Radioactive isotopes in dating the past


21-Sep-2015 20:55

To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques.These include some that establish a relative chronology in which occurrences can be placed in the correct sequence relative to one another or to some known succession of events.See also fission-track dating; helium dating; lead-210 dating; rubidium-strontium dating; uranium-234–uranium-238 dating; uranium-thorium-lead dating.in geology, determining a chronology or calendar of events in the history of the Earth, using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments.Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information.The record of changes in polarity of the Earth's magnetic field has provided a timescale for seafloor spreading and long-term marine sedimentation.Dendrochronology has proved useful in archaeology and climatology.For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.

Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy) or a presumed evolution in form or structure, or absolute dating, in which items are assigned a date independent of context.The latter type includes potassium-argon and carbon-14 dating; both are based on the measurement of radioactive decay.



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