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Geotimes
 Published by the American Geological Institute
November 2000
Newsmagazine of the Earth Sciences

News Notes


FIELD NOTES
 
Peeking into planetary past

On Jan. 18, 2000, a meteorite blazed through the night sky and landed on the frozen surface of Tagish Lake near the Yukon-British Columbia border in Canada. One week later, several fragments were removed from the icy lake. Analyses have revealed the meteorite, now called the Tagish Lake meteorite, is a new type of carbonaceous chondrite that also appears to be the least altered meteorite ever found on Earth.
 
“It’s the best snapshot we have of the bulk chemical composition of the early solar nebula,” Peter Brown of the University of Western Ontario says. Because the meteorite has experienced little thermal or aqueous alteration, its composition is the best analogue scientists have to study how particles in the solar system originally condensed. 
 
Some of the meteorite’s components even pre-date the solar system. The Tagish Lake meteorite contains some of the most pristine pre-solar grains known to exist on Earth. Also known as interstellar grains, these crystals are small, refractory grains generated when a supernova explodes or in the cooling atmosphere of a giant star. They are the only tangible source of information we have on Earth for learning about the nucleation of stars. 
 
Brown and his colleagues published their findings in the Oct. 13 Science. “We are in the delightful position of knowing that most of the interesting things we can learn from Tagish Lake [meteorite] have yet to come,” Brown says.              

Laura Wright


The interstellar grains found on the Tagish 
Lake meteorite might provide insight into the 
evolution of stars such as the young and 
violently erupting, super-hot star shown in this
image taken by Hubble’s Wide Field Planetary
Camera 2 in March 1997.  Photo courtesy of NASA.
 


Noah's village

Undersea explorer Robert Ballard has found remnants of a civilization buried along the ancient shoreline of the Black Sea. The find supports the hypothesis linking the catastrophic flood that inundated the Black Sea, which was a freshwater lake about 7,000 years ago, to the biblical story of Noah and the flood in the Babylonian story of Gilgamesh. William Ryan and Walter Pitman III, of Columbia University’s Lamont-Doherty Earth Observatory, first suggested the idea three years ago in their book, Noah’s Flood. But missing from their story was direct evidence of a flooded ancient city from that time. On Sept. 12, Ballard reported the discovery of a rectangular area about 12 feet by 45 feet with carved wooden beams, branches and stone tools collapsed in the mud matrix. Pieces of ceramics at a second site seven miles away suggest another inhabited area. National Geographic Society and others sponsored the expedition to map northern Turkey’s coastline using sonar equipment. Undersea robots zeroed in on 200 square miles of what would have been prime beachfront property when the Black Sea was still fresh water.

Christina Reed



 
 
Shaking Alaska

Seismic profiling has revealed approximately 30 blind, transpressional faults running through Cook Inlet in south-central Alaska, in addition to the exposed Castle Mountain fault that has been known to be active since the 1960s. Peter Haeussler of the U.S. Geological Survey in Anchorage believes these faults were formed only in the past 1.5 million years and are active today. Over the past 15 to 20 million years, the Yakutat tectonic block has been pushing against the coast of Alaska, essentially “squirting part of the fore arc to the southwest,” Haeussler says.

Alaskans haven’t had to worry about a major earthquake in the region for several decades. The magnitude-9.2 Good Friday earthquake that devastated the region in 1964 was a subduction-type earthquake with a 700-year recurrence interval.  While Alaskans won’t experience another one of those for a long time, they might have to deal with large earthquakes originating in the fault zone just below the surface of Cook Inlet. 
 
The only known historical earthquake originating in Cook Inlet was a magnitude-6.9 event that occurred on April 26, 1933. Haeussler believes that another big event will occur, and while he is not making any predictions, he worries about the oil pipelines that run through the region. “Pipelines in the Cook Inlet ought to be built to take at least a meter or so of offset,” Haeussler says. If an earthquake were to cause a crack in the pipeline, significant environmental damage could occur. “Cook Inlet is commonly very windy, it has fast tides, and in the winter there are up to 40-acre sheets of ice that flow in and out of the inlet,” he says. “It would be very difficult to clean up and oil spill there.”                                                        

Laura Wright



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