Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in 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. The use of radiometric dating was first published in by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of the Earth itself, and can also be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. 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.
To understand radiometric dating techniquesyou first have to have an understanding of what is being measured, how the measurement is being made and the theoretical as well as practical limitations of the system of measurement being used.
As an analogy, say you find yourself wondering, "How warm or cold is it outside? You need a device to measure this activity a thermometer, of which various kinds exist.
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. radiometric dating. [ ra?de-o-met ?rik ] A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products (in this case strontium).
You also need to know when you can or cannot apply a particular type of device to the task at hand; for example, if you want to know how hot it is on the inside of an active wood stove, you probably understand that putting a household thermometer intended to measure body temperature inside the stove is not going to prove helpful. Be aware also that for many centuries, most human "knowledge" of the age of rocks, formations such as the Grand Canyon, and everything else around you was predicated on the Genesis account of the Bible, which posits that the entire cosmos is perhaps 10, years old.
Modern geological methods have at times proven thorny in the face of such popular but quaint and scientifically unsupported notions.
Radiometric dating takes advantage of the fact that the composition of certain minerals rocks, fossils and other highly durable objects changes over time. Specifically, the relative amounts of their constituent elements shift in a mathematically predictable way thanks to a phenomenon called radioactive decay.
This in turn relies on knowledge of isotopessome of which are "radioactive" that is, they spontaneously emit subatomic particles at a known rate. Isotopes are different versions of the same element e. Some things in nature disappear at a more or less constant rate, regardless of how much there is to start with and how much remains.
May 12, Radiometric dating is a method by which the age of materials such as rocks can be determined. The process relies on the fact that certain atoms decay or transform at a measurable rate over time, meaning that age can be established by working out the rate of decay from a sample. The invention of radiometric dating was a crucial step in the. Radiometric dating is a means of determining the age of very old objects, including the Earth itself. Radiometric dating depends on the decay of isotopes, which are different forms of the same element that include the same number of protons but different numbers of neutrons in their atoms. radiometric dating. (ra?de-o-met?rik) A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. The amount of the isotope in the object is compared to the amount of the isotope's decay products. The object's approximate age can then be figured out using the known rate of decay of the isotope.
For example, certain drugs, including ethyl alcohol, are metabolized by the body at a fixed number of grams per hour or whatever units are most convenient.
If someone has the equivalent of five drinks in his system, the body takes five times as long to clear the alcohol as it would if he had one drink in his system. Many substances, however, both biological and chemical, conform to a different mechanism: In a given time period, half of the substance will disappear in a fixed time no matter how much is present to start with.
Radiometric dating meaning science
Such substances are said to have a half-life. Radioactive isotopes obey this principle, and they have wildly different decay rates.
The utility of this lies in being able to calculate with ease how much of a given element was present at the time it was formed based on how much is present at the time of measurement. This is because when radioactive elements first come into being, they are presumed to consist entirely of a single isotope. As radioactive decay occurs over time, more and more of this most common isotope "decays" i.
Imagine that you enjoy a certain kind of ice cream flavored with chocolate chips. You have a sneaky, but not especially clever, roommate who doesn't like the ice cream itself, but cannot resist picking out eating the chips - and in an effort to avoid detection, he replaces each one he consumes with a raisin.
He is afraid to do this with all of the chocolate chips, so instead, each day, he swipes half of the number of remaining chocolate chips and puts raisins in their place, never quite completing his diabolical transformation of your dessert, but getting closer and closer. Say a second friend who is aware of this arrangement visits and notices that your carton of ice cream contains 70 raisins and 10 chocolate chips.
She declares, "I guess you went shopping about three days ago.
Because your roommate eats half of the chips on any given day, and not a fixed number, the carton must have held 20 chips the day before, 40 the day before that, and 80 the day before that. Calculations involving radioactive isotopes are more formal but follow the same basic principle: If you know the half-life of the radioactive element and can measure how much of each isotope is present, you can figure out the age of the fossil, rock or other entity it comes from.
Elements that have half-lives are said to obey a first-order decay process. They have what is known as a rate constant, usually denoted by k.
The relationship between the number of atoms present at the start N 0the number present at the time of measurement N the elapsed time t, and the rate constant k can be written in two mathematically equivalent ways:. In addition, you may wish to know the activity A of a sample, typically measured in disintegrations per second or dps.
This is expressed simply as:.
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You don't need to know how these equations are derived, but you should be prepared to use them so solve problems involving radioactive isotopes. Scientists interested in figuring out the age of a fossil or rock analyze a sample to determine the ratio of a given radioactive element's daughter isotope or isotopes to its parent isotope in that sample.
With the element's decay rate, and hence its half-life, known in advance, calculating its age is straightforward. The trick is knowing which of the various common radioactive isotopes to look for.
This in turn depends in the approximate expected age of the object because radioactive elements decay at enormously different rates. Also, not all objects to be dated will have each of the elements commonly used; you can only date items with a given dating technique if they include the needed compound or compounds.
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Uranium-lead U-Pb dating: Radioactive uranium comes in two forms, uranium and uranium The number refers to the number of protons plus neutrons. Uranium's atomic number is 92, corresponding to its number of protons.
Also called radioactive dating. Origin of radiometric dating First recorded in - Words nearby radiometric dating radioluminescenceradiolysisradiomanradiometeorographradiometerradiometric datingradiomicrometerradiomimeticradionecrosisradioneuritisradionics.
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Words related to radiometric dating datingthermoluminescence. A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it.
How Does Radiometric Dating Work? - Ars Technica
For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products in this case strontium.