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News item - Grand Canyon began forming about 17M years ago

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  • Todd S. Greene
    UNM Researchers Discover Significantly Older Grand Canyon Western portion of canyon actually formed 17 million years ago by Steve Carr (University of New
    Message 1 of 1 , Apr 8, 2008
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      UNM Researchers Discover Significantly Older Grand Canyon
      Western portion of canyon actually formed 17 million years ago
      by Steve Carr
      (University of New Mexico press release, 3/13/2008)

      Up until recently, it was thought the Grand Canyon was approximately
      six million years old. That was until researchers in the Earth and
      Planetary Sciences Department in the College of Arts and Sciences at
      the University of New Mexico discovered otherwise. Using a technique
      called uranium-lead isotope (U-Pb) dating of water table-type
      speleothems or cave formations, researchers Victor Polyak, Carol Hill
      and Yemane Asmerom, were able to determine the western portion of the
      Grand Canyon actually began to form some 17 million years ago.

      That revelation, or "Eureka moment" as Asmerom called it, makes the
      Grand Canyon almost three times older than originally thought.

      The research, which began more than nine years ago, was funded by the
      National Science Foundation for $250,000 and published recently in the
      journal Science. The discovery was enabled by the realization that
      certain cave formations, such as mammillary coatings that form near
      groundwater tables, allowed researchers to date both parts of the
      canyon radiometrically accurately for the first time.

      "The fact that many Grand Canyon caves contain mammillary speleothems
      has allowed us to take advantage of advances in U-Pb and U-series
      analytical techniques in an effort to make the long sought chronology
      possible," said Polyak in the article.

      As it turned out, the caves and cave deposits, which are located
      throughout the Grand Canyon, were ideal in that the researchers found
      both pre-existing and chemical sediments deposited before, during and
      after the incision of the canyon.

      Naturally, the caves preserved and protected them from weathering.
      With sufficient uranium lead ratios and yield U-Pb dates, the
      mammillary coatings place the water table within the canyon at a
      particular place and at an absolute time. The mammillary coatings
      allow for the incision history of the Grand Canyon to be reconstructed.

      "We knew if we could successfully determine the age of these coatings,
      we could position a pre-existing water table at a certain place in the
      canyon at a particular time," said Polyak.

      The core data, which included 57 analyses, came from nine mammillary
      coatings from throughout the canyon, both east and west. The results
      from the eastern Grand Canyon displayed faster water table descent
      rates than data from the western Grand Canyon which showed stable,
      slow drops in the water table. The data showed a slower incision rate
      in the western portion than the eastern.

      The resulting data provided a record of water table deposits as the
      Colorado River cut through the canyon over millions and millions of
      years – approximately 17 million for the western portion.

      "Based on uranium-lead dates of these deposits and the positions of
      these deposits throughout the canyon, that the western Grand Canyon is
      much older than what most scientists have thought," said Polyak.

      "Normally what you'd expect is for the area around the headwaters to
      be older than what they call the 'tail of the river,' said Asmerom.
      "Here, essentially, you have a 10 million year old pre-history of the
      western Grand Canyon before the Colorado River became a though-flowing
      river to the Gulf of California."

      The research may provide further clues and could eventually offer the
      possibility for a reconstruction of the canyon's history.

      "These results were possible by the convergence of new technical
      capabilities achieved in our Radiogenic Isotope Laboratory, the
      conceptual breakthrough in connecting the mammillary to the water
      table and having samples that had sufficient uranium for dating," said
      Asmerom.

      For more information on the Radiogenic Isotope Laboratory at UNM
      visit: Radiogenic Isotope Laboratory.
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