Mysterious Spherules

While working on the iridium-rich K-T boundary clay at Caravaca, Spain, in 1981, Jan Smit and G. Klaver discovered rounded, sand-sized grains of feldspar.42 Similar spherules showed up at the other prominent K-T sites and in several deep-sea cores that captured the boundary. On the basis of the mineralogy and texture of the spherules, Smit, Alessandro Montanari, the Alvarezes, and their colleagues concluded that they were congealed droplets of molten material that had been blasted aloft in the K-T impact explosion.43 Wezel and his group reported that, like iridium, the spherules spread out above and below the K-T boundary at Gubbio, undercutting the claim for a special event at the boundary.44 Officer and two colleagues from Dartmouth wrote that they had found spherules over a vertical span of rock at Gubbio equivalent to 22 million years, analogous to their alleged findings of spread-out iridium.45 The Wezel claim led to one of the more bizarre episodes in the debates over the Alvarez theory, which is saying a lot. Officer presented Wezel's results at the 1985 meeting of the American Geophysical Union, but Montanari, who had also collected and studied the Gub-bio spherules, came up with quite a different interpretation of what Wezel and company had found, which he then shared with his colleague, Walter Alvarez. Let us pick up the story in the words of the protagonists, as reported by Malcolm Browne in the New York Times of January 19, 1988:

But according to Dr. Alvarez, "My son Walt took just two minutes to demolish Officer after he delivered that paper." Dr. Alvarez said his son showed that the "spherules" found by Dr. Officer's team were merely insect eggs and had been mistaken for mineral spherules because they were not cleaned well enough. "At that point," Dr. Alvarez wrote in his autobiography, "the audience of several hundred Earth scientists burst into laughter, something I'd never witnessed before in my 53 years of attending scientific meetings."

Dr. Officer responded: "This is a misstatement. There was no outburst of laughter following Walter's brief comment, and no direct or implied derision of me as a scientist by the audience." "My talk at that meeting," he said, "concerned the hypothesis that intense volcanic activity and the lowering of sea levels explains the mass extinctions at the end of the Cretaceous. During that talk, mention was made of the distribution of microspherules. Walter had kindly pointed out to us previously that there were contaminant hollow spherules of recent origin as well as solid spherules of a mineral composition indigenous to the geologic section."

"After duly eliminating the insect eggs and giving due credit to Walter in our subsequent scientific publications," Dr. Officer said, "we found that all the solid spherules, throughout the whole section, extended above and below the terminal Cretaceous layer. They were present in sediments spanning a time period of several million years and could therefore not have come from impact."46

As research continued, the spherules turned up at over 60 K-T sites. Those found outside the United States were solid, rich in nickel and iron, and often composed of spinel. Some of the spinels have iridium concentrations of up to 500 ppt. These spinels are not a dispersed chemical element like iridium, which for all we know can be dissolved and reprecipitated, and whose exact source in the boundary clay is not known to this day, but rather are physical objects—spherules up to 100 microns (1 micron = 10~6 m) in diameter. Once locked into a sediment, these spherules would be difficult to move and thus they help to decide whether the strange features of the boundary clay—iridium, shocked quartz, spherules—were originally present in a peak or in a hill. A group of French geologists found that at El Kef, Morocco, and at several other K-T sites, iridium spreads over a broad hill, but the spinels occur in a razor-sharp peak right at the boundary.47 They concluded that the spinels (and thus the boundary clay) took less than 100 years to deposit—a blink of the eye in geologic time.

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  • negassi
    What is spherules dinosaur?
    9 years ago

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