Scientists reveal a new part of the recipe for complex life on planets, and it involves the onset of a microbial fertilizer factory on the Earth's seafloor roughly 2.6 billion years ago. During the early stages of the Great Oxidation Event, the first big rise in oxygen levels on Earth occurred around 2.4 to 2.2 billion years ago.
The Great Oxidation Event:
Why and how the Great Oxidation Event happened is still a mystery to scientists. Some researchers believe it was triggered by growing phosphorus levels in the ocean, which promoted photosynthesis and increased oxygen production, while others believe it was caused by a decrease in the release of reactive gases from volcanoes, which consumed less of the oxygen generated.
Now, a group of international scientists led by the University of Leeds has employed a new approach to assess phosphorus cycling between the ocean and the seafloor in 2.6 billion-year-old rocks from South Africa, which occurred prior to the Great Oxidation Event.
Laboratory tests on these rocks reveal that recycling phosphorus back into saltwater fueled photosynthetic microorganisms, which raised oxygen levels.
Their research, which was published today in Nature Geoscience, found that the formation of this "seafloor fertiliser factory" was a prerequisite for the rise of oxygen levels on Earth, and that it could be a key element in the ability of other planets to support sophisticated life.
While a Ph.D. student in Leeds' School of Earth and Environment, Lewis Alcott, who is currently working at Yale University in the United States, led the research. "It's possible that this process is fundamental to a planet being oxygenated and thus able to house complex life," he said.
"Untangling the recipe for an oxygen-rich environment can help us assess the likelihood of similar events occurring on other planets."
Professor Simon Poulton of Leeds' School of Earth and Environment, the study's senior author, said: "The availability of sulphate, which is an important component of the recycling process, is a crucial aspect of this recipe. As a result, an abundance of sulphur could be a crucial necessity for a world that is oxygenated."
The growth of atmospheric oxygen during the 2.4 billion-year-old Great Oxidation Event was a watershed moment in the evolution of global biogeochemical cycles and life on Earth. However, a rising body of evidence suggests that cyanobacteria began producing oxygen hundreds of millions of years before the Great Oxidation Event.
"This early oxygen production led to an increase in seawater sulphate, which kicked-started the recycling process, allowing oxygen production rates to climb enough to oxygenate the atmosphere," stated study co-author Dr. Andrey Bekker of the University of California, Riverside.
"This work not only furthers our understanding of the history of our planet but also helps us comprehend its current activities," stated lead Ph.D. supervisor and study co-author Dr. Benjamin Mills of the School of Earth and Environment.
"There is concern that the same phosphorus recycling process has contributed to dangerous ocean anoxic occurrences, because it oxygenates the atmosphere while removing oxygen from the water as photosynthetic bacteria decay. As a result of climate change, it is starting to do so now. Ocean oxygen levels are falling as a result of a combination of rising temperatures and increased usage of phosphorus as an agricultural fertilizer."
(Source: University of Leeds)
