Radiometric dating accuracy wiki
- Radiocarbon dating.
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Yes, radiometric dating is a very accurate way to date the Earth. We know it is accurate because radiometric dating is based on the radioactive decay of unstable isotopes. For example, the element Uranium exists as one of several isotopes, some of which are unstable. When an unstable Uranium U isotope decays, it turns into an isotope of the element Lead Pb. We call the original, unstable isotope Uranium the "parent", and the product of decay Lead the "daughter".
What is the accuracy of radiometric dating
From careful physics and chemistry experiments, we know that parents turn into daughters at a very consistent, predictable rate. A geologist can pick up a rock from a mountainside somewhere, and bring it back to the lab, and separate out the individual minerals that compose the rock. They can then look at a single mineral, and using an instrument called a mass spectrometer, they can measure the amount of parent and the amount of daughter in that mineral. The ratio of the parent to daughter then can be used to back-calculate the age of that rock.
The reason we know that radiometric dating works so well is because we can use several different isotope systems for example, Uranium-Lead, Lutetium-Halfnium, Potassium-Argon on the same rock, and they all come up with the same age. This gives geologists great confidence that the method correctly determines when that rock formed. Hope that helps, and please ask if you'd like more details! I think that I will start by answering the second part of your question, just because I think that will make the answer to the first question clearer. Radiometric dating is the use of radioactive and radiogenic those formed from the decay of radioactive parents isotopes isotopes are atoms of the same element that have different numbers of neutrons in their nuclei to determine the age of something.
It is commonly used in earth science to determine the age of rock formations or features or to figure out how fast geologic processes take place for example, how fast marine terraces on Santa Cruz island are being uplifted. Radiometric dating relies on the principle of radioactive decay. All radioactive isotopes have a characteristic half-life the amount of time that it takes for one half of the original number of atoms of that isotope to decay.
By measuring the parent isotope radioactive and the daughter isotope radiogenic in a system for example, a rock , we can tell how long the system has been closed in our example, when the rock formed. The process of radiogenic dating is usually done using some sort of mass spectrometer.
A mass spectrometer is an instrument that separates atoms based on their mass. Because geochronologists want to measure isotopes with different masses, a mass spectrometer works really well for dating things. I do think that radiometric dating is an accurate way to date the earth, although I am a geochronologist so I have my biases.
Most estimates of the age of the earth come from dating meteorites that have fallen to Earth because we think that they formed in our solar nebula very close to the time that the earth formed. The fact that the age we calculate is reproducible for these different systems is significant. We have also obtained a very similar age by measuring Pb isotopes in materials from earth.
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I should mention that the decay constants basically a value that indicates how fast a certain radioactive isotope will decay for some of these isotope systems were calculated by assuming that the age of the earth is 4. The decay constants for most of these systems have been confirmed in other ways, adding strength to our argument for the age of the earth. Radiometric dating depends on the chemistry and ratios of different elements.
Radiometric dating - RationalWiki
It works like this:. Take, for example, zircon, which is a mineral; its chemical formula is ZiSiO 4 , so there is one zirconium Zi for one silicon Si for four oxygen O. One of the elements that can stand in chemically for zircon is uranium. Uranium eventually decays into lead, and lead does not normally occur in zircon, except as the radioactive decay product of uranium. Therefore, by measuring the ratio of lead to uranium in a crystal of zircon, you can tell how much uranium there originally was in the crystal, which, combined with knowing the radioactive half-life of uranium, tells you how old the crystal is.
Obviously, if the substance you are measuring is contaminated, then all you know is the age since contamination, or worse, you don't know anything, because the contamination might be in the opposite direction - suppose, for example, you're looking at radio carbon carbon 14, which is produced in the atmosphere by cosmic rays, and which decays into nitrogen. Since you are exposed to the atmosphere and contain carbon, if you get oils from your skin onto an archeological artifact, then attempting to date it using radio carbon will fail because you are measuring the age of the oils on your skin, not the age of the artifact.
This is why crystals are good for radiometric dating: The oldest crystals on Earth that were formed on Earth are zircon crystals, and are approximately 4. Symbolically, the process of radioactive decay can be expressed by the following differential equation, where N is the quantity of decaying nuclei and k is a positive number called the exponential decay constant.
The meaning of this equation is that the rate of change of the number of nuclei over time is proportional only to the number of nuclei. This is consistent with the assumption that each decay event is independent and its chance does not vary over time. We can measure directly, for example by using a radiation detector, and obtain a good estimate of by analyzing the chemical composition of the sample. The half-life , specific to each nuclide, can be accurately measured on a pure sample, and is known to be independent of the chemical composition of the sample, temperature and pressure.
The half-life of carbon is approximately 5, years. Approximately how old is the bone? Thus the bone is approximately 17, years old. 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.
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.enter site
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. Indeed, special creationists have for many years held that where science and their religion conflict, it is a matter of science having to catch up with scripture, not the other way around. One way Young Earth Creationists and other denialists try to discredit radiometric dating is to cite examples radiometric dating techniques providing inaccurate results. This is frequently because the selected technique is used outside of its appropriate range, for example on very recent lavas. In attempting to date Mt. Helens, creationists attempted discredit the discipline through dishonest practices.