miércoles, 5 de diciembre de 2012
New theory about the age of Grand Canyon
Over the years, scientists have taken a variety of approaches to determine the canyon's age, such as estimating how quickly sediment traveled from one end of the canyon to the other and studying the age of formations within the canyon. Some produced ages as young as 5 million to 6 million years for portions of the canyon, and others ages as old as 17 million years.
Science has recently published online a new theory which deals about a new theory of the age and origin of Grand Canyon in Colorado (Arizona). The study, carried out by Rebecca Flowers (University of Colorado) and Kenneth Farley (California Institute of Technology), has analyzed four rock samples from the western portions of the Grand Canyon and four from the eastern reaches of the gorge. The pattern of helium concentrations in the samples suggests that substantial parts of the western portion of the Grand Canyon were already carved to within a few hundred meters of their current depth by about 70 million years ago and that erosion hasn't increased dramatically in recent eras, the researchers report. That's a far cry from the 5-million-to 6-million-year-old age suggested by previous research, and is about quadruple the oldest previous estimate from other teams for the canyon's age.
Nevertheless, not everyone is convinced by the team's evidence. Karl Karlstrom, a structural geologist at the University of New Mexico, Albuquerque, describes the findings as "out in left field." His team has also analyzed helium concentrations in apatites that were collected just a couple of kilometers downstream from where Flowers and Farley collected their samples in the western Grand Canyon. And their preliminary results, Karlstrom says, bolster the notion of a young gorge. Those soon-to-be-published results suggest that those rocks were still between 50° and 60°C—implying that they were well over 1 kilometer below the surface of Earth's crust—between 15 million and 20 million years ago.
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Miquel Mir Gual