John Bluck
NASA Ames Research Center, Moffett Field, CA
Phone: 650/604-5026, E-mail: jbluck@mail.arc.nasa.gov
Cheryl Ernst
University of Hawaii, Honolulu, HI
Phone: 808-956-5941, E-mail: ernst@hawaii.edu
RELEASE: 00-20AR
Extraterrestrial gases, including helium, are trapped in “buckyball”
molecules in a layer of sedimentary clay found in many places on Earth,
according to a paper to be published March 28, 2000, in the Proceedings of
the National Academy of Sciences.
The discovery provides a new tool for tracing asteroid and comet impacts in
Earth’s geological and biological records. A University of Hawaii
geochemist and her colleagues, including a NASA scientist, found gases that
did not originate on Earth inside buckyballs, or fullerene carbon
molecules.
The fullerene molecule is a hollow, cage-like structure typically made of
60 or more carbon atoms; it is also referred to as a “buckyball,” in honor
of Buckminster Fuller, designer of the geodesic dome that resembles the
molecule.
“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. “The buckyballs containing the gases
arrived on Earth about 65 million years ago during an asteroid impact that
scientists theorize ended the age of the dinosaurs. The clay layer that
formed from fallout of the impact debris was globally distributed,” Bunch
explained.
Luann Becker, of the University of Hawaii, Honolulu, HI; Robert Poreda, of
the University of Rochester, Rochester, NY; and Ted Bunch of NASA Ames,
discovered the extraterrestrial gases in the fullerenes. An advance copy
of the article will be posted on the Internet on March 21 at
http://www.pnas.org
“Helium from different sources on Earth, like our atmosphere or the
emissions from volcanoes, have a very different isotopic signature from the
helium in a meteorite,” Becker said. An isotopic signature is the ratio of
the isotopes of an element; for example, terrestrial helium consists of a
small amount of helium 3 (whose nucleus has two protons and one neutron),
and mostly helium 4 that has 2 protons and 2 neutrons. Cosmic helium is
mostly helium 3.
“The helium we found within the fullerene cages of Australia’s Murchison
meteorite, for example, is similar to the helium that existed when our
Solar System first formed,” Becker stated. That finding points to a cosmic
source for the fullerenes, the researchers say. In contrast, molecules
formed in the high pressure and temperature of an earthly impact or the
heat of wildfires that followed would have encapsulated terrestrial helium,
according to the researchers.
They say the finding also supports the theory that atmospheric
gases and organic compounds arrived on the Earth’s surface during asteroid
and comet strikes early in the planet’s history when impacts were very
numerous. The discovery relates to previous work by Becker and Bunch,
published in Nature in July 1999 that first identified naturally occurring
fullerenes in a meteorite. The scientists found significant quantities of
very large fullerene molecules, some containing as many as 400 carbon
atoms, in samples from the 4.6-billion-year-old Allende meteorite that
landed in Mexico three decades ago.
The subsequent work examined several Cretaceous/Tertiary boundary clay
sediments distributed worldwide, including deposits in Denmark, New Zealand
and North America. In each case, the researchers found fullerenes that
encapsulated noble gases with unmistakable extraterrestrial and possibly
extra-solar isotopic signatures.
The scientists examined the one-inch clay layer because it is a
well-studied sediment that contains 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 2,000 C and pressures of about 400,000 atmospheres from impact shock.
The clay layer documents a period of abrupt change in biological evolution,
including mass extinction of the dinosaurs, now generally attributed to the
impact of a carbonaceous asteroid with the Earth.
Becker said she hopes to expand the research to examine other periods of
mass extinction such as the even more devastating event that formed the
250-million-year-old Permian/Triassic layer of sediment. She added that she
hopes to determine if impacts with Earth trigger global change, including
whether fullerenes of extraterrestrial origin delivered gases and carbon
necessary to establish life on Earth.
“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.”
Grants from the NASA Cosmochemistry and Exobiology programs supported the
research.
