Earth's most severe mass extinction - an event 250 million years ago that wiped out 90 percent of all marine species and 70 percent of land vertebrates - was triggered by a collision with a comet or asteroid, according to a team led by The University of Washington, Seattle, USA. Evidence is based upon elegant findings involving carbon molecules called buckminsterfullerenes (C₆₀, Buckyballs) with the gases helium and argon trapped inside their cage structures.

The scientists do not know the site of the impact 250 million years ago, when all Earth's land formed a supercontinent called Pangea. However, the space body left a calling card - a much higher level of complex carbon molecules called buckminsterfullerenes, or Buckyballs, with the noble (or chemically nonreactive) gases helium and argon trapped inside their cage structures. Fullerenes, which contain 60 or more carbon atoms and have a structure resembling a soccer ball or a geodesic dome, are named for Buckminster Fuller, who invented the geodesic dome.

The researchers know these particular Buckyballs are extraterrestrial because the noble gases trapped inside have an unusual ratio of isotopes. For instance, terrestrial helium is mostly helium-4 and contains only a small amount of helium-3, while extraterrestrial helium - the kind found in these fullerenes - is mostly helium-3.

"These things form in carbon stars. That's what's exciting about finding fullerenes as a tracer," according to Luann Becker, one of scientific team involved. The extreme temperatures and gas pressures in carbon stars are perhaps the only way extraterrestrial noble gases could be forced inside a fullerene, she said. These gas-laden fullerenes were formed outside the Solar System, and their concentration at the Permian-Triassic boundary means they were delivered by a comet or asteroid.

A physicsweb.org article states that an international team working at the ISOLTRAP mass spectrometer at CERN has determined the masses of two isotopes of argon (³²Ar and ³³Ar) with the highest precision ever. This is important if you want "to place constraints on aspects of the weak interaction that are not included in the Standard Model".1

• 1. Masses of Ar-32 and Ar-33 for Fundamental Tests,
  Blaum, K., Audi G., Beck D., Bollen G., Herfurth F., Kellerbauer A., Kluge H. - J., Sauvan E., and Schwarz S.
  , Phys. Rev. Lett., 12/2003, Volume 91, Number 26, p.260801, (2003)
  

Masses of the short-lived radionuclides ³²Ar (T_1/2=98   ms) and ³³Ar (T_1/2=173   ms) have been determined with the Penning trap mass spectrometer ISOLTRAP. Relative uncertainties of 6.0×10-8 (δm=1.8   keV) and 1.4×10-8 (δm=0.44   keV), respectively, have been achieved. At present, these new mass data serve as the most stringent test of the quadratic form of the isobaric-multiplet mass equation. Furthermore, the improved accuracy for the mass of ³²Ar will allow for a better constraint on scalar contributions to the weak interaction. New mass values have also been measured for ⁴⁴Ar and ⁴⁵Ar, and a 20σ deviation for ⁴⁴Ar from the literature value was found and interpreted.

Masses of Ar-32 and Ar-33 for Fundamental Tests, Blaum, K., Audi G., Beck D., Bollen G., Herfurth F., Kellerbauer A., Kluge H. - J., Sauvan E., and Schwarz S. , Phys. Rev. Lett., 12/2003, Volume 91, Number 26, p.260801, (2003)