Learn something new every day More Info 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 process that determined the age of the Earth, a question that troubled scientists for centuries before finally reaching a largely accepted result in the 20th century. The discovery of radiometric dating is largely attributed to Ernest Rutherford, a British scientist who became interested in the study of radioactivity in the late 19th century.
The earth is billions of years old. The most useful methods for measuring the ages of geologic materials are the radiometric methods-the ones that make use of radioactive parent isotopes and their stable daughter products, as preserved in rocks, minerals, or other geologic materials. The main condition for the method is that the production rate of isotopes stays the same through . For many people, radiometric dating might be the one scientific technique that most blatantly seems to challenge the Bible's record of recent creation. For this reason, ICR research has long focused on the science behind these dating techniques. Sep 14, Here of some of the well-tested methods of dating used in the study of early humans: Potassium-argon dating, Argon-argon dating, Carbon (or Radiocarbon), and Uranium archotelzeeland.com of these methods measure the amount of radioactive decay of chemical elements; the decay occurs in a consistent manner, like a clock, over long periods of time.
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.
Table 2 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.
These flows buried and destroyed Pompeii and other nearby Roman cities. We know the exact day of this eruption because Pliny the Younger carefully recorded the event. They separated sanidine crystals from a sample of one of the ash flows. Incremental heating experiments on 12 samples of sanidine yielded 46 data points that resulted in an isochron age of 94 years.
The actual age of the flow in was years. Is this just a coincidence?
Some meteorites, because of their mineralogy, can be dated by more than one radiometric dating technique, which provides scientists with a powerful check of the validity of the results. The results from three meteorites are shown in Table 1. Many more, plus a discussion of the different types of meteorites and their origins, can be found in. 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. The absolute age of a wide variety of rocks, fossils, and human artifacts can be determined by various laboratory procedures. Deciding which test to perform depends on the composition and believed approximate age of a particular specimen. For example Carbon 14 is often the method of choice for scientists dating organic artifacts like wood, charcoal, bone, and teeth that are less .
No - it is the result of extremely careful analyses using a technique that works. This is not the only dating study to be done on an historic lava flow. Two extensive studies done more than 25 years ago involved analyzing the isotopic composition of argon in such flows to determine if the source of the argon was atmospheric, as must be assumed in K-Ar dating Dalrymple26 flows; Krummenacher19 flows. Both studies detected, in a few of the flows, deviations from atmospheric isotopic composition, most often in the form of excess 40 Ar.
A radiometric dating technique
The majority of flows, however, had no detectable excess 40 Ar and thus gave correct ages as expected. Of the handful of flows that did contain excess 40 Ar, only a few did so in significant amounts. Note, however, that even an error of 0. Austin has documented excess 40 Ar in the dacite flow from Mount St Helens, but the amounts are insufficient to produce significant errors in all but the youngest rocks.
Thus any potential error due to excess 40 Ar was eliminated by the use of this technique, which was not available when the studies by Dalrymple and Krummenacher were done.
Radiometric Dating: Definition, How Does it Work, Uses & Examples
Thus the large majority of historic lava flows that have been studied either give correct ages, as expected, or have quantities of excess radiogenic 40 Ar that would be insignificant in all but the youngest rocks. In this short paper I have briefly described 4 examples of radiometric dating studies where there is both internal and independent evidence that the results have yielded valid ages for significant geologic events.
It is these studies, and the many more like them documented in the scientific literature, that the creationists need to address before they can discredit radiometric dating. Their odds of success are near zero. Even if against all odds they should succeed, it still would not prove that the Earth is young.
Only when young-earth creationists produce convincing quantitative, scientific evidence that the earth is young will they be worth listening to on this important scientific matter. I thank Chris Stassen and 2 anonymous reviewers for their thoughtful comments, which led to important improvements in the manuscript. Make a Donation Today. Give a Gift Membership.
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Radiometric Dating: How Does It Work?
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The Ages of Meteorites Meteorites, most of which are fragments of asteroids, are very interesting objects to study because they provide important evidence about the age, composition, and history of the early solar system.
The K-T Tektites 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. Summary In this short paper I have briefly described 4 examples of radiometric dating studies where there is both internal and independent evidence that the results have yielded valid ages for significant geologic events.
Acknowledgments I thank Chris Stassen and 2 anonymous reviewers for their thoughtful comments, which led to important improvements in the manuscript. Uranium-thorium datingalso called thorium datinguranium-series disequilibrium dating or uranium-series datingis a radiometric dating technique established in the s which has been used since the s to determine the age of calcium carbonate materials such as speleothem or coral.
Instead, it calculates an age from the degree to which secular equilibrium has been restored between the radioactive isotope thorium and its radioactive parent uranium within a sample. Thorium is not soluble in natural water under conditions found at or near the surface of the earth, so materials grown in or from this water do not usually contain thorium.
As time passes after such material has formed, uranium in the sample with a half-life ofyears decays to thorium At secular equilibrium, the number of thorium decays per year within a sample is equal to the number of thorium produced, which also equals the number of uranium decays per year in the same sample.
InJohn Jolya professor of geology from the University of Dublinfound higher radium contents in deep sediments than in those of the continental shelf, and suspected that detrital sediments scavenged radium out of seawater. Piggot and Urry found inthat radium excess corresponded with an excess of thorium. It took another 20 years until the technique was applied to terrestrial carbonates speleothems and travertines. In the late s the method was refined by mass spectrometry.
After Viktor Viktorovich Cherdyntsev 's landmark book about uranium had been translated into English, U-Th dating came to widespread research attention in Western geology.
U-series dating is a family of methods which can be applied to different materials over different time ranges. Each method is named after the isotopes measured to obtain the date, mostly a daughter and its parent.
Eight methods are listed in the table below. Using this technique to calculate an age, the ratio of uranium to its parent isotope uranium must also be measured.
U-Th dating yields the most accurate results if applied to precipitated calcium carbonate, that is in stalagmitestravertines, and lacustrine limestones. Bone and shell are less reliable.