History of the time scale and names British geologists were also responsible for the grouping of periods into Eras and the subdivision of the Tertiary and Quaternary periods into epochs. When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, time scales could be estimated only very imprecisely since various kinds of rates of change used in estimation were highly variable. While creationists had been proposing dates of around six or seven thousand years for the age of the Earth based on the Bible , early geologists were suggesting millions of years for geologic periods with some even suggesting a virtually infinite age for the Earth. Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering , erosion , sedimentation , and lithification . Until the discovery of radioactivity in 1896 and the
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