The F Irst H Urdle

How well, then, has the Alvarez theory done in meeting its first hurdle: being tested against the six predictions? It can be summed up as follows:

l . The K-T iridium anomaly is found worldwide.

2. With a few exceptions, the iridium enrichment is not found at other geological horizons.

3. Impact does produce distant ejecta deposits enriched in iridium.

•4. Almost everywhere the K-T boundary itself can be located around the earth, the boundary clay layer is present. Except for a few sites the layer is thin.

5. Accepted indicators of impact—quartz with planar deformation features, coesite and stishovite, and spherules that resemble microtektites—are present at many K-T locations.

6. The impact crater may have been found (see Chapter 7).

In addition, the seventh prediction, of unexpected discoveries, has not only been met, the surprising findings of soot, amino acids, meteoritic osmium isotopes, spinel, and finally diamonds, some of which are difficult or impossible to explain by terrestrial causes, help to corroborate the theory.

A neutral observer examining this evidence would have to conclude that the Alvarezes had a strong initial case for the impact half of their theory. But when a theory has potentially revolutionary consequences, few observers are neutral. Opponents of the theory immediately began to attack in earnest, arguing that either the tests were not valid, or, if they were, had failed. In this view, the iridium anomaly is not restricted to the K-T horizon; indeed, opponents claimed, iridium is not a true marker of impact at all. The boundary clay shows no sign of a meteoritic component; besides, shocked quartz and spherules are not diagnostic indicators of impact. The critics claimed repeatedly to have falsified the theory or to have found an alternative that fulfilled the predictions at least as well and that was consistent with uniformitarian doctrine to boot. The Alvarez team rebutted, the critics countered, and thereby was produced one of the most bitter scientific rivalries since the great controversy between dinosaur hunters Edward Drinker Cope and Othniel Marsh, who in the late nineteenth century quarreled openly for two decades about their interpretation of the dinosaur evidence, with one even accusing the other of stealing his fossils.

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