Scientists supporting the idea that impact events from meteors or asteroids caused many of Earth’s mass extinctions may now have a new tool to help search for clues. Fullerenes, sphere-shaped carbon molecules that look like soccer balls, are often formed in space. Fullerenes with 60 or more atoms can trap noble gases such as helium. On Earth, these carbon soccer balls protect helium and other noble gases from the atmosphere, according to a recent report.

“Fullerenes with trapped helium could be a very robust tracer of extraterrestrial flux,” says Luann Becker of the University of Hawaii and lead author of the report published in the March 28 Proceedings of the National Academy of Sciences. When other tracers are not obvious, such as iridium or shocked quartz, fullerenes and helium may also help indicate whether mass extinctions at boundary events could be related to impacts, she says. Becker, Robert J. Poreda of the University of Rochester and Ted E. Bunch of NASA Ames Research Center discovered fullerenes containing noble gases in the Allende and Murchison meteorites as well as in the Cretaceous/Tertiary boundary layer. The fullerenes trapped helium well above the ratios  accepted for solar wind or reported for Earth’s mantle.

Luann Becker holds a buckyball. University of Hawaii

“This is going to be an important area of research for a long time,” says Paul R. Renne, director of the University of California at Berkeley Geochronology Center. “It is a complex problem with many questions about how the fullerenes form, and under what pressure and temperature. Did they come in on the meteors or rather were they formed on impact?”

Initially, Becker, Poreda and Jeffrey L. Bada of Scripps Institution of Oceanography became interested in investigating the K/T boundary as well as two carbonaceous chrondrite meteorites after studying carbon-60 and carbon-70 fullerenes found in the Sudbury Impact Structure in Ontario, Canada, in 1996. The fullerenes contained trapped helium with ratios similar to those in interplanetary dust particles.

Fullerenes were originally discovered in 1985. In 1996, three chemists won the Nobel Prize for identifying the most symmetrical of the fullerenes: buckminsterfullerene. Also known as buckyballs, the fullerenes’ 60 carbon atoms are linked together in 12 pentagons and 20 hexagons and look similar in structure to the geodesic dome designed by R. Buckminster Fuller.

In 1994, other researchers had detected carbon-60 and other large fullerenes at the K/T boundary. However, those researchers were not investigating fullerenes’ ability to trap noble gases and said the carbon molecules appeared in the boundary because of massive wildfires triggered by the impact event.

“Our interpretation is the first to report helium trapped in fullerene isolated from the boundary layer,” Becker says. “We did look above and below the K/T boundary and we did not find fullerene or helium. In this way fullerene and helium seem to be coupled with iridium.”

Evidence of high iridium levels, shocked quartz, microtektites, spherules, spinel from contact metamorphism, and diamonds all helped identify the impact at the K/T boundary. But so far, it is the only impact linked to a mass extinction.

Fullerenes may help provide a tracer of extraterrestrial material at times of climatic and biostratigraphic change, Becker says. She is currently working on identifying helium ratios in fullerenes found at the Permian/Triassic boundary. “We hope to be able to determine how much material was coming to Earth and will further evaluate how these events coincide with what we see in the geologic record.”

Christina Reed