Geologic Time - History Of The Concept Of Geologic Time, Relative Age Determination, Radiometric Age Determination
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Although historical time covers centuries, and archeological times covers millennia, geologic time describes the immense span of time—billions of years—revealed in the fossil and rock record of Earth. Geochronology is the science of finding out how old rocks and minerals are. Absolute time and relative time are terms used to describe the age of rocks and events used by geologists. Radiometric age determination is a method used by geologists to determine the absolute age, in years, of rocks and minerals. Knowledge of stratigraphy, the branch of geology that catalogues Earth's successions of rock layers, is essential to establish the relative ages of rock units. By finding which rock unit formed first, the order of the events in Earth history can be sorted out.
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Before scientific methods were used to investigate geologic time, ideas about time and Earth history came from religious theories. The Hindu and Mayan religions taught about endlessly repeating cycles of time, each lasting for billions of years. Ideas in western culture about the age of Earth were just as imprecise, and just as incorrect. In the 1650s, the Irish clergyman and scholar James Ussher …
Every rock and mineral exists in the world as a mixture of elements, and every element exists as a population of atoms. One element's population of atoms will not all have the same number of neutrons, and so two or more kinds of the same element will have different atomic masses or atomic numbers. These different kinds of the same chemical element are called nuclides of that element. A nucl…
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