Geoscience Reference
In-Depth Information
FIGURE
2 7 A grand unified theory of earth systems? [After Stothers and
Rampino.
23
]
Rampino and Stothers are onto something. Yet recall that the K-T
boundary is not the only one to have a flood basalt of nearly, if not
exactly, the same age: so does the Permian-Triassic. Its age matches
closely, some say identically, that of the Siberian traps. Rampino,
Stothers, and most recently, French geologist Vincent Courtillot, have
searched the literature for other examples of geologic boundaries
with flood basalts of similar age, and have found many.
2
4
On the
other hand, just as some craters appear to have no associated ex-
tinction, neither do some flood basalt eruptions. The boundary
that we know best, the K-T, formed 1 million or 2 million years
after the Deccan flood basalt volcanism began. The age of the Per-
mian-Triassic boundary is not as well dated as the K-T, and it remains
to be seen whether the claimed correspondence between the age of
the Permian-Triassic and that of the Siberian traps will hold up.
P
ERIODICITY
A
SSESSED
Writing in 1989 and basing his remarks on his latest compilation of
the extinction rate for genera, Sepkoski concluded that 9 of 11
extinction peaks lie on or close to the 26-million-year periodicity.
The probability of this happening by chance is less than one in a
