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This means that lifeless organic matter is effectively a closed system, since no carbon enters the organism after death, an occurrence that would affect accurate measurements. In radiometric dating, the decaying matter is called the parent isotope and the stable outcome of the decay is called the daughter product. Since the half-life of carbon is years, scientists can measure the age of a sample by determining how many times its original carbon amount has been cut in half since the death of the organism. In all radiometric procedures there is a specific age range for when a technique can be used.

If there is too much daughter product in this case nitrogen , age is hard to determine since the half-life does not make up a significant percentage of the material's age. The range of practical use for carbon dating is roughly a few hundred years to fifty thousand years. The isotope potassium k decays into a fixed ratio of calcium and argon Since argon is a noble gas, it would have escaped the rock-formation process, and therefore any argon in a rock sample should have been formed as a result of k decay.

The half-life of this process is 1. In rubidium-strontium dating a rubidium isotope becomes the daughter product strontium In an igneous rock formation, the entirety of the cooled rock will have the same ratio of strontium and strontium another stable isotope. This means that as the rubidium decays and more strontium is formed, the ratio will change.

The half-life of rubidium is Uranium-lead dating is one of the most complicated of all dating techniques. One key assumption is that the initial quantity of the parent element can be determined. With uranium-lead dating, for example, the process assumes the original proportion of uranium in the sample. One assumption that can be made is that all the lead in the sample was once uranium, but if there was lead there to start with, this assumption is not valid, and any date based on that assumption will be incorrect too old.

In the case of carbon dating, it is not the initial quantity that is important, but the initial ratio of C 14 to C 12 , but the same principle otherwise applies.

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Recognizing this problem, scientists try to focus on rocks that do not contain the decay product originally. For example, in uranium-lead dating, they use rocks containing zircon ZrSiO 4 , though it can be used on other materials, such as baddeleyite. Zircon has a very high closure temperature, is very chemically inert, and is resistant to mechanical weathering.

For these reasons, if a rock strata contains zircon, running a uranium-lead test on a zircon sample will produce a radiometric dating result that is less dependent on the initial quantity problem. Another assumption is that the rate of decay is constant over long periods of time, which is particularly implausible as energy levels changed enormously over time.

There is no reason to expect that the rate of decay of a radioactive material is largely constant, [3] and it was almost certainly not constant near the creation or beginning of the universe. As early as of , John Ray, an English naturalist, reckoned with alternative that "im the primitive times and soon after the Creation the earth suffered far more concussions and mutations in its superficial part than afterward".

## What are some of the limits of radiometric dating techniques?

Atoms consist of a heavy central core called the nucleus surrounded by clouds of lightweight particles electrons , called electron shells. The energy locked in the nucleus is enormous, but cannot be released easily. The phenomenon we know as heat is simply the jiggling around of atoms and their components, so in principle a high enough temperature could cause the components of the core to break out. However, the temperature required to do this is in in the millions of degrees, so this cannot be achieved by any natural process that we know about.

The second way that a nucleus could be disrupted is by particles striking it. However, the nucleus has a strong positive charge and the electron shells have a strong negative charge. Any incoming negative charge would be deflected by the electron shell and any positive charge that penetrated the electron shells would be deflected by the positive charge of the nucleus itself. Particles consist of various subtypes.

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Those that can decay are mesons and baryons , which include protons and neutrons ; although decays can involve other particles such as photons , electrons , positrons , and neutrinos. This can happen due to one of three forces or "interactions": Historically, these are also known as alpha, gamma, and beta decays, respectively. For example, a neutron-deficient nucleus may decay weakly by converting a proton in a neutron to conserve its positive electric charge, it ejects a positron, as well as a neutrino to conserve the quantum lepton number ; thus the hypothetical atom loses a proton and increments down the table by one element.

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A complex set of rules describes the details of particle decays: Decays are very random, but for different elements are observed to conform to statistically averaged different lifetimes. If you had an ensemble of identical particles, the probability of finding a given one of them still as they were - with no decay - after some time is given by the mathematical expression.

This governs what is known as the "decay rate. This makes different elements useful for different time scales of dating; an element with too short an average lifetime will have too few particles left to reveal much one way or another of potentially longer time scales.

Hence, elements such as potassium, which has an average lifetime of nearly 2 billion years before decaying into argon, are useful for very long time scales, with geological applications such as dating ancient lava flows or Martian rocks. Carbon, on the other hand, with a shorter mean lifetime of over years, is more useful for dating human artifacts. Atoms themselves consist of a heavy central core called the nucleus surrounded by arrangements of electron shells , wherein there are different probabilities of precisely locating a certain number of electrons depending on the element.

One way that a nucleus could be disrupted is by particles striking it. This interpretation unfortunately fails to consider observed energetic interactions, including that of the strong force, which is stronger the electromagnetic force.

## Earlham College - Geology - Radiometric Dating

It is important that the sample not have had any outside influences. One example of this can be found in metamorphic rocks. For example, with Uranium-lead dating with the crystallization of magma, this remains a closed system until the uranium decays. As it decays, it disrupts the crystal and allows the lead atom to move. Likewise, heating the rock such as granite forms gneiss or basalt forms schist. This can also disrupt the ratios of lead and uranium in the sample.

In order to calibrate radiometric dating methods, the methods need to be checked for accuracy against items with independently-known dates. Carbon dating, with its much lower maximum theoretical range, is often used for dating items only hundreds and thousands of years old, so can be calibrated in its lower ranges by comparing results with artifacts who's ages are known from historical records. Scientists have also attempted to extend the calibration range by comparing results to timber which has its age calculated by dendrochronology , but this has also been questioned because carbon dating is used to assist with working out dendrochronological ages.

Otherwise, calibration consists of comparing results with ages determined by other radiometric dating methods. However, tests of radiometric dating methods have often shown that they do not agree with known ages of rocks that have been seen to form from volcanic eruptions in recent and historic times, and there are also examples of radiometric dating methods not agreeing with each other. Young earth creationists therefore claim that radiometric dating methods are not reliable and can therefore not be used to disprove Biblical chronology.

Although radiometric dating methods are widely quoted by scientists , they are inappropriate for aging the entire universe due to likely variations in decay rates. Scientists insist that Earth is 4. A geological guidebook published by the Queensland government acknowledges that the dates are not absolute, but must be interpreted:.