LSU Researcher Finds new way to Look at Earth’s Frozen Past

Huiming Bao and collaborators find new evidence testing “snowball Earth” theory

Building off of a ground-breaking study published in Nature last summer, Huiming Bao and colleagues from around the world have discovered a new line of evidence supporting a truly alien Earth condition which took place approximately 635 million years ago, when the Earth is believed to have just recovered from a “snowball” state. During this time, the planet was covered entirely by ice for several millions of years. Their findings were published in the Jan. 2 issue of Science.

“The size of our original measurement of the oxygen-17 anomaly, though large enough to preclude any analytical errors, still left doubt in the minds of many in the scientific community,” said Bao. “Our new findings are large enough that they should easily dismiss any continuing disbelief.”

Bao’s original research found an oxygen-17 anomaly of –0.70 per mil (meaning for every thousand); the team’s new measurements weigh in with a value of –1.64 per mil, and are from a different mineral host.

Oxygen-17 anomalies are usually not measured by scientists who study Earth rocks because they were originally believed to be exclusively extra-terrestrial in nature, coming only from specific types of asteroids. Over the years, Bao’s group has worked on many extremely dry deserts on Earth and shown that there are a large range of oxygen-17 anomalies among desert salts that record atmospheric reactions. All of the previous documented anomalies are positive, meaning that there is an excess in the oxygen-17 isotopes. This finding, however, reveals a large depletion in oxygen-17 content in some of the sulfate minerals. These – along with Bao’s previous results – are the first oxygen-17 depletions, or negative anomalies, found in Earth minerals. What is even more striking is the timing of the negative anomalies – there is a spike in the depletion right at the time when a global glaciation came to an abrupt end approximately 635 million years ago.

Following Bao’s initial model, the newly discovered, much larger anomalies would suggest a much higher atmospheric carbon dioxide level at the time of glacial melting – a scenario strongly favoring the “snowball Earth” hypothesis. In the Science study, however, Bao and his colleagues also caution about dismissing other scenarios.

“We’re still not ready to declare a verdict on the feasibility of a snowball Earth scenario,” said Bao. “There are still more tests that need to be run and models that must be constructed, but the results of our research definitely bring us that much closer to resolution.”

The discovery is of particular timeliness as the world grows increasingly concerned about the potential impacts of global climate change, especially factors that can trigger the Earth system into or out of an extreme state. In fact, a “White Earth” scenario very similar to snowball Earth was one of the likely results when scientists were trying to model changes that might occur in the atmosphere in the case of a nuclear war.

Bao’s team includes Ian Fairchild from the University of Birmingham, U.K.; Peter Wynn of the University of Lancaster, also in the U.K.; and Christoph Spötl of the Leopold-Franzens-Universität Innsbruck, Austria. The group took measurements from the Arctic region of Svalbard, Norway, an area that is more difficult to conduct fieldwork in than even Antarctica. The samples used in this study were collected during an expedition in the 1980s by Fairchild and his colleagues.

“In at least two fronts, our data breaks the current known natural ranges of sulfate’s oxygen isotope compositions. Additionally, correlations among the data strengthened our interpretation,” said Bao. “An extraordinary surface environment is revealed by an extraordinary multi-stable-isotope dataset for an extraordinary time period in Earth history.”

For more information, contact Huiming Bao at bao@lsu.edu or 225-578-3419.

Ashley Berthelot | Writer | Office of Communications & University Relations
January 2009