# How potassium argon dating works

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.

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By using our site, you acknowledge that you have read and understand our Cookie Policy , Privacy Policy , and our Terms of Service. The Washington Post article Scientists discover hundreds of footprints left at the dawn of modern humanity describes the geological dating of stratified layers of mud by analyzing and dating minerals within each layer. But since floods jumble materials of different origins and ages together, that meant the scientists had to date dozens of different minerals.

The youngest crystal in the footprint layer would represent the oldest possible age for the prints; the oldest crystal in the layer above it would represent the youngest they could be. Using the argon-argon dating technique, by which scientists measure the decay of an isotope called Argon into Argon in order to find the age of crystals, they came up with a rough approximation of the footprints' age: I can't exactly follow the logic, but I'm asking here about the dating process itself.

How does argon-argon dating work? I do not think that Argon decays into Argon as the article states, at least not all by itself. And when I look at the Wikipedia article , the discussion is so technical and defensive that I can't actually picture what is going on. As noted in the comments the wikipedia articles at the time this question was submitted are contradictory. There are quite a few steps to the logic of how argon-argon dating works but none are too complicated, although I won't go into all of the possible interferences.

One thing to keep in mind is that high-precision isotope measurements always measure ratios between isotopes, not absolute concentrations. Potassium is radioactive but has such a long half-life that it is primordial - it has been around since the earth was being formed. Because of this, we can assume that the potassium Potassium decays in 2 different ways. Most decays by beta decay to calcium About If the argon stays trapped in the crystal and you can measure the ratio of potassium to argon, then you know how long it has been since the mineral formed.

This also assumes that there is no other source of argon like trapped air. A problem is that it takes two separate measurements to get the potassium concentration and the argon isotope ratios, increasing the uncertainty. Argon-argon dating gets around many of the issues by measuring only multiple isotopes of argon. The trick is to irradiate the sample with neutrons along with samples of known age.

Some of the potassium forms argon by an n,p reaction. By converting potassium to argon then measuring the argon The standards of known age are used to account for differences in the neutron flux during irradiation. Argon in the sample accounts for any air contamination. Home Questions Tags Users Unanswered. How does argon-argon dating work - need a simple but not-wrong explanation Ask Question.

But, I am not sure how the procedure works. The difference between measured Ar and Ar at formation is used in the procedure. But then, different passages in the Wikipedia article contradict each other first section: The Wiki article looks like there's well-intentioned effort, but it needs some attention from an expert. The Potassium 39 in the sample is irradiated to become Argon 39, then the ratio of the gas is compared.

The argon-argon method applies to a single sample but you need a 2nd sample of known age in this case. To understand argon-argon dating, you need to understand potassium-argon dating. Argon-argon dating, ideally assumes that: I edited it to say argon is formed by an n,p reaction. Is that about right? Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.

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## 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. Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on measurement of the.

Potassium—Argon dating or 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. Potassium is a common element found in many materials, such as micas , clay , tephra, and evaporites. In these materials, the decay product 40 Ar is able to escape the liquid molten rock, but starts to build up when the rock solidifies re crystallises.

Radiometric dating of rocks and minerals using naturally occurring, long-lived radioactive isotopes is troublesome for young-earth creationists because the techniques have provided overwhelming evidence of the antiquity of the earth and life. Some so-called creation scientists have attempted to show that radiometric dating does not work on theoretical grounds for example, Arndts and Overn ; Gill but such attempts invariably have fatal flaws see Dalrymple ; York and Dalrymple

Most people envision radiometric dating by analogy to sand grains in an hourglass: In principle, the potassium-argon K-Ar decay system is no different.

## Potassium-Argon Dating Methods

Some updates to this article are now available. The sections on the branching ratio and dating meteorites need updating. Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years. We are told that these methods are accurate to a few percent, and that there are many different methods.

## Radiometric Dating Does Work!

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. Carbon 14 dating 2. Potassium-argon K-Ar dating. K-Ar dating calculation. Atomic number, atomic mass, and isotopes. Current time:

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.

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.

## K–Ar dating facts for kids

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. However, the 40 K isotope is radioactive and therefore will be reduced in quantity over time. But, for the purposes of the KAr dating system, the relative abundance of 40 K is so small and its half-life is so long that its ratios with the other Potassium isotopes are considered constant. Argon, a noble gas, constitutes approximately 0. Because it is present within the atmosphere, every rock and mineral will have some quantity of Argon. Argon can mobilized into or out of a rock or mineral through alteration and thermal processes. Like Potassium, Argon cannot be significantly fractionated in nature. However, 40 Ar is the decay product of 40 K and therefore will increase in quantity over time.

## Potassium-argon dating

By using our site, you acknowledge that you have read and understand our Cookie Policy , Privacy Policy , and our Terms of Service. The Washington Post article Scientists discover hundreds of footprints left at the dawn of modern humanity describes the geological dating of stratified layers of mud by analyzing and dating minerals within each layer. But since floods jumble materials of different origins and ages together, that meant the scientists had to date dozens of different minerals. The youngest crystal in the footprint layer would represent the oldest possible age for the prints; the oldest crystal in the layer above it would represent the youngest they could be. Using the argon-argon dating technique, by which scientists measure the decay of an isotope called Argon into Argon in order to find the age of crystals, they came up with a rough approximation of the footprints' age: I can't exactly follow the logic, but I'm asking here about the dating process itself.

## K–Ar dating

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 The K-Ar method works by counting these radiogenic 40 Ar atoms trapped inside minerals.

## Potassium Argon Dating

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. Potassium is a common element found in many materials, such as micas , clay minerals , tephra , and evaporites. In these materials, the decay product 40 Ar is able to escape the liquid molten rock, but starts to accumulate when the rock solidifies recrystallizes. The amount of argon sublimation that occurs is a function of the purity of the sample, the composition of the mother material, and a number of other factors.

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. On the other hand, the abundance of argon in the Earth is relatively small because of its escape to the atmosphere during processes associated with volcanism.

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? Yet Potassium-Argon dates, for example, can easily go back to the time that evolutionists believe the earth began; 4,,, years ago 4. That is six orders of magnitude larger than what the Bible says Creation Week occurred!

K-Ar dating calculation - Life on earth and in the universe - Cosmology & Astronomy - Khan Academy