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Tuesday, 21 March, 2000, 07:48 GMT
ET gases caged on Earth
Bucky Nasa
Impression of a buckyball and an encassed gas atom
Gases from space are caged inside carbon molecules and buried in clay sediments all around the world, scientists have found.

The researchers believe their discovery will yield a new way of tracing asteroid and comet impacts back through Earth's history.

The gases, which include helium, are constrained within so-called buckyballs or fullerenes, the hollow cages of carbon that look like soccer balls. These molecules, which come in various discrete sizes, have been the subject of intense study since their discovery in 1985.

News of buckyballs that contain gases known to have come from beyond Earth will strengthen the view that the carbon molecules are quite common in space.

The research also supports the theory that atmospheric gases and organic compounds arrived on the Earth's surface during asteroid and comet strikes early in our planet's history when such impacts were more common.

End of the dinosaurs

"We discovered extraterrestrial noble gases trapped inside buckyballs in a one-inch thick sedimentary layer of clay that is exposed at several locations on Earth," said Ted Bunch, a scientist at Nasa's Ames Research Center in California's Silicon Valley.

Bucky Nasa
Broken bonds in the cage could allow for the encapsulation of helium atoms
"The buckyballs containing the gases arrived on Earth about 65 million years ago during an asteroid impact that scientists theorise ended the age of the dinosaurs. The clay layer that formed from fallout of the impact debris was globally distributed."

Ted Bunch worked with Luann Becker, of the University of Hawaii, Honolulu, and Robert Poreda, of the University of Rochester, New York, on the research, which is published in the Proceedings of the National Academy of Sciences.

The scientists know the gases are of cosmic origin because they contain an unusual ratio of isotopes - different types of the same atom. Terrestrial helium, for example, consists of a small amount of helium-3 (the nucleus of which has two protons and one neutron), and mostly helium-4 (which has 2 protons and 2 neutrons). Cosmic helium is mostly helium-3.

Such helium was found inside fullerenes in well-studied, clay sediments that contain extraterrestrial iridium and highly shocked minerals resulting from an asteroid impact 65 million years ago. A highly shocked mineral is one that has experienced temperatures of more than 2,000degC and pressures of about 400,000 atmospheres from impact shock.

Atmospheric evolution

The clay layer, which is evident in Denmark, New Zealand and North America, documents a period of abrupt change in biological evolution, including mass extinction of the dinosaurs. This is now generally attributed to the impact of an asteroid with the Earth.

Kroto BBC
Buckyballs were discovered by Professor Harry Kroto and colleagues in 1985
Luann Becker hopes to expand the research to examine other deposits known to have been laid down during different periods of mass extinction.

"We now have a powerful new tracer to look at sediment layers very carefully," Becker said. "It opens new possibilities in looking at the problem of how planetary atmospheres evolved and maybe even how life evolved on Earth and perhaps on other moons and planets."

She said she also hopes to work with astronomers to study the formation of fullerenes. "We have yet to learn why these things are there and what they tell us about carbon in the Universe. We need to figure out how to establish their existence and how to search for it."

The latest research builds on a previous study which found fullerenes in the 4.6-billion-year-old Allende meteorite that landed in Mexico three decades ago.

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20 Jan 99 | Sci/Tech
Chemical cages
16 Jul 99 | Sci/Tech
Rare form of carbon found in space
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