Early Animal Evolution Due to Oxygen Rise

It has long been speculated that the rise in atmospheric oxygen levels is responsible for early animal evolution. But many studies failed to provide a direct cause and effect relationships between animal and environmental evolution. This was because of the lack of direct evidence for an oxygen increase.

But for the first time an international team of scientists, including geochemists from the University of California, offers the first evidence of a direct link between trends in early animal diversity and shifts in Earth system processes. They have linked extreme climate change, oxygen rise and early animal evolution.

The details of this study will be published in the Sept 27 issue of the Journal Nature. And the study was led by scientists at the University of Nevada, Las Vegas.

The fossil record shows a marked increase in animal and algae fossils roughly 635 million years ago. They conducted an analysis of the organic rich rocks from the South China points to a sudden spike in the oceanic oxygen levels at this time during glaciation.

"This work provides the first real evidence for a long speculated change in oxygen levels in the aftermath of the most severe climatic event in Earth's history -- one of the so-called 'Snowball Earth' glaciations," said Timothy Lyons, a professor of biogeochemistry at UC Riverside.

Concentrations of trace metals and sulfur isotopes, which serve as perfect tracers of early oxygen levels, in mudstone were collected from the Doushantuo Formation in South China which were later analyzed by the research team.  They noticed spikes in concentrations of the trace metals, signifying higher oxygen levels in seawater on a global scale.

"We found levels of molybdenum and vanadium in the Doushantuo Formation mudstones that necessitate that the global ocean was well ventilated. This well-oxygenated ocean was the environmental backdrop for early animal diversification," said Noah Planavsky, a former UCR graduate student in Lyons's lab now at CalTech.

According to the researchers, "The oxygen rise is likely due to increased organic carbon burial, a result of more nutrient availability following the extreme cold climate of the 'Snowball Earth' glaciation when ice shrouded much of Earth's surface."

"We are delighted that the new metal data from the South China shale seem to be confirming these hypothesized events," Lyons said.