Did ‘Snowball Earth’ Epoch Trigger Rise of Animals?

Snowball_Earth Before 50 million years ago the planet had no cyclical ice ages. What it did have was a pair of glacial whoppers: one about two billion years ago, followed by a billion years of warmth and another mega ice age called the Cryogenian (you get the picture!) when temperatures plunged 80 degrees Fahrenheit, creating a global Antarctica, dubbed by pundits as "Snowball Earth."

New research on the Snowball Earth epoch shows it may have had a dramatic effect on the evolutionary history of the planet. Using a core is from the approximately 2.2 billion-year-old Hotazel Formation from South Africa a University of California, Riverside team found "a signature for high marine phosphorus concentrations appearing in the immediate aftermath of the Snowball Earth glacial events," according to Noah Planavsky.

"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 iron-rich 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, finding instead 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," said Timothy Lyons, a professor of biogeochemistry and the senior investigator in the study. "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."

The researchers present data from approximately 700 individual samples of iron-oxide-rich rocks that included new results as well as those obtained from a comprehensive survey of the literature.

Casey Kazan via University of California — Riverside


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