Early Evolution Linked To Climate Change And Oxygen Levels
September 28, 2012

Researchers Link Early Evolution Of Animals To Climate Change And Oxygen Levels

April Flowers for redOrbit.com - Your Universe Online

Geochemists from the University of California, Riverside teamed up with an international team of scientists to uncover new evidence linking together extreme climate change, elevation of oxygen levels and early animal evolution.

Scientists have long speculated that a dramatic rise in atmospheric oxygen levels was the trigger for early animal evolution. The direct cause-and-effect relationships between environmental and animal evolution, however, has been the subject of heated debates, and a lack of direct evidence for the oxygen increase coinciding with the appearance of the earliest animals has hampered research until now.

The new study, led by researchers from the University of Nevada, Las Vegas, offers the first evidence of a direct link between patterns in early animal diversity and changes in Earth system processes. The findings were published in the September 27 issue of Nature.

Roughly 635 million years ago, the fossil record shows that there was a significant increase in the number and diversity of animals and algae. An analysis of organic-rich rocks from southern China points to a sudden spike in oceanic oxygen levels at this time directly after a severe glaciation. This new evidence pre-dates previous estimates by more than 50 million years for a life-sustaining oxygenation event.

"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.

The team looked for signs of oxygen levels by examining concentrations of trace metals and sulfur isotopes in mudstone collected from the Doushantuo Formation in South China. They found spikes in concentrations of the trace metals, which denotes higher oxygen levels in seawater on a global scale.

The Doushantuo Formation is one of the planet´s oldest fossil beds and contains a vast array of well preserved fossils. It appears to cover the boundary between the problematic organisms of the Ediacaran and the well-known flora of the Cambrian geological periods.

"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.

The researchers say that the concentrations found in the Doushantuo rocks are comparable to modern ocean sediments. This points to a substantial oxygen increase in the ocean-atmosphere system around 635 million years ago. The team believes that this oxygen rise was likely due to increased organic carbon burial, a result of more nutrient availability following the extremely cold climate of the "Snowball Earth" glaciation when ice shrouded much of Earth's surface.

The Snowball Earth theory states that the Earth's surface was entirely or nearly entirely frozen at least once, sometime prior to 650 million years ago.

Earlier research by the same team showed that a nutrient surplus associated with the extensive glaciations may have initiated intense carbon burial and oxygenation. Organic carbon, from photosynthetic organisms, buried in ocean sediments would result in the release of vast amounts of oxygen into the ocean-atmosphere system.

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