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Impact |
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| Studying a kaolin mine, UGA scientists identify layer of material ejected from Chesapeake Bay meteor strike | |||
| By Phil Williams |
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People in Georgia’s
Dodge and Bleckley counties have for years picked up small pieces
of natural glass called “Georgiaites” which were produced
by an unknown
Now UGA researchers studying a kaolin mine in Warren County have found a layer of small grains which indicate both the grains and the Georgiaites were products of a recently discovered impact that left a huge crater beneath the waters of Chesapeake Bay. “We knew we had these tektites here, but we’d never found them in place,” says Michael Roden, a geologist and part of the research team. “We believe this layer is further evidence that the Chesapeake Bay impact was an enormous event with widespread consequences.” The research was published in the August issue of the journal Geology. The work was spearheaded by UGA graduate student Scott Harris (now with Brown University) in collaboration with Roden, UGA geologists Paul Schroeder and Steven Holland, and Ed Albin of the Fernbank Museum and Mack Duncan of J.M. Huber Corporation. Tektites are brown to green glassy objects, generally small and rounded, that are thought to be of extraterrestrial origin. The only other state in the United States where tektites have been found in abundance is Texas. Some 1,700 have been found in Georgia to date, and potassium-argon geochronology has dated them to around 35 million years of age. The Chesapeake Bay impact crater was only discovered about a decade ago. Before this current discovery of tektites, no deposition layer from the impact had been found. It was unclear whether Georgiaites had resulted from the cataclysmic collision of the Chesapeake Bay bolide with the Earth. (“Bolide” is a generic term for an impacting body.) The now-unused kaolin mine in Warren County where the discovery was made was near the sea’s edge in ancient times. This former shore, now across the central part of Georgia, is more or less coincident with the fall line. The impact in the Chesapeake Bay clearly caused a huge amount of material, both from the Earth and from the asteroid, to become airborne, and the layer of tektites—discovered at a depth of 25 feet in the kaolin mine—was probably laid down by that event. It was an active time: In the period between 34 million and 37 million years ago, at least five comets or asteroids collided with Earth. Since some of those impacts may have caused climate alterations and at least regional disruptions of ecosystems, knowing more about the ejecta from the impacts is important. The layer the scientists identified is perhaps the most easily accessible, undisturbed layer of materials that probably came from the Chesapeake Bay impact and can therefore add knowledge about that event. The search for the layer, led by Harris, led to the discovery of so-called shocked quartz—grains whose physical “thumbprint” mark them as having originated from the extremely high pressures characteristic of an impact event. Just how big the explosion was when this celestial visitor hit the Earth is unclear, but Roden says it was many times bigger than such events as the explosions of Mt. St. Helen’s or even Krakatoa. |
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