NEO News (02/22/01) Permian impact?

Dear Friends & Students of NEOs:

This edition of NEO News discusses new evidence from a team led by
geoscientist Luann Becker of the University of Washington indicating
that an impact was probably associated with the Permian-Triassic (PT)
mass extinction. This is the largest known mass extinction, in which
more than 90% of the families of macroscopic life went extinct. (As
an example, all the trilobites went extinct at this boundary.) Ever
since an impact cause for the KT mass extinction was identified more
than 20 years ago, scientists have speculated whether the PT mass
extinction might have a similar cause. The new evidence, based on
the discovery of the large carbon molecules called fullerenes in the
Permian-Triassic boundary layer, was presented today at a news
briefing at NASA Headquarters. The press release from these authors
notes that “recent studies suggest that the PT extinction occurred
very abruptly, consistent with a catastrophic, possibly
extraterrestrial, cause.” Their results are published in the
February 23 issue of Science.

Fullerenes have been used as an impact marker because of their high
geochemical stability and their association with other impact
structures. The extraterrestrial origin of these fullerenes is
determined by detailed isotopic analysis of the carbon as well as
trapped atoms such as helium; presumably these fullerenes actually
predate the formation of the solar system and were incorporated into
the impacting body (comet or asteroid) when it formed. Similar
fullerines have been found in the Allende and Murcheson carbonaceous

The Permian-Triasic mass extinction has been suggested previously to
be associated with the massive lava outpouring of the “Siberian
traps”. Becker and her colleagues suggested that perhaps an impact
provided a trigger for this volcanism, although this is purely
speculative. Previously an iridium anomaly had also been discovered
at the PT boundary, but it is about a factor of 10 smaller than the
iridium anomaly at the KT boundary. At the NASA news conference,
Chris Chyba (of the SETI Institute) suggested that the PT impactor
might have been cometary, as opposed to an asteroidal impactor at the

David Morrison

David Morrison, NASA Ames Research Center

Tel 650 604 5094; Fax 650 604 1165 or