How do we determine the age of a rock?
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What is an application of nuclear chemistry in medicine? What is an application of nuclear chemistry in agriculture? What is neutron activation analysis? What does nuclear medicine diagnose? What is a nuclear imaging of the heart? What does radioactive dating enable geologists to determine? For example, uranium-lead dating can be used to find the age of a uranium-containing mineral. It works because we know the fixed radioactive decay rates of uranium, which decays to lead, and for uranium, which decays to lead So, we start out with two isotopes of uranium that are unstable and radioactive.
They release radiation until they eventually become stable isotopes of lead.
Radiometric Dating Does Work!
These two uranium isotopes decay at different rates. In other words, they have different half-lives. The half-life of the uranium to lead is 4. The uranium to lead decay series is marked by a half-life of million years. These differing rates of decay help make uranium-lead dating one of the most reliable methods of radiometric dating because they provide two different decay clocks. This provides a built-in cross-check to more accurately determine the age of the sample. Uranium is not the only isotope that can be used to date rocks; we do see additional methods of radiometric dating based on the decay of different isotopes.
For example, with potassium-argon dating , we can tell the age of materials that contain potassium because we know that potassium decays into argon with a half-life of 1. With rubidium-strontium dating , we see that rubidium decays into strontium with a half-life of 50 billion years. By anyone's standards, 50 billion years is a long time. In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon.
So, we see there are a number of different methods for dating rocks and other non-living things, but what if our sample is organic in nature? For example, how do we know that the Iceman, whose frozen body was chipped out of glacial ice in , is 5, years old? Well, we know this because samples of his bones and hair and even his grass boots and leather belongings were subjected to radiocarbon dating.
Radiocarbon dating , also known as carbon dating or simply carbon dating, is a method used to determine the age of organic material by measuring the radioactivity of its carbon content. So, radiocarbon dating can be used to find the age of things that were once alive, like the Iceman. And this would also include things like trees and plants, which give us paper and cloth.
So, radiocarbon dating is also useful for determining the age of relics, such the Dead Sea Scrolls and the Shroud of Turin. With radiocarbon dating, the amount of the radioactive isotope carbon is measured. Compared to some of the other radioactive isotopes we have discussed, carbon's half-life of 5, years is considerably shorter, as it decays into nitrogen Carbon is continually being created in the atmosphere due to the action of cosmic rays on nitrogen in the air. Carbon combines with oxygen to create carbon dioxide.
Because plants use carbon dioxide for photosynthesis, this isotope ends up inside the plant, and because animals eat plants, they get some as well. When a plant or an animal dies, it stops taking in carbon The existing carbon within the organism starts to decay back into nitrogen, and this starts our clock for radiocarbon dating. A scientist can take a sample of an organic material when it is discovered and evaluate the proportion of carbon left in the relic to determine its age. Radiometric dating is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.
The decay rate is referring to radioactive decay , which is the process by which an unstable atomic nucleus loses energy by releasing radiation. Each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life or, in other words, the time required for a quantity to fall to half of its starting value. There are different methods of radiometric dating.
Uranium-lead dating can be used to find the age of a uranium-containing mineral.
Radiometric dating - Wikipedia
Uranium decays to lead, and uranium decays to lead The two uranium isotopes decay at different rates, and this helps make uranium-lead dating one of the most reliable methods because it provides a built-in cross-check. Additional methods of radiometric dating, such as potassium-argon dating and rubidium-strontium dating , exist based on the decay of those isotopes. Radiocarbon dating is a method used to determine the age of organic material by measuring the radioactivity of its carbon content.
With radiocarbon dating, we see that carbon decays to nitrogen and has a half-life of 5, years. To unlock this lesson you must be a Study. Did you know… We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities. You can test out of the first two years of college and save thousands off your degree.
Anyone can earn credit-by-exam regardless of age or education level. To learn more, visit our Earning Credit Page. Not sure what college you want to attend yet? The videos on Study. Students in online learning conditions performed better than those receiving face-to-face instruction. Explore over 4, video courses. Find a degree that fits your goals. Learn about half-life and how it is used in different dating methods, such as uranium-lead dating and radiocarbon dating, in this video lesson.
The first is that each meteorite was dated by more than one laboratory — Allende by 2 laboratories, Guarena by 2 laboratories, and St Severin by four laboratories. This pretty much eliminates any significant laboratory biases or any major analytical mistakes. The second thing is that some of the results have been repeated using the same technique, which is another check against analytical errors. The third is that all three meteorites were dated by more than one method — two methods each for Allende and Guarena, and four methods for St Severin.
This is extremely powerful verification of the validity of both the theory and practice of radiometric dating. In the case of St Severin, for example, we have 4 different natural clocks actually 5, for the Pb-Pb method involves 2 different radioactive uranium isotopes , each running at a different rate and each using elements that respond to chemical and physical conditions in much different ways. And yet, they all give the same result to within a few percent.
Is this a remarkable coincidence? Scientists have concluded that it is not; it is instead a consequence of the fact that radiometric dating actually works and works quite well. Creationists who wants to dispute the conclusion that primitive meteorites, and therefore the solar system, are about 4. One of the most exciting and important scientific findings in decades was the discovery that a large asteroid, about 10 kilometers diameter, struck the earth at the end of the Cretaceous Period.
Radiometric Dating
The collision threw many tons of debris into the atmosphere and possibly led to the extinction of the dinosaurs and many other life forms. The fallout from this enormous impact, including shocked quartz and high concentrations of the element iridium, has been found in sedimentary rocks at more than locations worldwide at the precise stratigraphic location of the Cretaceous-Tertiary K-T boundary Alvarez and Asaro ; Alvarez We now know that the impact site is located on the Yucatan Peninsula.
Measuring the age of this impact event independently of the stratigraphic evidence is an obvious test for radiometric methods, and a number of scientists in laboratories around the world set to work. In addition to shocked quartz grains and high concentrations of iridium, the K-T impact produced tektites, which are small glass spherules that form from rock that is instantaneously melted by a large impact. The K-T tektites were ejected into the atmosphere and deposited some distance away.
Tektites are easily recognizable and form in no other way, so the discovery of a sedimentary bed the Beloc Formation in Haiti that contained tektites and that, from fossil evidence, coincided with the K-T boundary provided an obvious candidate for dating. Scientists from the US Geological Survey were the first to obtain radiometric ages for the tektites and laboratories in Berkeley, Stanford, Canada, and France soon followed suit.
The results from all of the laboratories were remarkably consistent with the measured ages ranging only from Similar tektites were also found in Mexico, and the Berkeley lab found that they were the same age as the Haiti tektites. The K-T boundary is recorded in numerous sedimentary beds around the world. Numerous thin beds of volcanic ash occur within these coals just centimeters above the K-T boundary, and some of these ash beds contain minerals that can be dated radiometrically.
Since both the ash beds and the tektites occur either at or very near the K-T boundary, as determined by diagnostic fossils, the tektites and the ash beds should be very nearly the same age, and they are Table 2. There are several important things to note about these results. First, the Cretaceous and Tertiary periods were defined by geologists in the early s.
The boundary between these periods the K-T boundary is marked by an abrupt change in fossils found in sedimentary rocks worldwide. Its exact location in the stratigraphic column at any locality has nothing to do with radiometric dating — it is located by careful study of the fossils and the rocks that contain them, and nothing more. Furthermore, the dating was done in 6 different laboratories and the materials were collected from 5 different locations in the Western Hemisphere. And yet the results are the same within analytical error. In the early afternoon of August 24, 79 CE, Mt Vesuvius erupted violently, sending hot ash flows speeding down its flanks.