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Many radioactive dating methods are based on minute additions of daughter products to a rock or mineral in which a considerable amount of daughter-type isotopes already exists. These isotopes did not come from radioactive decay in the system but rather formed during the original creation of the elements. In this case, it is a big advantage to present the data in a form in which the abundance of both the parent and daughter isotopes are given with respect to the abundance of the initial background daughter. The incremental additions of the daughter type can then be viewed in proportion to the abundance of parent atoms. In mathematical terms this is achieved as follows.

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It has the same number of protons, otherwise it wouldn't be uranium. The number of protons in the nucleus of an atom is called its atomic number. The sum of protons plus neutrons is the mass number.

We designate a specific group of atoms by using the term "nuclide. Only K40 is radioactive; the other two are stable. K40 can decay in two different ways: it can break down into either calcium or argon.

# Dating strontium

The ratio of calcium formed to argon formed is fixed and known. Therefore the amount of argon formed provides a direct measurement of the amount of potassium present in the specimen when it was originally formed. Because argon is an inert gasit is not possible that it might have been in the mineral when it was first formed from molten magma. Any argon present in a mineral containing potassium must have been formed as the result of radioactive decay.

F, the fraction of K40 remaining, is equal to the amount of potassium in the sample, divided by the sum of potassium in the sample plus the calculated amount of potassium required to produce the amount of argon found.

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The age can then be calculated from equation 1. In spite of the fact that it is a gas, the argon is trapped in the mineral and can't escape.

Creationists claim that argon escape renders age determinations invalid. However, any escaping argon gas would lead to a determined age younger, not older, than actual. The creationist "argon escape" theory does not support their young earth model.

Overview Information Strontium is a silvery metal found naturally as a non-radioactive element. About 99of the strontium in the human body is concentrated in the bones. Dating - Dating - Rubidium-strontium method: The radioactive decay of rubidium (87Rb) to strontium (87Sr) was the first widely used dating system that utilized the isochron method. Rubidium is a relatively abundant trace element in Earth's crust and can be found in many common rock-forming minerals in which it substitutes for the major element potassium. Although rubidium-strontium dating is not as precise as the uranium-lead method, it was the first to be exploited and has provided much of the prevailing knowledge of Earth history. The procedures of sample preparation, chemical separation, and mass spectrometry are relatively easy to carry out, and datable minerals occur in most rocks.

The argon age determination of the mineral can be confirmed by measuring the loss of potassium. In old rocks, there will be less potassium present than was required to form the mineral, because some of it has been transmuted to argon.

### Potassium-argon (K-Ar) dating - Cosmology \u0026 Astronomy - Khan Academy

The decrease in the amount of potassium required to form the original mineral has consistently confirmed the age as determined by the amount of argon formed. Carbon dating: See Carbon 14 Dating in this web site. Rubidium-Strontium dating: The nuclide rubidium decays, with a half life of Strontium is a stable element; it does not undergo further radioactive decay. Do not confuse with the highly radioactive isotope, strontium Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.

Note that this does not mean that the ratios are the same everywhere on earth. It merely means that the ratios are the same in the particular magma from which the test sample was later taken.

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As strontium forms, its ratio to strontium will increase. Strontium is a stable element that does not undergo radioactive change. In addition, it is not formed as the result of a radioactive decay process.

The amount of strontium in a given mineral sample will not change. During fractional crystallizationSr tends to become concentrated in plagioclaseleaving Rb in the liquid phase. Highest ratios 10 or higher occur in pegmatites. For example, consider the case of an igneous rock such as a granite that contains several major Sr-bearing minerals including plagioclase feldsparK-feldsparhornblendebiotiteand muscovite.

Rubidium substitutes for potassium within the lattice of minerals at a rate proportional to its concentration within the melt. The ideal scenario according to Bowen's reaction series would see a granite melt begin crystallizing a cumulate assemblage of plagioclase and hornblende i.

This then causes orthoclase and biotite, both K rich minerals into which Rb can substitute, to precipitate. The resulting Rb-Sr ratios and Rb and Sr abundances of both the whole rocks and their component minerals will be markedly different.

This, thus, allows a different rate of radiogenic Sr to evolve in the separate rocks and their component minerals as time progresses.

The Rubidium-Strontium Dating Method multicoingames.com Page 3 87Rb/86Sr, Ages Dating Summary Average 28, Maximum 91, Minimum 3, Difference 88, Table 5 There is almost a 90 billion years difference between the oldest and youngest dates. Below we can see some of the maximum ages and how stupid they are. 87Rb/86Sr, Maximum Ages Age Age. Rubidium-Strontium dating: The nuclide rubidium decays, with a half life of billion years, to strontium Strontium is a stable element; it does not undergo further radioactive decay. (Do not confuse with the highly radioactive isotope, strontium) Strontium occurs naturally as a mixture of several nuclides, including the stable. Rubidium-strontium (Rb-Sr) dating was the first technique in which the whole-rock isochron method was extensively employed. Certain rocks that cooled quickly at the surface were found to give precisely defined linear isochrons, but many others did not.

The age of a sample is determined by analysing several minerals within multiple subsamples from different parts of the original sample. If these form a straight line then the subsamples are consistent, and the age probably reliable. The slope of the line dictates the age of the sample.

After measurements of Rubidum and Strontium concentration in the mineral we can easily determine the age, the t value, of the sample. Several preconditions must be satisfied before a Rb-Sr date can be considered as representing the time of emplacement or formation of a rock. With modern analytical methods, however, uncertainties in measured ages have been reduced to 20 million years for the oldest rocks and meteorites. Mineral isochrons provide the best results. The equation relating present-day neodymium isotopic abundance as the sum of the initial ratios and radiogenic additions is that of a straight line, as discussed earlier for rubidium-strontium.

Other successful examples have been reported where rocks with open rubidium-strontium systems have been shown to have closed samarium-neodymium systems.

In other examples, the ages of rocks with insufficient rubidium for dating have been successfully determined. There is considerable promise for dating garneta common metamorphic mineral, because it is known to concentrate the parent isotope. In general, the use of the samarium-neodymium method as a dating tool is limited by the fact that other methods mainly the uranium-lead approach are more precise and require fewer analyses.

In the case of meteorites and lunar rocks where samples are limited and minerals for other dating methods are not available, the samarium-neodymium method can provide the best ages possible. Article Media.

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Strontium 90 dating Delores Mcdonald February 04, Radioactive substances have 60 strontium from soils are considered. Objective to carbon in the period. Assessment for example, collected in seawater. Dilcardia sr with a tentative reference method for douglas labs strontium 90 90sr, by determining the harmful effects in nuclear multicoingames.com: Delores Mcdonald. 'Rubidium-strontium dating relies on the decay of rubidium to strontium' 'Techniques such as potassium-argon dating and rubidium-strontium dating are fundamental to our ability to put a date on fossils, relating them to the span of geological time.'. Rubidium-strontium dating, method of estimating the age of rocks, minerals, and meteorites from measurements of the amount of the stable isotope strontium formed by the decay of the unstable isotope rubidium that was present in the rock at the time of its formation. Rubidium comprises percent of the total atomic abundance of rubidium, and of the four isotopes of strontium, only.

Dating metamorphic rocks Should a simple igneous body be subjected to an episode of heating or of deformation or of a combination of both, a well-documented special data pattern develops.

Samarium-neodymium method The radioactive decay of samarium of mass Sm to neodymium of mass Nd has been shown to be capable of providing useful isochron ages for certain geologic materials.