Travel Reference
In-Depth Information
the information necessary for decoding the polarity of the earth's magnetic
field at the time the rock was formed. Yet obtaining an oriented core is only
the first part of the process of arriving at ancient magnetic directions. Once
collected, the core must be analyzed in a large and complex machine called
a magnetometer. The intensity of the earth's magnetic field itself is small,
and the amount of magnetic signal given off by the magnetite grains found
within a core 2 inches long and 1 inch in diameter is minute. The magne-
tometer was devised to measure these very tiny magnetic fields still existing
within the cores.
Like so much in science, the theory is deceptively simple: An oriented
core is extracted from some unsuspecting rock and taken back to a labora-
tory. There it is put into a gargantuan electrified machine out of Baron von
Frankenstein's worst nightmare, and
voila,
a number flashed on some com-
puter screen tells you whether the rocks from which the core was taken were
deposited when the earth's polarity was normal or reversed. And, as in a low-
budget ad on TV, you get the something else thrown in absolutely free—in
this case, a measurement of the field intensity from the rocks you have sam-
pled and the inclination and declination of the magnetic field from the age
and locality you have sampled. These latter bonuses can provide some of the
most interesting information of all; they can tell you the ancient latitude of
the rocks you have sampled. I was seduced. At the time, no one had sampled
Cretaceous-aged rocks for western North America, and the whole procedure
seemed so sttaightfotward: Drill some cores, analyze them, and end up with
a polarity history that could he matched to the Italian wotk completed by
Lowrie and Alvarez. Why not? What could go wrong? What could be easier
than deciding in a binary system? All one needed to find out was whether the
fossil magnetic signal in the rocks reported a normal or a reversed polarity for
any given time.
Who has not been so seduced, be it for a used car, a VCR, or a new part-
ner with no baggage? I took the bait, swallowed it, and headed off into the
California hills with all the equipment needed to drill hundreds of small
cores from the rocks. And everything worked—the first few times. (That's
the secret of a really effective con: Make it work—at first.)
