Radiometric dating
is used to estimate the age of the rock surrounding a fossil, not the fossil itself.
Radiometric dating is the determination of the age of materials (typically rocks) by analyzing the decay of radioactive isotopes in the material. The best-known form of radiometric dating is radiocarbon dating, which uses carbon-14 as the dating isotope. Radiometric dating has been in widespread use for more than half a century.
Function
Rocks are composed of individual crystals, and each crystal is made up of at least several different chemical elements such as silicon, iron, magnesium, etc. Most elements in nature are "stable," meaning that they decay radioactively over extremely long periods of time. Other elements, however, undergo radioactive decay at a much quicker rate, causing their atoms to change from one element to another.
Radioactive Decay
If there are a lot of atoms of the original element, the atoms will decay and change to another element at a predictable rate. The passage of time can be charted by the reduction in the number of original atoms and the increase in the number of changed atoms. Scientists refer to the original atoms as "parent" atoms and the changed atoms as "daughter" atoms. The decay rate of an element (hereafter referred to as a radioactive isotope) is listed in terms of its half-life---the length of time it takes for half of the parent atoms to decay into daughter atoms.
Radiometric Hourglass
Think of radiometric dating as an hourglass. In our radiometric hourglass example, the individual grains of sand are radioactive atoms. The sand runs from top to bottom, representing radioactive decay. You cannot say when one particular grain will fall to the bottom, but you can predict how long it will take for all the sand to fall. Using mathematical techniques based on probability and the known rates of decay of an element, scientists can estimate how much time has passed since some event occurred.
Different Techniques
Just as there are different types of hourglasses and clocks which are more or less suitable for measuring different lengths of time, there are different radiometric dating techniques. According to The American Scientific Affiliation, "there are over 40 different radiometric dating techniques, each based on a different radioactive isotope." Different isotopes decay at different rates. Isotopes with very short half-lives are not useful for dating very ancient events, just as isotopes with very long half-lives are not suitable for measuring more recent events.
Archaeologists prefer to use the carbon-14 dating technique, which has a half-life of 5,730 years and is useful for dating recent organic remains. This technique is not suitable for measuring time scales older than about 70,000 years, however, so other isotopes with half-lives of millions of years are used to date prehistoric rock formations.
Peer Review
The principal criticism of radiometric dating techniques is that the resulting data is only an estimate, especially by people who assert the universe was created 6,000 years ago (according to the Christian Bible). It is true that this technique is based on probabilities and a few assumptions about the percentage of daughter atoms present in a sample. However, since radiometric dating began, results have been cross-tested by scientists all over the planet and reinforced by related dating methods such as sequencing (the order in which rock layers form and the type of fossils found in each layer).
Tags: dating techniques, daughter atoms, radiometric dating, radiometric dating techniques, suitable measuring
