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Boltysh crater

2007 Schools Wikipedia Selection. Related subjects: European Geography

   Location of the Boltysh Crater
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   Location of the Boltysh Crater

   The Boltysh Crater is an impact crater ( astrobleme) in Ukraine. It is
   24 km in diameter and its age is estimated to be 65.17±0.64 million
   years. This age is almost exactly the same as that of the Chicxulub
   Crater in Mexico, and the KT boundary. The Chicxulub impact is believed
   to have caused the mass extinction at the end of the Cretaceous era,
   which included the extinction of the dinosaurs.

   As well as Boltysh, the United Kingdom's Silverpit crater and several
   other craters around the world have estimated ages of about 65 million
   years, leading to the suggestion that the Earth was struck by multiple
   impactors at that time. The collision of Comet Shoemaker-Levy 9 with
   Jupiter in 1994 showed that such multiple impacts over a few days are
   possible.

Overview

   The Boltysh Crater is located in central Ukraine, in the basin of the
   Tyasmin River, a tributary of the Dnieper River. It is 24 km in
   diameter, and is surrounded by an ejecta blanket of breccia covering an
   area of 6500 km². It is estimated that immediately after the impact,
   ejecta covered an area of 25,000 km² to a depth of 1 m or greater, and
   was some 600 m deep at the crater rim.

   The crater contains a central uplift about 6 km in diameter, rising
   about 550 m above the base level of the crater. It currently lies
   beneath about 500 m of sediment deposited since the impact, and was
   discovered in the 1960s during prospecting for oil in the region.

Age

   When it was first identified, the age of the crater could only be
   roughly established. Sediments from the Cenomanian (98.9 to 93.5
   million years ago) and Turonian (93.5 to 89 million years ago) epochs
   were found beneath ejecta from the impact, thus setting an upper limit
   of about 89 million years on the age. Bore samples taken from sediments
   overlying the crater contain many fossils, and analysis of these dates
   the sediments at the Paleocene epoch, 65 to 54.8 million years ago. The
   age of the crater was thus constrained to between 54.8 and 98.9 million
   years.

   Later radiometric dating constrained the age further. The concentration
   of Uranium-238 decay products in impact glasses from the crater was
   used to derive an age of 65.04±1.10 million years, the first indication
   that it was of similar age to the Chicxulub Crater. Analysis of Argon
   radioactive decay products yielded an age of 65.17±0.64 million years.

Likelihood of multiple impact

   Although the ages derived for Chicxulub and Boltysh are the same to
   within the statistical errors, it does not necessarily follow that they
   formed at exactly the same time. At the estimated rate of impacts on
   the Earth, it would not be extremely unusual for a Boltysh-sized crater
   to be formed within half a million years of Chicxulub.

   However, the subsequent discovery of the Silverpit crater and its
   dating to approximately the same epoch gives greater weight to the
   theory that the Earth was struck by multiple impactors at this time.
   The dating of these impact craters is not yet accurate enough to
   establish whether the multiple impactors arrived over several thousand
   years, as part of a generally elevated rate of impacts at that time, or
   were almost simultaneous, like the impacts of the fragments of Comet
   Shoemaker-Levy 9 on Jupiter in 1994.

   Another crater to form at the same time was the Shiva crater.
   Retrieved from " http://en.wikipedia.org/wiki/Boltysh_crater"
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