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NEWS NOTES |
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July 1999 |
How dinosaurs walked the walk
Martian past may include plate tectonics
Geoscientists active on Capitol Hill
Could the ocean store excess CO2?
How dinosaurs walked the walk
Stephen M. Gatesy of Brown University is an evolutionary biologist who
was not looking for dinosaur tracks when he visited the Fleming Fjord Formation
in East Greenland in 1988. But while he was looking for mammal bones, he
stumbled upon some Late Triassic dinosaur footprints.
"We were literally just walking down a hillside, and then
we were standing on footprints," he says, remembering the day he and colleagues
Neil H. Shubin (University of Pennsylvania) and Farish A. Jenkins Jr. (Harvard
University) found the tracks. They were too interesting not to study. Unlike
many ichnologists, Gatesy says, he and his fellow biologists studied the
footprints from the perspective of limb function.
Gatesy and his colleagues published work in the May 13,
1999, Nature, interpreting the Greenland footprints as three-dimensional
records of the foot and limb movements of Triassic theropod dinosaurs.
Shallow prints, like casts, preserve the imprints of feet.
But many of these prints were sloppy, elongated, and distorted. Gatesy
and his colleagues eventually realized that the prints weren't exact representations
of the bottoms of the dinosaurs' feet. Instead, they recorded motion. "The
deeper you sink, the more motion you get," Gatesy explains.
"Most people have been content to find weird tracks ...
and put a name on them and then dismiss them," says Kevin Padian of the
Museum of Paleontology at the University of California-Berkeley. "But tracks
like that often show you how an animal is moving in sloppy sediment." In
the same issue of Nature, Padian writes that Gatesy and his colleagues
discovered tracks others might have ignored simply because they were indistinct.
Instead, Padian says, the biologists "turned the find into a model for
future work."
The tracks were unusually sloppy looking, Gatesy remembers.
"When I first found them, I couldn't even tell which direction the animal
was going." Most likely the dinosaurs were walking through mud on the shore
of a rift lake, and their feet sank with each step. The result was elongated
prints of varying widths and toe patterns.
When they first discovered the prints, the researchers
classified them into discrete categories. But after the team sent a turkey
walking through mud, they saw that the turkey's prints were similar to
the Greenland tracks. They realized the Greenland prints recorded a whole
continuum of motion, rather than classifiable imprints of foot patterns.
The sloppiness of the substrate preserved the "entry and exit wounds" the
foot made as the dinosaur walked, the authors write.
As a dinosaur stepped into the mud, its toes sank. As
it moved forward and moved its toes back out of the mud, part of the movement
occurred beneath the surface and its toes displaced subsurface mud. The
laminae are still displaced in the rock from that motion, Gatesy says.
The team has cut the rock and studied cross sections to model and simulate
the three-dimensional motion.
Overall, the team found that the Triassic theropod prints
are similar to the prints of modern ground-dwelling birds, but that they
also demonstrate significant functional differences in foot posture, in
the position of the first toe (the hallux), and in how high the animals
carry their heels. "We see aspects that are common to both [the theropods
and modern birds] but also some differences that developed along the way,"
Gatesy says. Comparing the locomotor patterns helped the researchers make
determinations about evolution.
For example, Gatesy's team found that modern birds inherited
some locomotor techniques from the theropods. Bird and dinosaur tracks
have often been distinguished based on the imprint of the hallux, Padian
says. The Greenland prints showed the hallux entering the mud as a bird's
would, but then disappearing upon exit. They determined that this change
didn't reflect any imprint of the hallux, but reflected a change in motion:
the animal brought its toes together as it lifted its foot out of the mud.
After they ran turkey and guineafowl through muddy, sloppy sediments, they
found that modern birds had inherited this locomotor trait, Padian says.
The team's first models were hand-made. Gatesy says they
used coat hangers, wires, playdough, clay, and mud to find out what kind
of motion, in what kind of substrate, would create such prints. "We tried
anything to figure out the basic geometries," Gatesy says. Now the team
is developing a computer model that will simulate the three-dimensional
movement of each foot through the muddy substrate.
The researchers plan to use a CAT scan to see into the
rock and study the minute displacements the dinosaur toes left as each
foot moved beneath the surface. These data will help them reconstruct each
foot's three-dimensional path.
- Kristina Bartlett
Geotimes
Martian past may include plate tectonics
In our solar system, only Earth appears to possess active plate tectonics.
However, new data retrieved by the Mars Global Surveyor (MGS) suggests
that, over four billion years ago, the Red Planet may also have undergone
plate tectonic processes.
The April 30, 1999, issue of Science features a
pair of articles presenting magnetic field measurements for the martian
crust. This research, conducted by M.H. Acuña and J.E.P. Connerney
of NASA Goddard Space Flight Center, as well as scientists from the United
States and France, reveals bands of strongly magnetized crust trending
east-west on Mars. The investigators suggest that the bands are evidence
for ancient martian rifting similar to sea-floor spreading on Earth.
While passing unusually close to the martian surface during
orbit adjustment maneuvers (at times within 100 km), the MGS magnetometer
experiment obtained its highest-resolution images of surface magnetic fields.
The magnetometer data revealed intense magnetic sources, most in the planet's
southern hemisphere. "We've sampled much of the terrain and have a pretty
good sense of where the crustal magnetism is," Connerney says. Magnetic
striping also appears in a northern area near Acidalia Planitia, where
multiple bands exist for researchers to model, Connerney says.
The linear magnetic bands are generally hundreds of kilometers
long, with the longest band stretching more than 2,000 kilometers. The
most intense magnetism detected lies in the Terra Sirenum region of Mars.
The total magnetic field intensity in the region exceeds 1,600 nanoteslas
at an approximately 100-kilometer altitude, and the estimated net magnetic
moment for one stripe within the region is approximately 1.3x1017 amperes
per square meter. Even Earth's largest magnetic anomalies pale in comparison.
For example, the Kursk anomaly in Russia has a magnetic moment an order
of magnitude lower than that of Terra Sirenum, Connerney says.
The strength of the magnetic anomalies isn't the only
evidence the researchers cite for martian plate tectonics. Adjacent magnetic
bands on the planet generally have opposite magnetic polarities, similar
to the magnetic stripes on Earth's sea floor.
On Earth, the alternating polarities of magnetic stripes reflect
the influence of episodic reversals of the planet's magnetic poles. The
reversing magnetism is superimposed upon certain minerals, such as magnetite,
that form in the continuously extruded lava of spreading centers and rift
zones. The lava spreads somewhat symmetrically on opposite sides of the
rift, creating bands of magnetized rock that lie almost parallel to each
other and their sources. The magnetic pole reversals are driven by the
magnetic dynamo induced by Earth's molten outer core. Mars Pathfinder
revealed a martian core of approximately 1,000 kilometers in diameter,
although it may no longer be molten. However, if the martian bands indicate
reversing magnetic polarities and continuously extruded magma, then the
new research may suggest that Mars once had an active internal magnetic
dynamo in its core and underwent active plate tectonics.
So far, only a few alternative explanations for the magnetic
bands have received substantial support, in part, Connerney says, because
they require evidence of astounding magnetism. "No matter how you look
at it, we need huge volumes of very magnetic stuff," he says. Without plate
tectonics as an explanation, Connerney suggests, "it's hard to imagine
extruding 200 kilometers width of intrusive [rock] into a crack ... and
doing that several times in parallel. I'm guessing that if it isn't crustal
spreading, it will be something nobody's thought of yet. Something without
an easy Earth analog to guide interpretation."
However, in one NASA press release, Acuña presents
an alternative hypothesis based on the fracturing of a uniformly magnetized
crust. "Imagine a thin coat of dried paint on a balloon, where the paint
is the crust of Mars," Acuña says. "If we inflate the balloon further,
cracks can develop in the paint, and the edges of the cracks will automatically
have opposite polarities, because nature does not allow there to be a positive
pole without a negative counterpart."
Hap McSween of the University of Tennessee-Knoxville recognizes
that the new data can be evidence for extension of the martian crust. He
says, however, that for now he is reserving judgment about evidence for
plate tectonics. "Even though there isn't a symmetrical pattern ... some
kind of extensional tectonics with volcanism filling these rifts does provide
an acceptable explanation, a plausible explanation for how you would get
this pattern of alternating magnetic polarity. But it would've been more
convincing if they had found a center of symmetry; an axis that is bordered
by some symmetrical stripes."
The martian bands have been exposed for four billion years.
McSween suggests that any evidence of a center of symmetry may have been
erased; Acuña, Connerney, and their colleagues have proposed the
same idea. "The compressional evidence may have been destroyed, maybe covered
over by later volcanism," McSween says. The other researchers add that
meteorite bombardments might also have erased some evidence.
The discovery of magnetic banding on Mars is still in
its infancy, and the data are relatively scarce. "Of course, we'd like
more uniform sampling, and we'd love to get closer to the surface, but
that's another mission," Connerney says. "For now, we'll have to be content
to go through the existing data carefully, model the crustal magnetism
a bit better, [and] do some detailed modeling in other areas."
- Joshua A. Chamot
Department of Geology,
University of Tennessee, Knoxville
Geoscientists active on Capitol Hill
Springtime in Washington brought not only cherry blossoms and warm weather,
but also a flurry of geoscientists to Capitol Hill. In April, 14 geoscientists
met with members of Congress and their staffs as part of the annual Congressional
Visits Day, hosted by the science and engineering community. In May, the
American Geological Institute (AGI) joined with the American Geophysical
Union to sponsor a seismology demonstration at the Coalition for National
Science Funding exhibition of research funded by the National Science Foundation.
Both events aimed to show policy-makers the importance of investing in
research and development.
Convincing Congress that geoscience research should be
a funding priority is a continuing challenge. To make it happen, the strong
geoscience presence on Capitol Hill this spring must be followed by ongoing
outreach efforts.
Congressional Visits Day
More than 200 scientists and engineers congregated in Washington, D.C.,
on April 21 and
22 for the fourth annual Congressional Visits Day (CVD), sponsored
by the Science-Engineering-Technology Work Group and the Coalition for
Technology Partnerships. The day before they visited senators and representatives,
the scientists were briefed by members of the administration, including
Assistant to the President for Science and Technology Neal Lane, who thanked
participants and said their visits are invaluable and "generate continued
bipartisan support for research and development."
National Science Foundation Director Rita Colwell and
NASA Administrator Dan Goldin were among the agency leaders who provided
an overview of the President's budget request for science and technology.
They emphasized the tight budget environment created by caps on discretionary
spending in the 1997 balanced budget agreement. The speakers noted, however,
that science and technology are a priority. They cited increases in the
Presi-dent's FY 2000 budget request as a demonstration of the President's
commitment to science.
Also, House Technology Subcommittee Chair Connie Morella
(R-Md.) stressed the importance of partnerships. She emphasized the need
for the science and technology community to speak with a unified voice
and instructed them to follow a lesson learned in kindergarten: Hold hands,
watch out for traffic, and stick together. House Science Com-mittee Chair
James Sensenbrenner (R-Wisc.) continued this theme at a breakfast meeting
the following day, urging participants to "work together to make science
funding a priority."
Scientists participating with AGI paid more than 20 visits
to senators, representatives, and committee offices to discuss the importance
of investing in geoscience research and partnerships. They met with members
from South Carolina, Texas, Oklahoma, Pennsylvania, New Jersey, Colorado,
and Virginia. Attending for the second year, AGI Government Affairs Program
Committee Chairman Murray Hitzman remarked, "It is critical for geoscientists
to become involved in the political process, and this event represents
a positive first step."
Congressional Visits Day also featured an awards ceremony
for three members of Congress. The CVD sponsors presented Rep. George Brown
(D-Calif.), Sen. Pete Domenici (R-N.M.), and Sen. Joseph Lieberman (D-Conn.)
with lifetime leadership awards for their career-long efforts in support
of science and technology.
Showcasing geoscience research
Earthquake and seismology research were the focus of an exhibit cosponsored
by AGI
and the American Geophysical Union (AGU) at another Capitol Hill event
on May 19. The exhibit was one of 30 displays highlighting current research
sponsored by the National Science Foundation (NSF). Organized by the Coalition
for National Science Funding, this display of geoscience research aims
to show members of Congress NSF's role in meeting the nation's research
and educational needs.
The AGI-AGU exhibit showcased the work of the Incorporated
Research Institutions for Seismology (IRIS), a consortium of 91 universities
having research programs in seismology. Supported by the NSF and the U.S.
Geological Survey (USGS), IRIS maintains a worldwide system for monitoring
earthquakes and other powerful seismic events, such as nuclear tests, in
near-real time. Rick Aster, associate professor of geophysics at the New
Mexico Institute of Mining and Technology, illustrated current technology
with an exhibit featuring a working seismograph that allowed participants
to walk and jump and create and record their own earthquakes.
The AGI-AGU seismology exhibit was particularly timely
because the House recently passed the 1999 Earthquake Hazards Reduction
Authorization Act. The bill authorizes a total of $469.6 million over five
years for the National Earthquake Hazard Reduction Program (NEHRP), which
includes earthquake-preparedness projects at four participating agencies:
USGS, NSF, Federal Emergency Management Agency, and National Institute
of Standards and Technology. The bill also authorizes five years of funding
for a major new initiative that would modernize the USGS earthquake-monitoring
systems. Although the bill passed the House overwhelmingly, many have warned
that the tight budget climate may make it difficult for this authorization
to translate into actual money during the appropriations process.
Barbara Tewksbury, professor of geology at Hamilton College,
represented the National Association of Geoscience Teachers (NAGT) at its
booth, which focused on NAGT's programs for improving undergraduate geoscience
education. Other geoscience-related exhibits included "The Soil Record
of Past Climates and Atmospheres" by the University of Tennessee, "The
Virtual Earth System" by the University Corporation for Atmospheric Research,
and "Measuring the Earth with Quasars" by the American Astronomical Society.
- Kasey Shewey White
AGI Government Affairs Program
Could the ocean store excess CO2?
Most of the greenhouse gases, especially carbon dioxide, end up in the
atmosphere. At the same time, recent research shows that the atmosphere
is the smallest possible reservoir for CO2, compared to the
earth or to the ocean, and that this reservoir is quickly becoming saturated
with the greenhouse gas.
A hot topic in the issue of greenhouse gases is carbon
sequestration, the process of capturing carbon dioxide emitted from combustion
of fossil fuels and then storing it so that it doesn't enter the atmosphere.
Recent discussion of carbon sequestration has turned to the deep ocean
as a storage reservoir. During the Fourth International Conference on Greenhouse
Gas Control Technologies last year, Robert Kripowicz, U.S. Principal Deputy
Assistant for Fossil Energy, reported that the ocean contains about 40,000
gigatons of carbon dioxide in solution. "The 3.5 gigatons of net emissions
currently released annually worldwide is, both literally and figuratively,
a 'drop in the bucket,'" Kripowicz said.
One of the many questions surrounding the proposal to
store carbon in the ocean is: What will actually happen if carbon dioxide
is injected into the ocean? To answer this question, ocean chemist Peter
Brewer and his colleagues at Monterey Bay Aquarium Research Institute and
Stanford University left the lab and went directly into the ocean to watch
how liquid CO2 would behave when injected into the cold, high-pressure
environment of the deep sea.
"I realized that no one had done an experiment in the
deep ocean," says Brewer, a chemist who has worked 20 years studying oceanic
carbon dioxide. Brewer used a tool many oceanographers are turning to:
manned deep-sea submersibles. His team used the Monterey Bay Aquarium Research
Institute's deep-sea vehicles to inject liquid CO2 into five
sites off the shore of California. They published their results in the
May 7, 1999, Science.
The sites were at depths ranging from 349 meters to 3,627
meters. The scientists used the remotely operated vehicle Tiburon
to reach the greatest depth, where they placed a beaker of CO2 on
the ocean floor to see what would happen. To their surprise, the liquid
CO2 reacted rapidly with the seawater, forming a gas hydrate
at the bottom of the beaker and expanding the volume of CO2
until it spilled over the beaker's edge as gaseous globules. These hydrate-coated
globules of CO2 floated along the sea floor without penetrating
the sediment.
"We did not stay down long enough to observe the fate
of our material at 3,600 meters, but we hope to obtain time lapse imagery
next year," Brewer says. The researchers predict that, based on chemical
thermal dynamics and their field observations, the CO2 will
be released slowly from the hydrate. (Field work conducted by James J.
Morgan of the California Institute of Technology and Izuo Aya of Japan's
Ship Research Institute also confirms this prediction, Brewer adds). "But
we do not have field data, and one of our goals is to gain further knowledge
of this in the real world and with well-formed material," he says.
Could CO2 be stored in the ocean permanently?
Brewer's team reports in Science that such a goal is unrealistic.
"The idea of 'permanent' can mean different things," Brewer says. "To some
it may mean time scales well over 1,000 years, and we do not think this
is possible." At the same time, his team writes that residence times of
many hundreds of years may be realistic.
The idea of disposing of excess atmospheric carbon dioxide
in the ocean is gaining international strength with the recent adoption
of the 1997 Kyoto Protocols to United Nations Framework Convention on Climate
Change. The ocean's natural carbon buffering system could allow the deep
ocean to absorb the amount of carbon that would cause a doubling in atmospheric
concentration, while changing the ocean's carbon concentration by only
2 percent.
The U.S. Department of Energy released a report in April
that sets priorities and direction for research and technology development
of carbon sequestration. Sequestering the CO2 in the oceans
is one of the key research needs the report identifies, along with technologies
for capturing and separating CO2 from energy systems and storing
it in geological formations and terrestrial ecosystems (such as forests,
vegetation, soils, and crops).
The Intergovernmental Panel on Climate Change forecasts
that, under current conditions, global emission of carbon dioxide could
triple over the coming century, while concentrations of carbon dioxide
in Earth's atmosphere could double by the middleof the 21st century and
continue to accumulate.
- Kristina Bartlett
Geotimes
