Travel Reference
In-Depth Information
privacy. We rationalized our illegal trespass on the principle that science was
more important than land rights, but in truth the hunters probably didn't
care. They rarely visited their land this time of year and in any case were far
less likely to resent our activities than those of the local pot farmers who
managed the land farther upstream. All around me I could see the results of
our labors: On the edge of the creek were piles of white bags, each contain-
ing a tubular rock core about 2 inches long and an inch in diameter. In the
bank I could see the scars that yielded up these cores, small holes bored into
the solid rock by our gasoline-powered drills modified from chain saws. Also
on the creekside lay: cloth sample bags filled with pearly fossils: beautiful
coiled ammonites and flat whitened clams wrested by hammer blow from the
entombing sediment that makes up the creek bottom and its canyons. It had
been 12 hours since we had climbed out of sleeping bags. I suppose I was
tired, but how tired could you be at 30 years old, when you believe you are
on the verge of putting an accurate age on sediments known to scientists for
over a century? How tired can you be sitting naked in a cool creek with noth-
ing left to do that day except scrounge up dinner? We had taken samples that
would tie us into a web of research that originated with the classic work done
in France and Italy—the tegions first studied by the pioneering geologists a
century or more before us.
The geomagnetic polarity time scale
The two most common methods for distinguishing units of geological time
are using fossils (which yields only a relative age) and measuring the ra-
dioactive decay of one isotope into another, which yields an age in years. Yet
if you reside in a land where the fossils are unique and new, or where none of
the rocks contain the elusive minerals that embody radiometric clocks, you
have no way to tell your rocks' age. Luckily for those interested in the age of
rocks from the west coast of North America, however, there are other meth-
ods as well. One of the most powerful yet least expected timekeepers em-
anates from the earth's magnetic field. In California, in the early 1980s, I was
the first to use paleomagnetism (as this dating system is called) to arrive at
