University of California (UC) Riverside geoscientists help tie spike in ancient oceanic oxygen levels to ‘Snowball Earth’ event
An international team of scientists, including geochemists from the UC Riverside, has uncovered new evidence linking extreme climate change, oxygen rise, and early animal evolution. A dramatic rise in atmospheric oxygen levels has long been speculated as the trigger for early animal evolution. While the direct cause-and-effect relationships between animal and environmental evolution remain topics of intense debate, all this research has been hampered by the lack of direct evidence for an oxygen increase coincident with the appearance of the earliest animals — until now.
In the September 27 issue of the journal Nature, the research team, led by scientists at the University of Nevada, Las Vegas, offers the first evidence of a direct link between trends in early animal diversity and shifts in Earth system processes. The fossil record shows a marked increase in animal and algae fossils roughly 635 million years ago. An analysis of organic-rich rocks from South China points to a sudden spike in oceanic oxygen levels at this time — in the wake of severe glaciation. The new evidence pre-dates previous estimates of a life-sustaining oxygenation event by more than 50 million years.
The research team analysed concentrations of trace metals and sulfur isotopes, which are tracers of early oxygen levels, in mudstone collected from the Doushantuo Formation in South China. The team found spikes in concentrations of the trace metals, denoting 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 UC Riverside graduate student in Lyons’s lab now at CalTech.
The high element concentrations found in the South China rocks are comparable to modern ocean sediments and point to a substantial oxygen increase in the ocean-atmosphere system around 635 million years ago. 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.
Lyons and Planavsky argued in research published earlier in the journal Nature that a nutrient surplus associated with the extensive glaciations may have initiated intense carbon burial and oxygenation. Burial of organic carbon — from photosynthetic organisms — in ocean sediments would result in the release of vast amounts of oxygen into the ocean-atmosphere system.
The above news item is reprinted from materials available at University of California, Riverside. Original text may be edited for content and length.
(Source: UC Riverside Today, 26.09.2012)