Geotimes Logo NEWS NOTES  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



 

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