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Science Forum Index » Astro Forum » Florida State U. geochemist challenges key theory regarding Earth's formation (Forwarded)
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| Andrew Yee |
 Posted: Fri May 02, 2008 5:25 pm |
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University Communications
Florida State University
Tallahassee, Florida
CONTACT:
Munir Humayun, (850) 644-1908
May 1, 2008
FSU geochemist challenges key theory regarding earth's formation
By Barry Ray
TALLAHASSEE, Fla. -- Working with colleagues from NASA, a Florida State
University researcher has published a paper that calls into question three
decades of conventional wisdom regarding some of the physical processes
that helped shape the Earth as we know it today.
Munir Humayun, an associate professor in FSU's Department of Geological
Sciences and a researcher at the National High Magnetic Field Laboratory,
co-authored a paper, "Partitioning of Palladium at High Pressures and
Temperatures During Core Formation," that was recently published in the
peer-reviewed science journal Nature Geoscience. The paper provides a
direct challenge to the popular "late veneer hypothesis," a theory which
suggests that all of our water, as well as several so-called "iron-loving"
elements, were added to the Earth late in its formation by impacts with
icy comets, meteorites and other passing objects.
"For 30 years, the late-veneer hypothesis has been the dominant paradigm
for understanding Earth's early history, and our ultimate origins,"
Humayun said. "Now, with our latest research, we're suggesting that the
late-veneer hypothesis may not be the only way of explaining the presence
of certain elements in the Earth's crust and mantle."
To illustrate his point, Humayun points to what is known about the Earth's
composition.
"We know that the Earth has an iron-rich core that accounts for about
one-third of its total mass," he said. "Surrounding this core is a rocky
mantle that accounts for most of the remaining two-thirds," with the thin
crust of the Earth's surface making up the rest.
"According to the late-veneer hypothesis, most of the original
iron-loving, or siderophile, elements" -- those elements such as gold,
platinum, palladium and iridium that bond most readily with iron -- "would
have been drawn down to the core over tens of millions of years and
thereby removed from the Earth's crust and mantle. The amounts of
siderophile elements that we see today, then, would have been supplied
after the core was formed by later meteorite bombardment. This bombardment
also would have brought in water, carbon and other materials essential for
life, the oceans and the atmosphere."
To test the hypothesis, Humayun and his NASA colleagues -- Kevin Righter
and Lisa Danielson -- conducted experiments at Johnson Space Center in
Houston and the National High Magnetic Field Laboratory in Tallahassee. At
the Johnson Space Center, Righter and Danielson used a massive 880-ton
press to expose samples of rock containing palladium -- a metal commonly
used in catalytic converters -- to extremes of heat and temperature equal
to those found more than 300 miles inside the Earth. The samples were then
brought to the magnet lab, where Humayun used a highly sensitive
analytical tool known as an inductively coupled plasma mass spectrometer,
or ICP-MS, to measure the distribution of palladium within the sample.
"At the highest pressures and temperatures, our experiments found
palladium in the same relative proportions between rock and metal as is
observed in the natural world," Humayun said. "Put another way, the
distribution of palladium and other siderophile elements in the Earth's
mantle can be explained by means other than millions of years of meteorite
bombardment."
The potential ramifications of his team's research are significant,
Humayun said.
"This work will have important consequences for geologists' thinking about
core formation, the core's present relation to the mantle, and the
bombardment history of the early Earth," he said. "It also could lead us
to rethink the origins of life on our planet."
The researchers' Nature Geoscience paper is available for purchase or via
subscription at
http://www.nature.com/ngeo/journal/vaop/ncurrent/index.html#le |
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