What Is Radioactive Dating, and How Does It Work?
Radiocarbon dating works by comparing the three different isotopes of carbon. Isotopes of a particular element have the same number of. Radiometric dating (often called radioactive dating) is a technique used to date materials such as rocks or carbon, usually based on a. Some so-called creation scientists have attempted to show that radiometric dating does not work on theoretical grounds (for example, Arndts and Overn ;.
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 isotopeseach 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.
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. 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.
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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.Creation v. Evolution: How Carbon Dating Works
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. 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.
Radiometric Dating Does Work!
The actual age of the flow in was years. Is this just a coincidence? 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.
Note, however, that even an error of 0. 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. 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.
Acknowledgments I thank Chris Stassen and 2 anonymous reviewers for their thoughtful comments, which led to important improvements in the manuscript. T Rex and the Crater of Doom. Alvarez W, Asaro, F. Arndts R, Overn W. Excess argon within mineral concentrates from the new dacite lava dome at Mount St Helens volcano.
How old is the earth? A reply to scientific creationism.
Awbrey F, Thwaites WM, editors. The Age of the Earth. Stanford, Stanford University Press, US Geological Survey Bulletin A sufficient reason for false Rb-Sr isochrons. Isotopic composition of argon in modern surface volcanic rocks. Calibration against Pliny the Younger.
Rugg S, Austin SA. Creation Science Fellowship, Over time 14C decays to nitrogen 14N. Most 14C is produced in the upper atmosphere where neutrons, which are produced by cosmic raysreact with 14N atoms. This CO2 is used in photosynthesis by plants, and from here is passed through the food chain see figure 1, below.
Every plant and animal in this chain including us!
Radiometric Dating: Methods, Uses & the Significance of Half-Life
Dating history When living things die, tissue is no longer being replaced and the radioactive decay of 14C becomes apparent.
Around 55, years later, so much 14C has decayed that what remains can no longer be measured. In 5, years half of the 14C in a sample will decay see figure 1, below. Therefore, if we know the 14C: Unfortunately, neither are straightforward to determine. Carbon dioxide is used in photosynthesis by plants, and from here is passed through the food chain.
The amount of 14C in the atmosphere, and therefore in plants and animals, has not always been constant. For instance, the amount varies according to how many cosmic rays reach Earth. Luckily, we can measure these fluctuations in samples that are dated by other methods.
Tree rings can be counted and their radiocarbon content measured.
Radiometric dating - Wikipedia
A huge amount of work is currently underway to extend and improve the calibration curve. In we could only calibrate radiocarbon dates until 26, years.
Now the curve extends tentatively to 50, years. Dating advances Radiocarbon dates are presented in two ways because of this complication. The uncalibrated date is given with the unit BP radiocarbon years before The calibrated date is also presented, either in BC or AD or with the unit calBP calibrated before present - before The second difficulty arises from the extremely low abundance of 14C.
Many labs now use an Accelerator Mass Spectrometer AMSa machine that can detect and measure the presence of different isotopes, to count the individual 14C atoms in a sample. Australia has two machines dedicated to radiocarbon analysis, and they are out of reach for much of the developing world. In addition, samples need to be thoroughly cleaned to remove carbon contamination from glues and soil before dating. This is particularly important for very old samples.