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Fw: {MPML} Oldest Known Impact Crater Found in Greenland

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  • Bruce Kamiat
    A list for asteroid and comet researcher ... From: mpml@yahoogroups.com To: mpml@yahoogroups.com Sent: Friday, June 29, 2012 5:51 AM Subject: {MPML} Digest
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      A list for asteroid and comet researcher



      ----- Original Message -----
      From: mpml@yahoogroups.com
      To: mpml@yahoogroups.com
      Sent: Friday, June 29, 2012 5:51 AM
      Subject: {MPML} Digest Number 4165


      A list for asteroid and comet researcher Group

      Oldest Known Impact Crater Found in Greenland
      Thu Jun 28, 2012 11:55 am (PDT) . Posted by: "Ron Baalke"
      http://www.cardiff.ac.uk/news/articles/oldest-known-impact-crater-found-9091.html

      Oldest known impact crater found
      Cardiff University
      28 June 2012

      A 100 kilometre-wide crater has been found in Greenland, the result of a
      massive asteroid or comet impact a billion years before any other known
      collision on Earth.

      The spectacular craters on the Moon formed from impacts with asteroids
      and comets between 3 and 4 billion years ago. The early Earth, with its
      far greater gravitational mass, must have experienced even more
      collisions at this time - but the evidence has been eroded away or
      covered by younger rocks. The previously oldest known crater on Earth
      formed 2 billion years ago and the chances of finding an even older
      impact were thought to be, literally, astronomically low.

      Now, a team of scientists from Cardiff, the Geological Survey of Denmark
      and Greenland (GEUS) in Copenhagen, Lund University in Sweden and the
      Institute of Planetary Science in Moscow has upset these odds. Following
      a detailed programme of fieldwork, funded by GEUS and the Danish
      'Carlsbergfondet' (Carlsberg Foundation), the team have discovered the
      remains of a giant 3 billion year old impact near the Maniitsoq region
      of West Greenland.

      "This single discovery means that we can study the effects of cratering
      on the Earth nearly a billion years further back in time than was
      possible before," according to Dr Iain McDonald of the School of Earth
      and Ocean Sciences, who was part of the team.

      Finding the evidence was made all the harder because there is no obvious
      bowl-shaped crater left to find. Over the 3 billion years since the
      impact, the land has been eroded down to expose deeper crust 25 km below
      the original surface. All external parts of the impact structure have
      been removed, but the effects of the intense impact shock wave
      penetrated deep into the crust - far deeper than at any other known
      crater - and these remain visible.

      However, because the effects of impact at these depths have never been
      observed before it has taken nearly three years of painstaking work to
      assemble all the key evidence. "The process was rather like a Sherlock
      Holmes story," said Dr McDonald. "We eliminated the impossible in terms
      of any conventional terrestrial processes, and were left with a giant
      impact as the only explanation for all of the facts."

      Only around 180 impact craters have ever been discovered on Earth and
      around 30% of them contain important natural resources of minerals or
      oil and gas. The largest and oldest known crater prior to this study,
      the 300 kilometre wide Vredefort crater in South Africa, is 2 billion
      years in age and heavily eroded.

      Dr McDonald added that "It has taken us nearly three years to convince
      our peers in the scientific community of this but the mining industry
      was far more receptive. A Canadian exploration company has been using
      the impact model to explore for deposits of nickel and platinum metals
      at Maniitsoq since the autumn of 2011."

      The international team was led by Adam A. Garde, senior research
      scientist at GEUS. The first scientific paper documenting the discovery
      has just been published in the journal "Earth and Planetary Science
      Letters".
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