"Jeff Hecht - Extinction Theory" - читать интересную книгу автора (Hecht Jeff)

for really rare elements -- things like osmium and iridium that are down at a
part per billion or less. All it takes to make the readings can go way off is
a finger that's been wearing a wedding ring. We learned that the hard way,
after one of the grad students got married, and everything she touched came
out wrong. Wasserman is scrupulous in the field, or so he says. I've never had
any trouble with contaminants, but we never had to look for anything that
might rub off aluminum beer cans.
The purpose of it all was understanding mass extinctions, like the one
that got the dinosaurs and lots of other things at the end of the Cretaceous
65 million years ago. Ever since the Alvarezes found the iridium anomaly in
that boundary clay, every geologist in creation has been asking physicists how
to count isotopes and measure concentrations of rare metals. I get requests
for strontium and neodymium isotope ratios, and wish lists that get
ridiculous. Everything has its own meaning. The geologists say that strontium
isotopes should tell if there was acid rain after an asteroid impact;
neodymium ratios vary from ocean to ocean and change with time.
When it started, I just ran the stuff through the laser, collected the
data, and got my name at the bottom of the list of authors. It wasn't a bad
way to build up publications. Wasserman gave papers at the big geophysics
meetings, and he got into the thick of some of the debates. He argued for the
impact theories, but never could convince himself anything was periodic. He
told me that he'd seen a statistical analysis that found periodicity in random
numbers. Behind his back, I told my grad students that it was his personal
experience with the drunkard's walk.
I got into it more when we started running samples from the end of the
Triassic, and some of the other major extinction points. Wasserman was
selective about his samples; he just wanted certain intervals. Most of the
time he went after known extinctions and iridium anomalies. He kept asking for
data on more rare elements and isotopes.
"What are you trying to find?" I asked him when he called in from Spain
early one morning.
"Patterns," he replied in his most enigmatic voice. The transatlantic
phone line was erratic that day, and I couldn't understand most what he said,
but "Patterns" echoed back and forth between my ears for the rest of the day.
When he came back from that field trip, he spent two full days staring
at my data logs. He had asked me to take isotope ratios for one-millimeter
slices of several cores, from well above the boundary clay to well below. All
sorts of things varied. The changes were small, but they were real. He
scratched his head and walked in circles around the table where he had spread
out the readings.
The third day, he came back in the morning sharp and sober as I had
ever seen him. He wanted to brainstorm, and his favorite foil in the geology
department was on a field trip.
It might have gotten nowhere if Karelski over in chemistry hadn't
gotten a fat contract from the EPA to study pollution deposition in coastal
waters. She had taken cores that went back hundreds of years in places like
Boston Harbor, then asked me to analyze the glop. The variations were
striking. The harbor sediments weren't layered as neatly as Wasserman's rocks,
of course, but the trends were equally dramatic. Things like mercury and lead
residues rose dramatically with the advance of what we call civilization, then