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miercuri, 15 august 2012

New impact crater in the Canadian arctic revealed

Last week, NASA’s Curiosity Rover made its historic landing on Mars. And while scientists at the Jet Propulsion Laboratory in Pasadena California get ready to examine the environs of Gale crater, a new impact feature was revealed by researchers right here on Earth.

Two years ago, surveyors for the Natural Resources Canada Geo-Mapping for Energy and Minerals program noted an unusual geological feature on Victoria Island in the high Canadian Arctic. This 25 km-wide circular feature displayed signs of tilted strata, shatter cones, and fractured radial lines atypical of the region, but typical of a meteorite impact.

Last week, co-discovers Brian Pratt and Keith Dewing of the University of Saskatchewan and the Geological Survey of Canada published the find, stating that the crater was about 130 million to 350 million years old, which would place it from the late Paleozoic to the mid- Mesozoic era.

“Impact craters like this give us clues into how the Earth’s crust is recycled and the speed of erosion, and may be implicated in episodes of widespread extinction in the past.” Said Pratt, who has been visiting the remote site in the Northwest Territories for the past two summers.

Impact craters are common features on bodies such as the Moon and Mars, but rare on Earth. Terrestrial processes such as wind, ice and rain erosion make short work of craters and only about 160 have been identified worldwide. Dubbed the Prince Albert impact crater after the peninsula that it is located on, this crater is the 30th “astrobleme” identified in Canada. Another famous crater in Barringer Meteorite Crater near Flagstaff, Arizona, and meteorite craters have even been found in the Australian Outback by devoted amateurs scouring Google Earth.

The Chicxulub impact off of the Yucatan peninsula is thought to have been the “smoking gun” that wiped out the dinosaurs 65 million years ago, and another more recent impact in North America 12,900 years ago during the Younger Dryas is thought to be a precursor to a more recent mass extinction. The Prince Albert impactor would have had to have been at least a kilometre in size and have released in the equivalent of over 50,000 megatons of TNT when it hit.

Several new impact features where discovered with the advent of aerial photography in the early 20th century. Many are now filled-in lakes that have been further eroded by subsequent glacial sheets which began receding during the end of the last Ice Age 18,000 years ago.

Pratt further notes that it’s amazing that the feature remained hidden for so long. “Several geologists visited the era in the ‘60s & ‘70s,” Pratt said; “It was those old industry reports… that had us intrigued.”

Features such as the Prince Albert crater can be dated by the amount of erosion they have sustained and correlating subsequent activity known as Superpositioning. These sorts of features remind us that the solar system is a busy and dangerous place, and several astronomical surveys such as Pan-STARRS and the LINEAR survey near Apache Point in New Mexico exist to hunt for the next big Earth threatening comet or asteroid.

Although statistically rare, an “extinction level event” is inevitable on geologic timescales. Various grass-roots organizations such as the B612 committee chaired by former Apollo astronaut Rusty Schweickart exist dedicated to providing a think-tank for how to deflect such threatening space rocks.

When is the next Earth impactor due? What other prehistoric impact features exist out there, awaiting discovery? One thing is for certain; it’s a dangerous universe, as research both on other worlds and our own backyard has revealed.

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