Isotopes used for radiometric dating

Most rocks contain uranium, allowing uranium-lead and similar methods to date them.Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy.

Isotopes used for radiometric dating

Through analysis, a bone fragment is determined to contain 13% of its original carbon-14.

The half-life of carbon-14 is approximately 5,730 years. Since the quantity represents 13% (or 13/100ths) of , it follows that This is based on the decay of rubidium isotopes to strontium isotopes, and can be used to date rocks or to relate organisms to the rocks on which they formed.

Another limitation is that carbon-14 can only tell you when something was last alive, not when it was used.

A limitation with all forms of radiometric dating is that they depend on the presence of certain elements in the substance to be dated.

Due to the long half-life of uranium it is not suitable for short time periods, such as most archaeological purposes, but it can date the oldest rocks on earth.

A proper radiometric date should read years before present (with 1950 being present) ± range/2 at x standard deviations (Xσ)', but is often reported as a single year or a year range, like 1260–1390 CE (the date for the Shroud of Turin).

Radiometric dating — through processes similar to those outlined in the example problem above — frequently reveals that rocks, fossils, etc.

are very much older than the approximately 6,000 to 10,000 years reckoned by young earth creationists.

This leaves out important information which would tell you how precise is the dating result.

Carbon-14 dating has an interesting limitation in that the ratio of regular carbon to carbon-14 in the air is not constant and therefore any date must be calibrated using dendrochronology.

One problem is that potassium is also highly mobile and may move into older rocks.

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