Abslute dating

Although relative ages can generally be established on a local scale, the events recorded in rocks from different locations can be integrated into a picture of regional or global scale only if their sequence in time is firmly established.

The time that has elapsed since certain minerals formed can now be determined because of the presence of a small amount of natural radioactive atoms in their...

Each isotope is identified with what is called a ‘mass number’.Although development of radiometric methods led to the first breakthroughs in establishing an absolute time scale, other absolute methods have limited applications.Chief among these are dendochronology, varve analysis, hydration dating, and TL dating.Dendochronology This method of dating is based on the number, width, and density of annual growth rings of long-lived trees.A master tree-ring index has been constructed in the southwestern United States for the Douglas fir and bristlecone pine.There is no particular reason to suspect that this will turn out to be the case when it comes to the laws underlying absolute dating; nonetheless, an argument from principle alone can never be entirely convincing. You will recall from our discussion of sea floor spreading that the sea floor spreads out from mid-ocean rifts, and so ought to be younger nearer the rifts and progressively older further away from them.

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