The last thing

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About ten, she told him. The last thing she had wished to do was to keep it secret, but no one had shown much interest. She gave him slides of the New York State east-west series, and told him that a comparable set could be got together for Pennsylvania, too. Harris went south and traversed the state of Tennessee, collecting carbonate rocks that were close in age, and when Anita ran the conodonts she found the color alterations quite the same as in the northern states-dark in the east, pale in the west. Leonard and Anita reported all this to Peter Rose, leader flexplek huren amersfoort of the Oil & Gas Branch, pointing out that the variations in conodont color could lead to a cheap and rapid technique of finding rock in the petroleum window. Rose said he couldn’t understand why no one in the United States had ever thought of this if it was as obvious as all that. Anita told him that for years she had been puzzled by the same question, since the procedure would be one that “any idiot ought to be able to follow, because all you need is to be not color-blind.” At Rose’s request, Anita’s division of the Geological Survey allowed her to work two days a week on conodonts. Weekends, she¬†worked on them at home. Actual temperature values had not been assigned to the varying colors. She did so in a year of experiments. She began with the palest of flexplek huren enschede conodonts from Kentucky and heated them at varying temperatures until they became canary and golden and amber and chocolate and cordovan, black, and gray. With enough added heat, they would turn white and then clear. At nine hundred degrees Celsius, they disintegrated. By cooking her samples in a great many variations of the ratio of time to temperature, she was able to develop a method of extrapolating laboratory findings onto the scale of geologic time. She concluded that pale-yellow conodonts could remain at about fifty degrees indefinitely without changing color. If they were to remain at sixty to ninety degrees for a million years or more, they would be amber. The earth’s thermal gradient varies locally, but generally speaking the temperature of rock increases about one degree Celsius for each hundred feet of depth. A conodont would have to be lodged in rock buried three thousand to six thousand feet in order to experience temperatures of the sort that would turn it amber.

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