Using Satellites to Unearth Fossils   Page 2

Each year the winds and harsh winters of the Gobi peel away additional layers of the red sandstone at Ukhaa Tolgod, exposing more fossils. Every summer since 1993 researchers from the museum have traveled back to the site, and they've continued to find remarkable specimens. Despite their success, the paleontologists still believe that there may be undiscovered sites just as good or even better in other parts of the desert. So when Novacek and his team make their yearly pilgrimage, they also take time to search for new fossil beds.
 

  Fossil Gallery

In general, the fossil-bearing red sandstone can be found in bluffs and outcrops of eroded sedimentary rock. After the scientists locate a potential site either by chance, by map, or by word of mouth, they go to the area and poke around until they see enough evidence of good fossils to start digging. "But locating these sites is often very difficult," says Novacek. They are dispersed across the vast desert and topographic and geologic maps of the Gobi aren't always accurate. Novacek explains that driving around the Gobi looking for sites that may or may not be there isn’t always the best idea. Hundred-degree temperatures and sandstorms are common in the Gobi. There are no gas stations or super markets along the way, so the scientists have to bring large, unwieldy supply and gas trucks with them. Once, while heading for a site they knew existed in the western Gobi, the team had to go off road. They got mired in a large expanse of sand and had to dig out the supply trucks and gas tanker twenty-one times in one day. "I want to know exactly where we are going before I take a column down there," said Novacek.
 

   

In order to find new sites and pinpoint ones they know exist, Novacek and the other fossil hunters at the American Museum of Natural History started using images of the Gobi Desert retrieved from the Landsat 5 satellite. This satellite, launched by NASA in 1984, moves in a near-circular orbit very nearly from pole-to-pole around the Earth and scans strip after strip of our spinning planet. A sensor array onboard known as the Thematic Mapper has seven different types of detectors, which acquire images of different wavelengths of reflected sunlight or emitted thermal radiation from the surface of the Earth. One light detector records only the blue light coming off the Earth (band 1), another observes all the yellow-green light (band 2), and still another picks up on thermal radiation (band 7). These data are then beamed back to the planet's surface where they can be made into detailed images of the Earth's surface. Scientists can mix and match the various bands into a single image to highlight various aspects of a section of land. For instance, vegetation in a region can be highlighted by combining the blue, near-infrared, and red bands of the Thematic Mapper data. (View a comparison between true color and infrared false color Landsat data.)
 

 

True Color
Landsat Image
This true color Landsat 5 image of the Gobi desert covers an area between Ukhaa Tolgod and the Flaming Cliffs, two of Mongolia's most famous fossil sites. Landsat data are more accurate than existing maps of the region, so they are extremely helpful in the search for fossils.

Unfortunately, there is no simple combination of bands that will immediately pinpoint the fossil sites in the Gobi. Novacek explains that the best they can do is combine blue, near-infrared, and thermal radiation bands on the images of the desert. Together these bands show the rock formations of the Gobi in the most detail. "We then look for the outcrops with the right features and contours," he says. After years of dealing with the geology of the Gobi, Novacek and his team have developed a sense for what types of rock formations will yield fossils and how to spot them on an image. Though there are no hard and fast rules for identifying fossil-bearing outcrops, he explains they are usually found at the base of the larger mountains that run through the Gobi. These outcrops also contain layers of sedimentary rock, and they are well-weathered, low-lying, and sparsely vegetated. All of these aspects can be detected in the satellite images.

So far, Novacek says they have had some success using these Landsat images. Last year, in fact, they tracked down one such site northeast of Ukhaa Tolgod and visited it on their yearly campaign. While it was nothing like Ukhaa Tolgod, he says they did find a few well-preserved, fossilized mammal skulls as well as some partial fossils of dinosaurs. The find gives him confidence that in the future the maps will be useful in tracking down both new sites as well as confirming sites shown on the questionable older maps of the Gobi. "And more than anything they will save us many days of driving across the desert," he says.

References
Loope, D. B., L. Dingus, C. C. Swisher, and C. Minjin, 1998: Life and death in a late Cretaceous dune field, Nemegt Basin, Mongolia, Geology, 26(1), pp. 27-30.

Norell, M. A., J. M. Clark, L. M. Chiappe, and D. Dashzeveg, 1995: A Nesting Dinosaur, Nature, 378, 21/28 December, pp. 774-776.

Webster, D., 1997: Dinosaurs of the Gobi: Unearthing a fossil trove, National Geographic, July 1996, pp. 73-89.

Links
The American Museum of Natural History

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Band Combination
This image uses Landsat band 7 (shortwave infrared) for red, band 4 (near infrared) for green, and band 1 (blue) for blue. Vegetation and different types of rock and soil stand out much more clearly in this image, enabling fossil hunters to find likely fossil sites. (View a comparison between true color and infrared false color Landsat data.) (Images by Barbara Summey, NASA GSFC Visualization Analysis Lab, based on Landsat 5 data provided by the Laboratory for Terrestrial Physics)

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