Geoscience Reference
In-Depth Information
of TNT. Traveling at 25 km/sec or more, the mountain-sized mete-
orite would strike the earth with the force of 100
million megatons
of TNT (10
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4
tons; 10 followed by 14 zeros), more than 7 billion
times as much energy as the bomb dropped on Hiroshima—in fact,
vastly more energy than the explosion of
all
of the 60,000 nuclear
weapons that existed at the height of the Cold War. To comprehend
the power of meteorite impact, try to imagine the simultaneous
explosion of 7 billion bombs like the one dropped on Hiroshima—
one for every person on earth and 10 for every square kilometer of
the earth's surface. The terrorist bomb that destroyed the Alfred P.
Murrah Federal Building in Oklahoma City in 1995 had an energy
equivalent measured not in megatons, not in kilotons, but in tons—
2.5
tons.
The K-T impact was 40 trillion times larger. The dinosaurs,
concluded the Alvarezes, never had a chance.
LOSING
BY A
NOSE
Even today, in the era of electronic mail, faxes, and international
flight, it is still possible for two individuals or groups to work inde-
pendently, unknown to each other, and to come to the same con-
clusion simultaneously. This nearly happened in the case of the
meteorite impact theory.
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In 1974, geologist Jan Smit began to
study the K-T boundary at Caravaca, Spain, for his doctoral disser-
tation, focusing on the disappearance of the microscopic foramin-
ifera there. At the start, he thought their sudden exit at the bound-
ary was only apparent, caused by an erosional gap that made a
gradual extinction appear falsely sharp. But the sudden extinction
persisted even in sections without visible gaps. Smit decided to see
whether there were invisible, chemical changes.
In the spring of 1977, he sent off to the Dutch interuniversity
laboratory in Delft a set of 100 K-T samples for neutron activation
analysis, asking the scientists there to determine the concentrations
of various elements. Because there was no reason for him to do so,
Smit did not include iridium on his list of elements to be studied.
When the results came back, the thin boundary clay turned out to
have concentrations of nickel, cobalt, chromium, arsenic, antimony,
and selenium that were orders of magnitude higher than in the
limestones on either side. Smit published his finding that the
extinctions were rapid, and, as he describes it, "began to speculate
about extraterrestrial causes."
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4
What Smit did not know was that
the iridium levels of his samples had actually been available in the
analysis records, but, since they had not been requested, were not
