November 1, 2010

“˜Snowball Effect’ Linked To Emergence Of Life

(Ivanhoe Newswire) -- A team of scientists have discovered that evidence linking the "Snowball Earth" glacial events to the emergence of complex life.

The Snowball Earth hypothesis states that the Earth was covered from pole to pole by a thick sheet of ice lasting, on several occasions, for millions of years. These glaciations were the most severe in Earth history. They occurred 750 to 580 million years ago. The researchers argue that the oceans in the aftermath of these events were rich in phosphorus, a nutrient that controls the abundance of life in the oceans.

A team of researchers and colleagues from the University of California, Riverside tracked phosphorus concentrations through Earth's history. They analyzed the composition of iron-rich chemical precipitates that accumulated on the sea floor and scavenged phosphorus from seawater.

To explain the unbelievably high concentrations of phosphorus, the researchers argue that the increase in erosion and chemical weathering on land that accompanies Snowball Earth glacial events led to the high amount in phosphorus in the ocean. The abundance of this nutrient led to a spike in oxygen production via photosynthesis and its accumulation in the atmosphere, facilitating the emergence of complex life.

"In the geological record, we found a signature for high marine phosphorus concentrations appearing in the immediate aftermath of the Snowball Earth glacial events," Noah Planavsky, the first author of the research paper and a graduate student in the Department of Earth Sciences was quoted as saying. "Phosphorus ultimately limits net primary productivity on geological timescales. Therefore, high marine phosphorus levels would have facilitated a shift to a more oxygen-rich ocean-atmosphere system. This shift could have paved the way for the rise of animals and their ecological diversification. Our work provides a mechanistic link between extensive Neoproterozoic glaciations and early animal evolution."

Planavsky explained the link between marine phosphorus concentrations and the levels of oxygen in the atmosphere.

"High phosphorus levels would have increased biological productivity in the ocean and the associated production of oxygen by photosynthesis," he said. "Much of this organic matter is consumed, in turn, as a result of respiration reactions that also consume oxygen. However, the burial of some proportion of the organic matter results in a net increase of oxygen levels in the atmosphere."

Until now, scientists believed that geochemical conditions in the ocean would have led to low phosphorus concentrations. The UC Riverside researchers found no evidence of a phosphorus crisis after Snowball Earth glacial events, however, instead finding indications of an abundance of phosphorus.

"There are several known chemical fingerprints for increasing oxygen in the ocean and, by inference, in the atmosphere during the middle part of Neoproterozoic, and the rise of animals is an expected consequence," Timothy LyonsTimothy Lyons, a professor of biogeochemistry and the senior investigator in the study was quoted as saying. "But our results may be the first to capture the nutrient driver that was behind this major step in the history of life, and that driver was ultimately tied to the extreme climate of the period."

SOURCE: Nature, published online October 27, 2010