- WASHINGTON (Reuters) - New evidence found deep within the Earth's crust
adds support to the theory that a huge asteroid smashed into the planet
65 million years ago and killed off the dinosaurs, researchers said on
Thursday.
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- They found extraterrestrial chromium
in the rocks that were on the surface of the Earth at about the time dinosaurs
disappeared.
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- Writing in the journal Science, the scientists
said they measured levels of a chromium isotope, 53Cr, in rocks at the
K-T boundary, the geologic layer in the Earth that coincides with dinosaur
extinction.
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- These rocks were at the surface when
the Cretaceous period ended and the Tertiary began, and when the dinosaurs
began their inexorable slide into extinction.
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- ``We found that this chromium is clearly
extraterrestrial,'' study author Alexander Shukolyukov, an associate project
scientist at the Scripps Institution of Oceanography at the University
of California San Diego, said in a telephone interview. ``It's clearly
different than that of the Earth.''
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- Isotopes are chemical variants of an
element, and the slight differences can show where they come from.
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- In this case, the researchers found extra
53Cr in the K-T rocks. The levels of 53Cr they found were different than
the 53Cr levels in all the other rocks and minerals on the planet, Shukolyukov
said.
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- Shukolyukov said 53Cr is formed when
a type of manganese, another element, breaks down radioactively. Lots of
53Cr can be found out in Space, but not too much is left on Earth.
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- Several studies have found evidence of
a huge asteroid impact around 65 million years ago, just when the dinosaurs
started to die off. There is a gigantic crater near Mexico's Yucatan peninsula
-- big enough to have blown dust and fragments high into the atmosphere,
from where they would have settled all over the Earth.
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- And there is evidence of extraterrestrial
dust everywhere from that time -- notably containing iridium, an element
rare on the Earth but found in extraterrestrial objects like asteroids.
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- The latest study adds to that evidence
the alien chromium.
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- Shukolyukov's team examined three samples
from rocks at the K-T boundary, one from Spain and two from Denmark. All
three showed 53Cr levels consistent with the makeup of some Space objects,
Shukolyukov said.
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- The scientists also tested some rocks
from just above and just below the boundary, finding 53Cr levels just like
those on the rest of Earth.
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- Shukolyukov's team said the high 53Cr
content of the asteroid, or whatever big object it was that hit the Earth
65 million years ago, was consistent with a carbonaceous chondrite, an
asteroid or meteorite that carries large amounts of carbon.
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- When this object crashed into Earth,
it was so big and hit so hard that it altered the planet's climate, making
it uninhabitable for the dinosaurs.
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- The discovery of yet more other-worldly
material in the rocks argues against a competing theory that underground
volcanic activity changed the climate and killed the dinosaurs, Shukolyukov
said.
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