Andrew Yee[_1_]
May 2nd 08, 11:17 PM
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
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