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Topic Name: Argon Conclusion: Researchers Reassess Theories on Formation of Earth’s Atmosphere
Category: Geo sciences & technology
Research persons: Professor E. Bruce Watson
Location: Rensselaer Polytechnic Institute (RPI), 110 8th St., Troy, NY 12180, United States
Details
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.
About Researchers:
E. Bruce Watson
Institute Professor, Experimental Geochemistry
Rensselaer Polytechnic Institute
Contact Information:
Phone: (518) 276-8838
Email: watsoe@rpi.edu
Web: www.rpi.edu/~watsoe
Education:
Ph.D., Massachusetts Institute of Technology
B.A., University of New Hampshire
Research Areas:
Experimental Geochemistry
Most Related Links:
http://www.eurekalert.org/pub_releases/2007-09/rpi-acr091807.php
http://www.asa3.org/weblog/jackhaas/2007/09/19/ArgonconclusionResearchersre.html
http://en.wikipedia.org/wiki/Earth's_atmosphere
http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/overview.html
http://www.lpod.org/ots/?cat=14
http://www.physorg.com/news109427299.html
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