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Radiometric dating - Wikipedia

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See also Counterexamples to an Old Earth. Radiometric dating is a method of determining the age of an artifact by assuming that on average decay rates have been constant see below for the flaws in that assumption and measuring the amount of radioactive decay that has occurred. Because radiometric dating fails to satisfy standards of testability and falsifiability , claims based on radiometric dating may fail to qualify under the Daubert standard for court-admissible scientific evidence. It is more accurate for shorter time periods e. There are a number of implausible assumptions involved in radiometric dating with respect to long time periods. One key assumption is that the initial quantity of the parent element can be determined.

Radiometric datingradioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbonin which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.

Together with stratigraphic principlesradiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.

Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

All ordinary matter is made up of combinations of chemical elementseach with its own atomic numberindicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopeswith each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of a particular element is called a nuclide. Some nuclides are inherently unstable.

That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide.

This transformation may be accomplished in a number of different ways, including alpha decay emission of alpha particles and beta decay electron emission, positron emission, or electron capture.

Another possibility is spontaneous fission into two or more nuclides. While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-lifeusually given in units of years when discussing dating techniques. After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide or decay product.

In many cases, the daughter nuclide itself is radioactive, resulting in a decay chaineventually ending with the formation of a stable nonradioactive daughter nuclide; each step in such a chain is characterized by a distinct half-life. In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter.

Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years e. For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant. It is not affected by external factors such as temperaturepressurechemical environment, or presence of a magnetic or electric field. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time.

This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present. The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation.

The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created. It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.

Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. This can reduce the problem of contamination. In uranium—lead datingthe concordia diagram is used which also decreases the problem of nuclide loss.

Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3. Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement except as described below under "Dating with short-lived extinct radionuclides"the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material.

The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate. This normally involves isotope-ratio mass spectrometry. The precision of a dating method depends in part on the half-life of the radioactive isotope involved.

How Does Radiocarbon Dating Work? - Instant Egghead #28

For instance, carbon has a half-life of 5, years. After an organism has been dead for 60, years, so little carbon is left that accurate dating cannot be established. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades.

If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusionsetting the isotopic "clock" to zero. The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system.

These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.

This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature.

The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature. This field is known as thermochronology or thermochronometry.

The mathematical expression that relates radioactive decay to geologic time is [12] [15]. The equation is most conveniently expressed in terms of the measured quantity N t rather than the constant initial value N o. The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature.

This is well-established for most isotopic systems. Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition. Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth. In the century since then the techniques have been greatly improved and expanded.

The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization.

On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams. Uranium—lead radiometric dating involves using uranium or uranium to date a substance's absolute age.

Radiometric dating depends on the decay of isotopes, which are different Isotopes are different versions of the same element (e.g., carbon. Com. Define the experimental outcome derived from antarctica. In brief relative age dating. Many ancient lava flows are most rocks are obtained with different. Radiometric dating is any method of age determination which is based on radioactive decay. There are several with different strengths and weaknesses.

This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. Uranium—lead dating is often performed on the mineral zircon ZrSiO 4though it can be used on other materials, such as baddeleyiteas well as monazite see: monazite geochronology. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert.

Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. One of its great advantages is that any sample provides two clocks, one based on uranium's decay to lead with a half-life of about million years, and one based on uranium's decay to lead with a half-life of about 4.

This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample.

This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1. This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years.

This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples. Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years.

It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured. The scheme has a range of several hundred thousand years. A related method is ionium—thorium datingwhich measures the ratio of ionium thorium to thorium in ocean sediment. Radiocarbon dating is also simply called carbon dating.

Carbon is a radioactive isotope of carbon, with a half-life of 5, years [25] [26] which is very short compared with the above isotopesand decays into nitrogen. Carbon, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon ends up as a trace component in atmospheric carbon dioxide CO 2.

A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesisand animals acquire it from consumption of plants and other animals.

When an organism dies, it ceases to take in new carbon, and the existing isotope decays with a characteristic half-life years. The proportion of carbon left when the remains of the organism are examined provides an indication of the time elapsed since its death.

Radioactive decay and radiometric dating difference - Register and search over 40 million singles: chat. Join the leader in online dating services and find a date. Various elements are used for dating different time periods; ones with relatively short half-lives like carbon (or. Radiometric dating is the technique of using isotopic ratios of common The ratio of the difference is related mathematically to the time that is.

This makes carbon an ideal dating method to date the age of bones or the remains of an organism. The carbon dating limit lies around 58, to 62, years. The rate of creation of carbon appears to be roughly constant, as cross-checks of carbon dating with other dating methods show it gives consistent results. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon and give inaccurate dates.

The releases of carbon dioxide into the biosphere as a consequence of industrialization have also depressed the proportion of carbon by a few percent; conversely, the amount of carbon was increased by above-ground nuclear bomb tests that were conducted into the early s. Also, an increase in the solar wind or the Earth's magnetic field above the current value would depress the amount of carbon created in the atmosphere.

This involves inspection of a polished slice of a material to determine the density of "track" markings left in it by the spontaneous fission of uranium impurities.

Radioactive dating and radiometric dating difference

The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons. This causes induced fission of U, as opposed to the spontaneous fission of U. The fission tracks produced by this process are recorded in the plastic film. The uranium content of the material can then be calculated from the number of tracks and the neutron flux.

This scheme has application over a wide range of geologic dates. For dates up to a few million years micastektites glass fragments from volcanic eruptionsand meteorites are best used. Older materials can be dated using zirconapatitetitaniteepidote and garnet which have a variable amount of uranium content. The technique has potential applications for detailing the thermal history of a deposit. The residence time of 36 Cl in the atmosphere is about 1 week.

Thus, as an event marker of s water in soil and ground water, 36 Cl is also useful for dating waters less than 50 years before the present.

Luminescence dating methods are not radiometric dating methods in that they do not rely on abundances of isotopes to calculate age. Another assumption is that the rate of decay is constant over long periods of time.

Radiometric dating requires that the decay rates of the isotopes involved be accurately known, and that there is confidence that these decay rates are constant. Fortunately, this is the case.

The physical constants nucleon masses, fine structure constant involved in radioactive decay are well characterized, and the processes are well understood. Careful astronomical observations show that the constants have not changed significantly in billions of years—spectral lines from distant galaxies would have shifted perceptibly if these constants had changed.

In some cases radioactive decay itself can be observed and measured in distant galaxies when a supernova explodes and ejects unstable nuclei. There are a few effects that can alter radioactive half-lives, but they are mostly well understood, and in any case would not materially affect the radiometric dating results. That is, the analysis of the isotopic and chemical composition of the sample has far greater uncertainty than any uncertainty in the decay rate itself.

The major reason that decay rates can change is that the electric field, from the atom's electron cloud, can change due to chemical changes. That is, electrons can move closer to or farther away from the nucleus depending on the chemical bonds.

This affects the coulomb barrier involved in Alpha decayand therefore changes the height and width of the barrier through which the alpha particle must tunnel. The effect of this on alpha decay, which is the most common decay mode in radiometric dating, is utterly insignificant.

How does radioactive decay relate to radiometric dating?

There is another effect that takes place in the "electron capture" type of Beta decay. This is an example of the Weak forceand is fairly rare. Electron capture requires that there be an electron in the vicinity of the nucleus, so its activity depends strongly on the configuration of the electron cloud, which depends on the chemical state.

In fact, it is possible to shut down electron capture completely—simply ionize the substance so that there are no electrons nearby. There is a fairly well-known example of chemical state affecting electron capture activity. The 7 Be nucleus Beryllium-7 is an electron capturer with a half-life of about 53 days, turning into Lithium The variation is about 1. While this half-life is way too short to be useful for radiometric dating, the effect of the chemical state is noticeable.

The reason is that, because the atomic number is only four, the 2s valence electrons are very close to the 1s electrons involved in capture.

Radiometric dating

There is no reason to expect that the rate of decay of a radioactive material is largely constant, [4] and it was almost certainly not constant near the creation or beginning of the universe. As early as ofJohn 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".

Atoms consist of a heavy central core called the nucleus surrounded by clouds of lightweight particles electronscalled 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.

Those that can decay are mesons and baryonswhich include protons and neutrons ; although decays can involve other particles such as photonselectronspositronsand neutrinos.

Radiometric dating is used to estimate the age of rocks and other objects it is used in different dating methods, such as uranium-lead dating and radiocarbon. Radiometric dating is mostly used to determine the age of rocks, though a particular form of radiometric dating—called Radiocarbon dating—can date wood , . The rate is unique to different particles and so to different atomic. Additionally, elements may exist in different isotopes, with each an atom of such a nuclide will undergo radioactive decay.

This can happen due to one of three forces or "interactions": strong, electromagnetic, and weak, in order of decreasing strength. 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.

A complex set of rules describes the details of particle decays: historically, the finding of which as been a major objective of particle physics. 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 shellswherein 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. 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 dendrochronologybut 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 scientiststhey 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:. One example of scientists not accepting radiometric dates is that of Mungo Mana human fossil from New South Wales.

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