# What is potassium argon dating

Potassium-argon dating , method of determining the time of origin of rocks by measuring the ratio of radioactive argon to radioactive potassium in the rock. This dating method is based upon the decay of radioactive potassium to radioactive argon in minerals and rocks; potassium also decays to calcium Thus, the ratio of argon and potassium and radiogenic calcium to potassium in a mineral or rock is a measure of the age of the sample. The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.

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It seems that you're in Germany. We have a dedicated site for Germany. Perhaps no dating method has the wide range of applicability as does the potassium argon dating method from either consideration of the ranges of ages which can be dated or the availability of suitable material to date. Minerals as young as tens of thousands of years to minerals billions of years old have been successfully dated.

Many minerals retain for times of the order of billions of years the daughter, Ar40, and many minerals contain as a component K40 the parent element, potassium being a common element in the earth's crust. As a result, most rock contains at least one mineral which can be successfully dated by the potassium argon method. Even though this method has been applied for over fifteen years, there is as yet no work which summarizes the experimental techniques and the results available.

The sixtieth birthday ofW. JavaScript is currently disabled, this site works much better if you enable JavaScript in your browser. Free Preview. Buy eBook. Buy Softcover. FAQ Policy. About this book Perhaps no dating method has the wide range of applicability as does the potassium argon dating method from either consideration of the ranges of ages which can be dated or the availability of suitable material to date. Show all. Pages Determination of Radiogenic Argon Kirsten, T.

Tektites Schaeffer, O. Show next xx. Read this book on SpringerLink. Recommended for you. PAGE 1.

## Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the. Chronological Methods 9 - Potassium-Argon Dating. Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating.

An absolute dating technique similar to radiocarbon dating but applicable to much older deposits. It is used to determine the age of volcanic rock strata containing or sealing archaeological objects rather than to date the artefacts themselves. In volcanic rocks any argon present will have escaped when the rock was last molten but will start to accumulate again when it solidifies. Thus by carefully measuring the amount of 40 K and 40 Ar present in a sample it is possible to work out how long ago it was that the rock solidified.

Potassium—argon dating , abbreviated K—Ar dating , is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium K into argon Ar.

Donald L. Turner,

## potassium-argon dating

Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals. The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present. Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral. Potassium can be mobilized into or out of a rock or mineral through alteration processes. Due to the relatively heavy atomic weight of potassium, insignificant fractionation of the different potassium isotopes occurs.

## K–Ar dating

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. A Nature Research Journal. THE potential of the potassium—argon technique in the dating of young rocks can be evaluated by applying it to intrusive igneous rocks which are well dated by conventional geological methods. Because of their possible interest, we are reporting the dating of two such igneous rocks. Rhyolite plugs of Plio-Pleistocene age intrude and upturn sedimentary formations of late Cretaceous to early Pliocene age. Erosion uncovered the rhyolite plugs before the ensuing period of andesitic intrusions and extrusions, suggesting that the entire igneous cycle covered many thousands of years. Canyons 1, ft.

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However, it is well established that volcanic rocks e. If so, then the K-Ar and Ar-Ar "dating" of crustal rocks would be similarly questionable.

## Radiometric Dating and Paleontologic Zonation

Potassium-argon dating is a method for estimating the age of volcanic rocks by measuring the ratio of potassium to argon present. The method is based on the fact that the potassium isotope of potassium decays over time to form argon The useful fact about these two substances is that at normal temperatures, potassium is a solid, but argon is a gas. Therefore, during volcanic eruptions, any argon that is present escapes from the rock. But after the rock solidifies, any potassium that is present continues to decay, and the argon that is produced cannot escape from the rock. Thus, geologists use potassium-argon dating to measure the age of volcanic rocks. If the concentration of argon is almost zero, then the rock was formed recently. If it is high relative to the amount of potassium present, then the rock is old. Archaeologists and biologists are also sometimes able to use potassium-argon dating to measure the age of artifacts and fossils, when these have become trapped in or buried under volcanic rock. The mathematical formula that is used to figure the age of the rock depends on the half-life of potassium the time it takes for half the potassium in a given sample to decay. The half-live of potassium is approximately 1. Obviously, this formula depends on the laws of physics remaining constant over time.

## potassium-argon dating

Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating very old archaeological materials. Geologists have used this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, Potassium K ,decays to the gas Argon as Argon Ar By comparing the proportion of K to Ar in a sample of volcanic rock, and knowing the decay rate of K, the date that the rock formed can be determined. How Does the Reaction Work? Potassium K is one of the most abundant elements in the Earth's crust 2. One out of every 10, Potassium atoms is radioactive Potassium K

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The potassium-argon K-Ar isotopic dating method is especially useful for determining the age of lavas. Developed in the s, it was important in developing the theory of plate tectonics and in calibrating the geologic time scale. Potassium occurs in two stable isotopes 41 K and 39 K and one radioactive isotope 40 K. Potassium decays with a half-life of million years, meaning that half of the 40 K atoms are gone after that span of time. Its decay yields argon and calcium in a ratio of 11 to

## Potassium-Argon and Argon-Argon Dating of Crustal Rocks and the Problem of Excess Argon

The attraction of the method lies in the fact that one of the daughter elements is argon which is an inert gas. This means that the geologist can plausibly assume that all argon gas escapes from the molten magma while it is still liquid. He thinks this solves his problem of not knowing the initial quantity of the daughter element in the past and not being able to go back in time and make measurements. He assumes the initial argon content is zero. He assumes that any argon that he measures in his rock sample must have been produced by the radioactive decay of potassium since the time the rock solidified. He imagines that his radioactive hour glass sealed when the rock solidified, and his radioactive clock started running. And he hopes the rock has remained sealed until the time he collected his sample. With these assumptions the geologist only needs to measure the relative amounts of potassium and argon in the rock at the present time to be able to calculate an age for the rock.

## potassium–argon dating

If you are having problems understanding concepts such as Average Nuclear binding Energy and nuclide stability; What is it that drives fission; fusion; and other nuclear reactions; Types of radioactive decay, alpha, beta, gamma, positron, and a summary of characteristics; Nuclear reactions; Nuclear equations; The use of nuclide charts to visually chart out nuclear reactions; The U decay series shown on a nuclide chart. See the Nuclear Reactions Page. If you are having problems understanding the basics of radioisotopes techniques, such as. See the introduction to Radiometric dating techniques Page. Is the prevalent view held by the majority of scientists the only plausible way of approaching the problems of time?

If you're seeing this message, it means we're having trouble loading external resources on our website. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. Science Biology History of life on Earth Radiometric dating. Chronometric revolution. Carbon 14 dating 1.

Rant 19 - Potassium Argon Dating Proves Old Earth