# Line graphs and radiometric dating technique

### How reliable is geologic dating?

Radioactive parent elements decay to stable daughter elements. Radioactivity was (see graph, above) Glauconite contains potassium, so it can be dated using the potassium-argon technique. Return to Georgia Geoscience On-line. Radiometric dating. Used to determine absolute age of the. Earth based on radiometric dating Examine the graph that plots the . the 4 colored lines represent 4 different isotopes. Another useful method of radiometric dating involves. Principles of Radiometric Dating . Note also that equation (5) has the form of a linear equation, i.e. . Pb - i.e. Pb separated from continents and thus from average crust also plots on the Geochron, Other Dating Methods.

These half-lives have been measured over the last years. They are not calibrated by fossils. No one has measured the decay rates directly; we only know them from inference.

Decay rates have been directly measured over the last years. In some cases a batch of the pure parent material is weighed and then set aside for a long time and then the resulting daughter material is weighed.

In many cases it is easier to detect radioactive decays by the energy burst that each decay gives off. For this a batch of the pure parent material is carefully weighed and then put in front of a Geiger counter or gamma-ray detector. These instruments count the number of decays over a long time. If the half-lives are billions of years, it is impossible to determine them from measuring over just a few years or decades. The example given in the section [in Wiens' article] titled, "The Radiometric Clocks" shows that an accurate determination of the half-life is easily achieved by direct counting of decays over a decade or shorter.

Additionally, lavas of historically known ages have been correctly dated even using methods with long half-lives. The decay rates are poorly known, so the dates are inaccurate. Most of the decay rates used for dating rocks are known to within two percent. Such small uncertainties are no reason to dismiss radiometric dating.

**Half Life Chemistry Problems - Nuclear Radioactive Decay Calculations Practice Examples**

Whether a rock is million years or million years old does not make a great deal of difference. To date a rock one must know the original amount of the parent element. But there is no way to measure how much parent element was originally there. It is very easy to calculate the original parent abundance, but that information is not needed to date the rock.

All of the dating schemes work from knowing the present abundances of the parent and daughter isotopes. There is little or no way to tell how much of the decay product, that is, the daughter isotope, was originally in the rock, leading to anomalously old ages.

A good part of [Wiens' article] is devoted to explaining how one can tell how much of a given element or isotope was originally present. Usually it involves using more than one sample from a given rock. It is done by comparing the ratios of parent and daughter isotopes relative to a stable isotope for samples with different relative amounts of the parent isotope.

From this one can determine how much of the daughter isotope would be present if there had been no parent isotope.

This is the same as the initial amount it would not change if there were no parent isotope to decay. Figures 4 and 5 [in Wiens' article], and the accompanying explanation, tell how this is done most of the time.

There are only a few different dating methods. There are actually many more methods out there. Well over forty different radiometric dating methods are in use, and a number of non-radiogenic methods not even mentioned here.

A young-Earth research group reported that they sent a rock erupted in from Mount Saint Helens volcano to a dating lab and got back a potassium-argon age of several million years. This shows we should not trust radiometric dating. There are indeed ways to "trick" radiometric dating if a single dating method is improperly used on a sample. Anyone can move the hands on a clock and get the wrong time.

Likewise, people actively looking for incorrect radiometric dates can in fact get them. Geologists have known for over forty years that the potassium-argon method cannot be used on rocks only twenty to thirty years old. Publicizing this incorrect age as a completely new finding was inappropriate.

The reasons are discussed in the Potassium-Argon Dating section [of Wiens' article]. Be assured that multiple dating methods used together on igneous rocks are almost always correct unless the sample is too difficult to date due to factors such as metamorphism or a large fraction of xenoliths. Different dating techniques usually give conflicting results. This is not true at all. The fact that dating techniques most often agree with each other is why scientists tend to trust them in the first place.

Nearly every college and university library in the country has periodicals such as Science, Nature, and specific geology journals that give the results of dating studies. The public is usually welcome to and should! So the results are not hidden; people can go look at the results for themselves. Over a thousand research papers are published a year on radiometric dating, essentially all in agreement.

Besides the scientific periodicals that carry up-to-date research reports, [there are] textbooks, non-classroom books, and web resources. Anomalies As noted above, creationists make great hay out of "anomalies" in radiometric dating.

It is true that some "anomalies" have been observed, although keep in mind that these have been identified by professional scientists in published literature, not by creationists or others outside of peer-reviewed scientific literature.

First of all, many of these claimed "anomalies" are completely irrelevant to the central issue of whether the Earth is many millions of years old. This is certainly true when errors are in the range of a few percent in specimens many millions of years old. This is also true of anomalies noted in carbon dates. Carbon dating cannot be used to date anything older than about 50, years, since the carbon half life is only years. For additional discussion, see Radiocarbon dating.

In any event, it is important to keep these anomalies in perspective. For example, out of literally tens of thousands of dates measured using the rubidium-strontium dating scheme see description of the Rb-Sr scheme in Agesonly about 30 cases have been noted where the individual data values initially appeared to lie nearly on a straight line as is requiredbut the result was later found to be significantly in error.

And each of these 30 cases is fairly well understood -- none of these is truly "mysterious" [ Wien ]. Anomalies and other objections that have been raised by creationists are dealt with in detail in Roger Wiens' article [ Wien ], Mark Isaak's book [ Isaakpg.

A detailed response to other claims of scientific evidence for a young Earth is given by Matthew Tiscareno [ Tiscareno ].

### Decay graphs and half lives article (article) | Khan Academy

Radioactive isotopes and the age of the Earth Until recently, only a large scientific laboratories could afford mass spectrometers, which are the principal tool used to measure dates of rock samples. But recently the prices of these devices have dropped to levels that even amateur meteorite hunters and others can afford. Used mass spectrometers are currently available at eBay.

Some have said that the last of the flat-earth believers did not give up until they could hold GPS receivers in their hand that give their latitude-longitude position. Will skeptics of old-earth geology wait until mass spectrometers are in every home before finally conceding that the Earth is older than years?

In any event, there is a simple way to see that the Earth must be at least 1. The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life in other words raised to a power equal to the number of half-lives.

To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed.

## Graphing Half Life WS

Contrary to creationist claims, it is possible to make that determination, as the following will explain: By way of background, all atoms of a given element have the same number of protons in the nucleus; however, the number of neutrons in the nucleus can vary. An atom with the same number of protons in the nucleus but a different number of neutrons is called an isotope.

For example, uranium is an isotope of uranium, because it has 3 more neutrons in the nucleus. 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. The element potassium symbol K has three nuclides, K39, K40, and K Only K40 is radioactive; the other two are stable.

K40 can decay in two different ways: 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 gas, it 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.

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. 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. 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. See Carbon 14 Dating in this web site. 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.

## Radiometric Dating

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. 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. Therefore the relative amounts of rubidium and strontium can be determined by expressing their ratios to strontium These curves are illustrated in Fig It turns out to be a straight line with a slope of The corresponding half lives for each plotted point are marked on the line and identified.

It can be readily seen from the plots that when this procedure is followed with different amounts of Rb87 in different minerals, if the plotted half life points are connected, a straight line going through the origin is produced. These lines are called "isochrons". The steeper the slope of the isochron, the more half lives it represents. When the fraction of rubidium is plotted against the fraction of strontium for a number of different minerals from the same magma an isochron is obtained.

If the points lie on a straight line, this indicates that the data is consistent and probably accurate.