Earth history at the century mark of the U.S. Geological Survey.
Earth history involves all aspects of geological and biological evolution, especially paleontology and stratigraphy. Early paleontological exploration of the western United States by and before the U.S. Geological Survey featured the dramatic discoveries and rivalries of the great vertebrate paleontologists Leidy, Cope, Marsh, and Osborn. Invertebrate paleontology and paleobotany in the U.S. Geological Survey blossomed with emphasis on practical missions. The most illuminating and useful earth history, nevertheless, emerges where there is a high degree of interaction with academic scholars. Despite a good knowledge of its broad features, the drama of earth history remains obscure in detail. Whereas it speaks conclusively for the reality of organic evolution, it is less conclusive about mechanisms and many important transitions. Current investigations, however, especially in pre-Phanerozoic, mammalian, and human paleontology, promise improved insights. New techniques in collecting, sample preparation, and research are revealing previously unknown kinds of fossils and exquisite details of preservation. Plate tectonic theory provides a new framework for historical geography and biogeography. Emerging techniques in geochronology-matching paleopolarity sequences, for example-promise to resolve old problems of the synchroneity or heterochroneity of different biotal provinces. As it splits into subfields, the teaching and practice of paleontology expand to cover all of them. The fossils themselves, however, remain the basic objective evidence. All hypotheses about them must answer to this court of appeal. But nature rarely responds in an either-or way. The most probable hypotheses are those that have repeatedly confronted objective reality and survived all opportunity for disproof.
Simpson
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Professor of Geosciences, University of Arizona, Tucson, Arizona 85721, and President, Simroe Foundation.