Age dating crater counting

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Although it is not always possible to date a geologic event or surface on an absolute time scale, it may be possible to establish the order in which events occurred by the traditional methods of superposition and cross-cutting relationship among various geologic units.

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In practice, this procedure requires an accurate assessment of the initial abundances of the isotopes produced in the radioactive decay.The technique depends on an erosion model that relates the shape of a crater to the integrated flux of meteoroids and secondary debris that have impacted the surface since the crater was fresh.The method provides a means of estimating absolute surface ages in areas not sampled by the Apollo missions and suggests that some mare regions may be as young as about two billion years.Much work remains to be done, however, to refine the accuracy of these age estimates based on crater densities.More extensive telescopic observations are needed to improve our knowledge of the physical properties and collision rates of the planet-crossing bodies, and computer models must be refined to estimate [Another method that has been used successfully on the Moon to estimate absolute ages involves the correlation of the morphology of small craters (1 km in diameter) with the absolute age of a surface determined from isotopic measurements (Shoemaker, 1966).

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