Radioactive dating vs carbon dating
Potassium is a component in many common minerals and can be used to determine the ages of igneous and metamorphic rocks. The Potassium-Argon dating method is the measurement of the accumulation of Argon in a mineral. It is based on the occurrence of a small fixed amount of the radioisotope 40 K in natural potassium that decays to the stable Argon isotope 40 Ar with a half-life of about 1, million years. In contrast to a method such as Radiocarbon dating, which measures the disappearance of a substance, K-Ar dating measures the accumulation of Argon in a substance from the decomposition of potassium.
Argon, being an inert gas, usually does not leech out of a mineral and is easy to measure in small samples. This method dates the formation or time of crystallisation of the mineral that is being dated; it does not tell when the elements themselves were formed. It is best used with rocks that contain minerals that crystallised over a very short period, possibly at the same time the rock was formed.
Radiometric dating - RationalWiki
This method should also be applied only to minerals that remained in a closed system with no loss or gain of the parent or daughter isotope. Uranium-Lead U-Pb dating is the most reliable method for dating Quaternary sedimentary carbonate and silica, and fossils particulary outside the range of radiocarbon.
Quaternary geology provides a record of climate change and geologically recent changes in environment. U-Pb geochronology of zircon , baddelyite , and monazite is used for determining the age of emplacement of igneous rocks of all compositions, ranging in age from Tertiary to Early Archean. U-Pb ages of metamorphic minerals, such as zircon or monazite are used to date thermal events, including terrestrial meteoritic impacts. U-Pb ages of zircon in sediments are used to determine the provenance of the sediments.
The Fission track analysis is based on radiation damage tracks due to the spontaneous fission of U. Fission-tracks are preserved in minerals that contain small amounts of uranium, such as apatite and zircon. Fission-track analysis is useful in determining the thermal history of a sample or region. By determining the number of tracks present on a polished surface of a grain and the amount of uranium present in the grain, it is possible to calculate how long it took to produce the number of tracks preserved.
As long as the mineral has remained cool, near the earth surface, the tracks will accumulate. If the rock containing these minerals is heated, the tracks will begin to disappear. The tracks will then begin to accumulate when the rock begins to cool. If a rock cools quickly as in the case of a volcanic rock or a shallow igneous intrusion, the fission-track ages will date this initial cooling. 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.
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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. 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.
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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,  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".
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. 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.
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. Our input data had two significant figures, so reporting a more accurate result would be meaningless.
This is based on the decay of rubidium isotopes to strontium isotopes, and can be used to date rocks or to relate organisms to the rocks on which they formed. It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation. This method for rock dating is based on the decay of potassium into argon: One problem is that potassium is also highly mobile and may move into older rocks.
This depends on the decay of uranium and uranium to isotopes of lead. Due to the long half-life of uranium it is not suitable for short time periods, such as most archaeological purposes, but it can date the oldest rocks on earth. A important limitation of radiometric dating often overlooked by layman and not always made clear in scholarly works as well is that any date is actually a range, following the 68—95— This leaves out important information which would tell you how precise is the dating result. Carbon dating has an interesting limitation in that the ratio of regular carbon to carbon in the air is not constant and therefore any date must be calibrated using dendrochronology.
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Another limitation is that carbon can only tell you when something was last alive, not when it was used. A limitation with all forms of radiometric dating is that they depend on the presence of certain elements in the substance to be dated. Carbon dating works on organic matter, all of which contains carbon. However it is less useful for dating metal or other inorganic objects. Most rocks contain uranium, allowing uranium-lead and similar methods to date them. Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.
Note that although carbon dating receives a lot of attention, since it can give information about the relatively recent past, it is rarely used in geology and almost never used to date fossils. Carbon decays almost completely within , years of the organism dying, and many fossils and rock strata are hundreds of times older than that. To date older fossils, other methods are used, such as potassium-argon or argon-argon dating. Other forms of dating based on reactive minerals like rubidium or potassium can date older finds including fossils, but have the limitation that it is easy for ions to move into rocks post-formation so that care must be taken to consider geology and other factors.
Radiometric dating — through processes similar to those outlined in the example problem above — frequently reveals that rocks, fossils , etc. The oldest rock so far dated is a zircon crystal that formed 4. They tie themselves in logical knots trying to reconcile the results of radiometric dating with the unwavering belief that the Earth was created ex nihilo about 6, to 10, years ago. Creationists often blame contamination.