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Source: University of California-Los Angeles (via UASR)
Date: 18 November 1998
Written by: Stuart Wolpert, stuartw@college.ucla.edu
UCLA Geochemist's Fossil Meteorite Provides Strong Evidence that Asteroid Caused Mass Extinctions 65 Million Years Ago
UCLA geochemist Frank T. Kyte has found a fossil meteorite believed to be from the huge asteroid that crashed to Earth 65 million years ago -- the probable cause of the extinction of the dinosaurs and many other species worldwide.
In the cover story of the Nov. 19 issue of the journal Nature, Kyte presents his analysis of the sample and concludes that the cosmic impactor, some six miles in diameter, that broadsided Mexico's Yucatan peninsula was probably an asteroid, and not a comet.
"The fossil meteorite strongly supports the idea that the impactor was an asteroid and not a comet," Kyte said. "There is a strong probability that this is a bullet from a smoking gun."
"That was one of the worst days the Earth had in the last billion years, and it is important to understand what happened."
Kyte's analysis of the sample's texture and chemistry confirmed that the object is a meteorite. He considers it highly likely that the sample is from the asteroid that struck 65 million years ago, and if so, it is the first piece of the asteroid that is large enough to study and analyze.
What is Kyte's evidence that the meteorite was from an asteroid? First, comets travel at much higher velocities than asteroids, most likely vaporizing themselves on collision, Kyte noted. Therefore, the mere fact that a sample survived the impact is evidence that the object was not a comet, he said.
Second, Kyte's analysis suggests that the meteorite came from a typical, rocky carbonaceous chondrite -- a description of objects in the asteroid belt -- rather than the porous, fluffy type of interplanetary dust associated with icy comets.
The fossil meteorite was encrusted in mud for 65 million years, buried beneath more than 50 yards of sediment in the North Pacific Ocean. It no longer has any of its original minerals, but its texture and shape remain the same, Kyte said.
Kyte located the piece while studying a sediment layer from the Cretaceous/Tertiary boundary -- whose sediments are widely recognized to contain the record of a large asteroid or comet impact -- and suspected right away that he found an important clue to the mystery of what happened 65 million years ago.
"Although the fossil meteorite is only a tenth of an inch in size, it was 1,000 times bigger than anything else in the sediment, "Kyte said. "In this dark brown sediment, I saw this small white speck."
In his National Science Foundation-funded research, Kyte analyzed the piece using UCLA's electron microprobe and neutron activation laboratories. He found it to be high in iridium -- an element that is abundant in meteorites.
"That's when I knew I had something special -- a small chunk of the asteroid," Kyte said.
Asteroids, which originate in the asteroid belt between Mars and Jupiter, are pieces of largely rocky material remaining from early in the evolution of the solar system. They did not form into planets, probably because of their close proximity to Jupiter. A typical asteroid travels at about 40,000 miles per hour, Kyte noted. Comets are from beyond Pluto, and travel about twice as fast, he said. Comets are believed to be composed of about half rocky material and half icy material.
Some scientists think the destructive meteorite 65 million years ago is an example of comet showers that bombard the Earth every 25-30 million years, causing mass extinctions. If the impact was from an asteroid, as Kyte believes, such theories become harder to defend, he said.
The impact 65 million years ago, at the end of what is known as the Cretaceous period, is believed to have had devastating effects on the world's climate, and has been implicated in the extinction of the dinosaurs and many other forms of life. Prior to the crash, a few thousand dinosaur species had thrived for 160 million years.
Questions remain about how the asteroid affected the environment, how long it took for the extinctions to occur, and the exact size of the massive object.
Source: Reuters
Date: 29 October 1998
Written by: Mark Weinraub
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.
They found extraterrestrial chromium in the rocks that were on the surface of the Earth at about the time dinosaurs disappeared.
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.
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.
``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.''
Isotopes are chemical variants of an element, and the slight differences can show where they come from.
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.
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.
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.
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.
The latest study adds to that evidence the alien chromium.
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.
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.
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.
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.
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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