Radiometric dating of rocks and minerals using naturally occurring, long-lived radioactive isotopes is troublesome for young-earth creationists because the techniques have provided overwhelming evidence of the antiquity of the earth and life. Some so-called creation scientists have attempted to show that radiometric dating does not work on theoretical grounds for example, Arndts and Overn ; Gill but such attempts invariably have fatal flaws see Dalrymple ; York and Dalrymple Other creationists have focused on instances in which radiometric dating seems to yield incorrect results. In most instances, these efforts are flawed because the authors have misunderstood or misrepresented the data they attempt to analyze for example, Woodmorappe ; Morris HM ; Morris JD Only rarely does a creationist actually find an incorrect radiometric result Austin ; Rugg and Austin that has not already been revealed and discussed in the scientific literature. The creationist approach of focusing on examples where radiometric dating yields incorrect results is a curious one for two reasons.
The slope of the line gives the age of the rock.
Unlike other isochrons, the slope of the Pb-Pb isochron decreases with increasing age. This is because U has a half-life of million years, while U has a half-life of 4. The rate at which daughter isotopes accumulate is dependent on the amount of parent isotope present. Since U has a much shorter half-life, a larger fraction of the initial U present in the rock will have decayed compared to U.
Other parts of isotope clock dating to determine the invention of a single. Thus fission track dating techniques, and dating of the pierre shale, of meteorite. Methods of scientists have already been determined with the manson meteorite and billion years old. Accompanies the age may represent the canyon diablo iron meteorite. Because of their importance, meteorites have been extensively dated radiometrically; the vast majority appear to be - Ga (billion years) old. 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. Clocks in the Rocks. The following radioactive decay processes have proven particularly useful in radioactive dating for geologic processes. Lead isochrons are also an important radioactive dating process. Note that uranium and uranium give rise to two of the natural radioactive series, but rubidium and potassium do not give rise to series. They each stop with a single.
Therefore, Pb will accumulate at a slower rate than Pb, causing the isochron to decrease in slope with increasing age. The use of lead isotope ratios makes this isochron self-checking.
A large scattering of measurements would indicate the sample is multi-stage rather than single-stage, making the isochron unreliable. Another situation in which single-stage systems give unreliable information is the extraction of lead from uranium to form lead ore. It is possible that a system could undergo a geological process that extracts lead, leaving the new system without any uranium.
If that system were dated at that point in time, it would fall on the isochron and give the correct age of the mineral. However, without any uranium present, accumulation of daughter isotopes ceases even though time continues to pass. Such events produce a frozen record, giving the amount of time from crystallization to extraction of lead to form lead ore. Such ages are very useful because they can measure time forward from some known event in the past, such as the formation of the earth.
The difficulties with single-stage systems can be circumnavigated with multi-stage systems. Though multi-stage lead samples cannot be used for generating isochrons, they can be used to produce valuable information through concordia-discordia plots. These plots are also self-checking and are useful for dating old rocks with complex histories.
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The plots can still produce valuable and accurate data using rocks that have been subjected to heating and metamorphic events Dalrymple This utility is due to the fact that the concordia-discordia method uses the simultaneous decay of U to Pb and U to Pb to tabulate age.
A sample concordia diagram from Dalrymple is shown in Figure 4.
The change in ratios of parent to daughter isotopes over time is used to construct an age curve called a concordia. Since lead loss from a mineral does not fractionate the isotopes, the resulting change in parent to daughter isotope ratios will fall on a line called discordia, which connects the original age on concordia to the age on concordia of lead loss.
This method requires minerals that contain either no initial lead or negligible amounts of initial lead, but some such minerals can be found in igneous and metamorphic rocks Dalrymple An isotope of Rb decays into Sr over known amounts of time, so by measuring both Rb and Sr, we can determine how much time has passed since the rock formed.
Scientists typically determine the age of a rock or meteorite by using the isochron method. For purposes of illustration, consider the rubidium-strontium decay system. In this system, the radioactive parent rubidium (87 Rb) decays to the stable daughter isotope strontium (87 Sr). The half-life for 87 Rb decay is billion years. meteorite dating is solely based on its production by cosmic rays (and for terrestrial samples, with its production in the atmosphere). 26Al and some other nuclides not mentioned are also used in this way. Thus, although "extinct", these nuclides are present in meteorites, but produced by a . Therefore, the most precise dating method for these meteorites is the Pb-Pb method, which allows a correction for common Pb. When the abundance of Pb is relatively low, this isotope has larger measurement errors than the other Pb isotopes, leading to very strong correlation of errors between the measured ratios.
While radioactivity is a standard technique for dating samples on Earth, few other places in the solar system have been dated this way. Instead, scientists have largely constrained the chronology of the inner solar system by counting impact craters on planetary surfaces. It's undoubtedly true.
But as with the falling rain, we don't really know the rate at which meteorites have fallen from the sky.
That's why radioisotope dating is so important. Radioactive decay is a clock that ticks at a known rate. These techniques accurately determine the ages of rocks and minerals, allowing scientists to date events such as crystallization, metamorphism and impacts.
This precision was largely accomplished by modifying the sample's distance from the instrument to improve the data quality. The instrument also includes an ultrafast pulsed laser and improved signal-to-noise ratios to better constrain the timing of events in solar system history. These lasers have a repetition rate of 10 kHz, which will allow the instrument to acquire data times faster than the current engineering design.
The CODEX mass spectrometer, power supplies and timing electronics are already small enough for spaceflight.
Meteorite dating methods
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You can unsubscribe at any time and we'll never share your details to third parties. 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.
What fuctioning meteorite dating methods are certainly right
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.
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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?
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.
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. 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.
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. Jun 29, SwRI is designing the CODEX instrument to use radioisotope dating techniques in situ to determine the age of rocks on other planets or moons. With fiver lasers and a mass spectrometer, the. The commonly accepted billion year age of the earth is derived from radiometric dating of lunar rocks and meteorites in addition to dating methods based on the Gerling-Holmes-Houtermans model.
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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