Argon Conclusion: Researchers Reassess Theories on Formation of Earth's Atmosphere (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 20 Sep 2007 15:01:39 GMT
Office of Media Relations
Rensselaer Polytechnic Institute
Contact: Gabrielle DeMarco
Phone: (518) 276-6542
For Immediate Release: September 19, 2007
Argon Conclusion: Researchers Reassess Theories on Formation of Earth's
Atmosphere
Troy, N.Y. -- Geochemists at Rensselaer Polytechnic Institute are
challenging commonly held ideas about how gases are expelled from the
Earth. Their theory, which is described in the Sept. 20 issue of the
journal Nature, could change the way scientists view the formation of
Earth's atmosphere and those of our distant neighbors, Mars and Venus.
Their data throw into doubt the timing and mechanism of atmospheric
formation on terrestrial plants.
Lead by E. Bruce Watson, Institute Professor of Science at Rensselaer, the
team has found strong evidence that argon atoms are tenaciously bound in
the minerals of Earth's mantle and move through these minerals at a much
slower rate than previously thought. In fact, they found that even
volcanic activity is unlikely to dislodge argon atoms from their resting
places within the mantle. This is in direct contrast to widely held
theories on how gases moved through early Earth to form our atmosphere and
oceans, according to Watson.
Scientists believe that shortly after Earth was formed, it had a glowing
surface of molten rock extending down hundreds of miles. As that surface
cooled, a rigid crust was produced near the surface and solidified slowly
downward to complete the now-solid planet. Some scientists have suggested
that Earth lost all of its initial gases, either during the molten stage
or as a consequence of a massive collision, and that the catastrophically
expelled gases formed our early atmosphere and oceans. Others contend that
this early "degassing" was incomplete, and that primordial gases still
remain sequestered at great depth to this day. Watson's new results
support this latter theory.
"For the 'deep-sequestration' theory to be correct, certain gases would
have to avoid escape to the atmosphere in the face of mantle convection
and volcanism," Watson said. "Our data suggest that argon does indeed stay
trapped in the mantle even at extremely high temperatures, making it
difficult for the Earth to continuously purge itself of argon produced by
radioactive decay of potassium."
Argon and other noble gases are tracer elements for scientists because
they are very stable and do not change over time, although certain
isotopes accumulate through radioactive decay. Unlike more promiscuous
elements such as carbon and oxygen, which are constantly bonding and
reacting with other elements, reliable argon and her sister noble gases
(helium, neon, krypton, and xenon) remain virtually unchanged through the
ages. Its steady personality makes argon an ideal marker for understanding
the dynamics of Earth's interior.
"By measuring the behavior of argon in minerals, we can begin to retrace
the formation of Earth's atmosphere and understand how and if complete
degassing has occurred," Watson explained.
Watson's team, which includes Rensselaer postdoctoral researcher Jay B.
Thomas and research professor Daniele J. Cherniak, developed reams of data
in support of their emerging belief that argon resides stably in crystals
and migrates slowly. "We realized from our initial results that these
ideas might cause a stir," Watson said. "So we wanted to make sure that we
had substantial data supporting our case."
The team heated magnesium silicate minerals found in Earth's mantle, which
is the region of Earth sandwiched between the upper crust and the central
core, in an argon atmosphere. They used high temperature to simulate the
intense heat deep within the Earth to see whether and how fast the argon
atoms moved into the minerals. Argon was taken up by the minerals in
unexpectedly large quantities, but at a slow rate.
"The results show that argon could stay in the mantle even after being
exposed to extreme temperatures," Watson said. "We can no longer assume
that a partly melted region of the mantle will be stripped of all argon
and, by extension, other noble gases."
But there is some argon in our atmosphere -- slightly less than 1 percent.
If it didn't shoot through the rocky mantle, how did it get into the
atmosphere?
"We proposed that argon's release to the atmosphere is through the
weathering of the upper crust and not the melting of the mantle," Watson
said. "The oceanic crust is constantly being weathered by ocean water and
the continental crust is rich in potassium, which decays to form argon."
And what about the primordial argon that was trapped in the Earth billions
of years ago? "Some of it is probably still down there," Watson said.
Because Mars and Venus have mantle materials similar to those found on
Earth, the theory could be key for understanding their atmospheres as
well.
Watson and his team have already begun to test their theories on other
noble gases, and they foresee similar results. "We may need to start
reassessing our basic thinking on how the atmosphere and other large-scale
systems were formed," he said.
The research was funded by the National Science Foundation.
About Rensselaer
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest
technological university. The university offers bachelor's, master's, and
doctoral degrees in engineering, the sciences, information technology,
architecture, management, and the humanities and social sciences.
Institute programs serve undergraduates, graduate students, and working
professionals around the world. Rensselaer faculty are known for
pre-eminence in research conducted in a wide range of fields, with
particular emphasis in biotechnology, nanotechnology, information
technology, and the media arts and technology. The Institute is well known
for its success in the transfer of technology from the laboratory to the
marketplace so that new discoveries and inventions benefit human life,
protect the environment, and strengthen economic development.
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