LSU scientist Huiming Bao, along with colleagues from UCLA and China, recently discovered some of the first atmospheric evidence in support of the “Snowball Earth” hypothesis. This theory suggests that Earth was entirely covered by ice during the Cryogenian period, which took place from about 790 to 630 million years ago. Their findings were reported in the May 22 issue of Nature.
Bao and his group used a new parameter called “sulfate oxygen-17 anomaly” to measure atmospheric records found in mineral sulphate deposits. “My group specializes in measuring these anomalies – very few other groups do,” said Bao. “This puts us in an extremely good position for uncovering previously unknown information.”
These 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 oxygen-17 isotopes. This finding, however, reveals a large depletion in oxygen-17 content in some of the sulfate minerals. These 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.
To account for the data, Bao and his colleagues proposed that this depletion spike was caused by an extremely high atmospheric carbon dioxide concentration at that time, at least 40 times the modern level. That is what the “Snowball Earth” hypothesis predicted when the entire oceans were frozen over for millions of years. Bao and his colleagues will still have to rule out other scenarios before calling their evidence a “smoking gun” for the theory. “But we have found a new way to look into the details of very old glaciations events that other approaches couldn’t,” said Bao. “Using this new parameter, we should be able to read from the rock record the dynamics of the glaciations as well as the impact to biosphere, atmosphere and hydrosphere of our Earth system.”
In light of the increasing environmental stresses humans have placed on Earth, Bao said that there is a critical need to understand how a complex system like Earth’s can be expected to react.
“There is an old saying that the best way to know a person’s character is to put him or her under pressure and see how he reacts,” said Bao. “This is the same situation. The best way to learn more about our Earth system is to see how it responded to extreme conditions in the past.”