iron concentrations enable the formation of iron-silica precipitates. These suspended particles shielded cyanobacteria from harmful radiation.

"In effect, the iron-silica particles acted as an ancient 'sunscreen' for the cyanobacteria, protecting them from the lethal effects of direct UV exposure," Kurt Konhauser, professor of earth and atmospheric sciences at the University of Alberta, said in a news release. "This was critical on the early Earth before a sufficiently thick ozone layer was established that could enable marine plankton to spread across the globe, as is the case today."

While the latest research helps explain how oxygen first accumulated in Earth's oceans, scientists still aren't sure how oxygen levels grew large enough to dramatically alter atmospheric oxygen concentrations.

Despite the protection offered by suspended iron-silica precipitates, UV radiation still would have limited the growth of cyanobacteria.

"It is likely that early cyanobacteria would not have been as productive as they are today because of the effects of UV stress," said Aleksandra Mloszewska, former Alberta PhD student. "Until the accumulation of sufficient cyanobacteria-derived oxygen allowed a more permanent means of protection to develop, such as an ozone layer, UV stress may have played an even more important role in shaping the structure of the earliest ecosystems."

By better understanding how Earth's life-friendly chemistry evolved, researchers can better predict how habitability on faraway planets might develop.

"These findings could also be used as a case study to help us understand the potential for the emergence of life on other planets that are affected by elevated UV radiation levels," said Mloszewska.