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The Body Electric
plankton animals with hard calcareous skeletons. Each species has a dis-
tinct, intricate shape, so their remains form an easily recognizable, con-
tinuous record in sediment cores. By 1967 James D. Hayes and Neil D.
Opdyke of Columbia's Lamont-Doherty Geological Observatory had cor-
related the disappearance of eight types of radiolarians with the reversals.
Each species had been widespread and abundant; each extinction took
place abruptly, with no previous decline in population. The "radiation
barrage" theory seemed confirmed.
However, it has since been learned that the field strength drops only
by half, not enough to drastically reduce the protective power of the Van
Allen belts and ionosphere. Moreover, radiolarian populations extend
down into several yards of water, which should protect them from the
radiation anyway. Hays has since drawn the less specific outlines of cur-
rent knowledge thus: As animals grow more specialized in the course of
evolution, they become more sensitive to some as yet unknown, lethal
effect of the reversals. Long periods without reversals—the quiescent
eras sometimes last tens of millions of years—seem to produce a profu-
sion of species especially susceptible to the effect, and they're weeded out
at the next shift.
We know of two especially widespread extinctions. One, at the end of
the Permian period, about 225 million years ago, wiped out half the
kinds of animals then alive, from protozoa to early reptiles. The same
kind of curtain dropped on the age of dinosaurs at the end of the Cre-
taceous period, some 70 million years ago. In both cases frequent mag-
netic pole reversals had resumed after a long quiescence. Many periods of
less extensive extinction have also been documented in the fossil record
and correlated with the field reversals. Most recently, J. John Sepkoski,
Jr., and David M. Raup of the University of Chicago reported what they
believed to be a 26-million-year cycle in the major dyings. If their hy-
pothesis holds up, there may be some solar or galactic influence that
interacts with a magnetic reversal for maximum destructive effect.
We can only surmise that the earth's field was instrumental in life's
beginning, but by 1971 we knew virtually for certain that its polarity
shifts had shaped life's development by a "pruning" of species. That year
I was invited to a private meeting at Lamont to talk about the reversals,
the sole M.D. among a score of biologists and geophysicists. At that
time we could only speculate as to how the extinction effect came about.
We didn't even have a workable theory of what changes inside the earth
caused the turnabouts, or how the process affected the micropulsations
and other aspects of the field.
All we could agree on was that there were
probably changes in every aspect of it, and our knowledge hasn't pro-
gressed much since then.