Geoscience Reference
In-Depth Information
a distinguished, if somewhat iconoclastic, paleontologist; Sepkoski's
career was barely underway. Neither wanted to become a laughing-
stock, or perhaps worse, to be ignored. They stuck their toes in recep-
tive water when Sepkoski presented their preliminary findings at a
1983 symposium in Flagstaff, Arizona, home of the Astrogeology
Branch of the U.S. Geological Survey (founded by Shoemaker). This
friendly audience, assembled to explore the implications of the
Alvarez theory, was delighted, and Sepkoski was emboldened to sug-
gest that the source of the periodicity might be extraterrestrial. As
Raup tells it, this proposal arose merely because it is much easier to
find cycles in the motions of the planets, stars, and galaxies, which
wheel and circle each other periodically, than to find them in appar-
ently random earthly processes. The astronomers and astrophysicists
in attendance at the meeting, intrigued by the Raup and Sepkoski
analysis, set to work with a vengeance to find the cause of the
26-million-year cycle.
With no reason to delay publishing, Raup and Sepkoski chose the
Proceedings of the National Academy of Sciences (PNAS),
the journal
of that elite group of elected, eminent scientists, of which Luis
Alvarez and Raup were members. The
PNAS
publishes only papers
written by members, which it does not find necessary to subject to
peer review. Their paper appeared in February 1984.
7
The reaction came almost too quickly to be true. In the April
19, 1984, issue of
Nature
no fewer than five articles appeared based
on the
PNAS
paper.
8
Now, although
Nature
is one of the speedier
journals to publish, the submission dates on the five papers showed
that they were submitted even
before
the Raup and Sepkoski paper
appeared] The explanation is that Raup and Sepkoski, like most sci-
entists, sent preprints of their submitted paper to colleagues, giving
them advance warning.
One of the five papers, by Michael Rampino and Richard
Stothers, confirmed the periodicity of the fossil record. Using a dif-
ferent statistical technique, they reanalyzed the Raup-Sepkoski data
set and came up with a period of 30 ± 1 million years, which they
attributed to the passage of our solar system through the plane of
the Galaxy. As everyone knows, our solar system is part of the Milky
Way, a vast, rotating complex of stars shaped like a planar disk—
broad and spiraling when viewed from "above" but flat when seen
edge on. As the Galaxy rotates, the Sun and planets move slowly up
and down across the plane of the disk, the round trip taking just
over 60 million years. The solar system thus crosses the galactic
plane twice in each such circuit—once every 30 million years or so,
not too far off the period that Raup and Sepkoski, and Rampino and
