Word: alvarezes
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Most scientists are waiting for that pudding to be served before they commit themselves to the idea of periodicity, let alone a particular model. Says Cornell Astronomer Carl Sagan: "None of the explanations is anything like fully satisfying." Yet all but a few diehards acknowledge the brilliance of the Alvarez work. They believe the iridium layer and subsequent discoveries indicate that impacts of extraterrestrial objects may have played a significant role in certain extinctions, either directly or by delivering a final coup de grace to species already debilitated by climatic changes...
Whether these catastrophic impacts are random or cyclic remains to be seen. But if they occur at all, they could shake the foundations of evolutionary biology and call into question the current concept of natural selection. Should the Alvarez theory be correct, says Harvard Paleontologist Stephen Jay Gould, the importance of competition between species diminishes. If every so often a megablast opens up a broad array of ecological niches, then new creatures can flourish without having to crowd out the old. "If you ask the question, 'Why are we here?' " says Gould, "the answer is, 'Because the dinosaurs disappeared...
...could it be that the permutations of life on earth are governed not by comets or death stars but by something more old-fashioned--like the fates? Although Shoemaker and Walter Alvarez do not consider themselves superstitious, they recently found reason to rethink their beliefs. During a visit to Berkeley, Shoemaker had roundly blasted the Nemesis idea, so Alvarez took him to a Chinese restaurant for a further discussion of Muller's model. After dinner, Alvarez cracked open his fortune cookie, pulled out the paper strip, glanced at it and, suppressing a laugh, handed it to Shoemaker. It read...
...revolution began with an unassuming element known as iridium, a rare and hard silvery-white metal related to platinum and gold. In the spring of 1977, Geologist Walter Alvarez of the University of California, Berkeley, was carefully chiseling through the rocks outside Gubbio, a medieval Italian town halfway between Florence and Rome, seeking clues to continental drift. Gubbio has long been an appealing site to geologists and paleontologists because its rocks provide a complete geological record of the critical boundary line between the end of the Cretaceous period, when the dinosaurs disappeared, and the Tertiary period, which followed...
...chiseled, Alvarez was struck by a configuration of sediment layers, which resembled a sandwich in stone. The bottom or older layer consisted of Cretaceous limestone, which was full of tiny fossils. On top was a second slice of limestone, from the Tertiary period, almost devoid of these fossils. Like other samples of rock from that era, it showed that the creatures alive during the late Cretaceous period had, by geological time scales, suddenly disappeared. In between the limestone layers was a dull red layer of clay about half an inch thick, first discovered by an Italian paleontologist around...