“Snowball Earth” may not be responsible for mass extinction of early life on Earth

May 27th, 2009 - 12:12 pm ICT by ANI  

Washington, May 27 (ANI): New fossil findings discovered by scientists have challenged the prevailing views about the effects of “Snowball Earth” glaciations on life, which is presumed to be responsible for widespread die-off of early life on Earth.

By analyzing microfossils in rocks from the bottom of the Grand Canyon, the scientists from UC (University of California) Santa Barbara have challenged the view that has been generally assumed to be correct for the massive extinction of early life on Earth.

“Snowball Earth” is the popular term for glaciations that occurred between approximately 726 and 635 million years ago and are hypothesized to have entombed the planet in ice, explained co-author Susannah Porter, assistant professor of earth science at UCSB.

It has long been noted that these glaciations are associated with a big drop in the fossil diversity, suggesting a mass die-off at this time, perhaps due to the severity of the glaciations.

However, the research team found evidence suggesting that this drop in diversity occurred some 16 million or more years before the glaciations.

They offer an alternative reason for the drop.

A location called the Chuar Group in the Grand Canyon serves as “one of the premier archives of mid-Neoproterozoic time,” according to the research.

This time period, before Snowball Earth, is preserved as a sort of “snapshot” in the canyon walls.

The scientists found that diverse assemblages of microscopic organic-walled fossils called acritarchs, which dominate the fossil record of this time, are present in lower rocks of the Chuar Group, but are absent from higher strata.

In their place, there is evidence for the bacterial blooms that, the researchers hypothesize, most likely appeared because of an increase in nutrients in the surface waters.

This process is known as eutrophication, and occurs today in coastal areas and lakes that receive abundant runoff from fertilizers used in farming.

“One or a few species of phytoplankton monopolizes nutrients at the expense of others,” said Porter, explaining the die-off of diverse acritarchs.

“In addition, the algal blooms result in high levels of organic matter production, which we see evidence of in the high organic carbon content in upper Chuar Group rocks. As a result of high levels of organic matter, oxygen levels in the water can become depleted, resulting in widespread “dead zones”,” she added.

Porter and colleagues also found evidence for extreme anoxia in association with the bacterial blooms. (ANI)

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