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Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: Principles of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the nucleus of an atom will escape through the potential (Energy) barrier which bonds them to the nucleus.
The Rb-Sr ratios in various rock samples from the same lava flow might differ, but all should plot as a straight line on the graph if the lava was isotopically homogeneous (each rock sample had the same initial Sr ratio) and each rock remained closed to gain or loss of rubidium and strontium since crystallization.
In the ideal case, multiple samples from the same lava flow should plot perfectly along a line with slope e Ar give lines whose slopes supposedly reflect the ages of lava flows.
those that form during chemical reactions without breaking down).
The unstable or more commonly known radioactive isotopes break down by radioactive decay into other isotopes.
Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials.
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.
The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.
Popular Dating Methods Both the K-Ar and Rb-Sr methods make use of radioactive decay of a parent isotope to a stable daughter isotope. Leeman, "Late Cenozoic Alkali-Rich Basalt from the Western Grand Canyon Area, Utah and Arizona: Isotopic Composition of Strontium," Geological Society of America Bulletin, 85 (Nov. Six analyses of Uinkaret Plateau basalts (U-33, U-35, U-59, U-24, U-43, U-58) were used.