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First Direct Evidence Of Fullerenes In Meteorite Samples

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25.06.2003

The first direct evidence of fullerenes in material originating from outer space could reinforce the meteorite impact theory of mass extinction on Earth and the existence of fullerenes in interstellar dust. The existence, or not, of the closed-cage carbon molecules known as fullerenes in outer space has been an area of controversy. A team from Reading University in the UK is publishing its findings in Proceedings A, a Royal Society scientific journal.

Allende meteorite

The measurements were made by high power transmission electron microscopy on samples from the Allende meteorite. This meteorite fell on Mexico in 1969 and previous work has shown that it was formed at the time of planet formation in our solar system. The meteorite contains large amounts of carbon and some of this material was extracted for analysis.

"Our images show numerous completely closed fullerene particles," say Dr. Peter Harris of Reading University. "These giant fullerene particles would contain around 6,000 to 10,000 carbon atoms and are seen in a generally disordered carbon structure of curved and faceted graphite-like sheets of carbon. We also see voids enclosed in the graphitic sheets that are 2 - 10 nanometres in size."

The observations show directly that fullerenes are present in the carbonaceous materials of the Allende meteorite and could therefore be capable of surviving for billions of years in space. "Certain spectroscopic signals from interstellar dust - for example the ultraviolet absorption at 217 nanometres - could be consistent with the presence of large amounts of fullerenes in the dust," explains Dr. Harris. "Our results reinforce that possibility."



The observation has relevance to theories about the mass extinction events that occurred on Earth between the Cretaceous and Tertiary and the Permian and Triassic periods, respectively 65 million and 251 million years ago.

"A group of scientists led by Luann Becker at the University of Washington in Seattle has previously claimed that fullerenes are present in carbonaceous material from meteorites," explains Dr. Harris. "This group has also claimed to find fullerenes in boundary layers between the Cretaceous and Tertiary and Permian and Triassic periods and have proposed a link. Moreover Becker has proposed that fullerenes could be the medium that carry primordial extraterrestrial noble gases in meteorites." These gases have a distinctive, and different, isotopic "signature" compared to terrestrial gases and Becker has also claimed to find these gases at the extinction boundary layers.

However Becker’s work is controversial as the method of detection - laser desorption mass spectroscopy (LDMS) - could have formed fullerene compounds. "The power of the laser used to vapourise samples for analysis by mass spectroscopy could have modified the carbon samples producing fullerenes," says Dr. Harris. "This has made many people question the results - our results show directly that fullerenes are present and therefore add credence to the theory of meteorite impact as the reason for extinction in both events."

Fullerenes

The fullerenes are a class of carbon molecules with cage-like structures, of which the best known is the football-shaped molecule buckminsterfullerene, C60, or the "buckyball". Since their discovery in the mid-eighties fullerenes have been the subject of much research as a "third phase" of carbon for new materials science and nanotechnology.

Tim Reynolds | Source: alphagalileo
Further information: www.royalsoc.ac.uk

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