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No. 71: Sep-Oct 1990

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Pennsylvanian time-scale problems

The advent of radiometric dating seemed to solve once and for all the problem of assigning dates to the key events in the earth's history. Indeed, all of the reference books confidently label charts with firm dates for the appearance of fishes, the demise of the dinosaurs, and so on. Alas, things are not quite as certain as they appear. Radiometric dating is not all that precise; errors may be large indeed.

Take the Pennsylvanian period for example. It is part of the Carboniferous period, when many of the great coal deposits were laid down. The classical duration of the Pennsylvanian -- used in many texts -- is 34 million years. A meticulous new study of central European stratigraphy now pegs the Pennsylvanian as spanning only 19 million years. Now that's a 44% change!

This new figure for the duration of the Pennsylvanian has already cast doubt on the origin of the famous Pennsylvanian cyclothems (repetitive strata) in North America. It had been thought that these seemingly cyclic deposits were correlated with sea level changes forced by variations in the earth's orbit (the Milankovitch periods). With this substantial compression of Pennsylvan-ian time, this correlation falls apart. The cyclothems, which are of impressive area and thickness, now seem to have been created by some other, still unrecognized phenomenon. (Klein, George deV.; "Pennsylvanian Time Scales and Cycle Periods," Geology, 18:455, 1990.)

Comment. Even worse, perhaps, is the fuzziness conferred on the entire geological time scale by this compression of the Pennsylvanian and the possibility of similar revisions for other periods.

From Science Frontiers #71, SEP-OCT 1990. 1990-2000 William R. Corliss

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  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

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