News: Researchers Find Ancient Evidence of 'Snowball Earth'
- From: "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx>
- Date: Mon, 14 Jul 2008 02:02:58 -0400 (EDT)
Researchers Find Ancient Evidence of 'Snowball Earth'
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."
Source: LSU
http://www.physorg.com/news135005681.html
Posted by
Robert Karl Stonjek
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