London: A new study has analysed bacterial colonies called microbial mats in the Los Roques lagoons of Venezuela and found that it offered a refuge of oxygen-rich sediment.
Mats of plant-like bacteria dramatically increase local oxygen levels in the lakes where they are found, as a result of photosynthesis. That might have given early multicellular animals the boost they needed to evolve in an ancient world where oxygen was scarce.
Murray Gingras, a palaeontologist at the University of Alberta in Edmonton, Canada, examined the chemistry of the water above and inside the living mats.
He and his colleagues found that although oxygen levels in the surface waters of the lagoon were very low, often reaching 0.10 units of atmospheric pressure (atm), daytime levels in deeper waters near the mat rose to between 0.25 and 0.45 atm as the bacteria produced energy from sunlight and released oxygen as a waste product.
They propose that the mats had a key role in helping early animals to get the oxygen they needed.
"We think that animals used the small but highly oxygenated zones as oases," said Gingras.
For long, palaeontologists have theorized that early animals fed on microbial mats, because fossils of animals and mats are often found together. But this is the first time that researchers have shown how mats can function as important oxygen resources for fauna.
The study appears in Nature Geoscience.