Radiometric dating ~ Learning Geology
turbotop.info examines bioscience issues in biodiversity, environment, genomics, biotechnology, Dating in geology may be relative or absolute. Specific examples: When radiometric dating "just works" (or not) the way radiometric dating and stratigraphic principles are used to establish. In a separate article (Radiometric dating), we sketched in some technical detail how these Skeptics of old-earth geology make great hay of these examples.
By comparing the proportions of parent to daughter element in a rock sample, and knowing the half-life, the age can be calculated. Older fossils cannot be dated by carbon methods and require radiometric dating.
Radiometric Dating and the Geological Time Scale
Scientists can use different chemicals for absolute dating: The best-known absolute dating technique is carbon dating, which archaeologists prefer to use. However, the half-life of carbon is only years, so the method cannot be used for materials older than about 70, years.
Subtle differences in the relative proportions of the two isotopes can give good dates for rocks of any age. Scientists can check their accuracy by using different isotopes. The first radiometric dates, generated aboutshowed that the Earth was hundreds of millions, or billions, of years old. Since then, geologists have made many tens of thousands of radiometric age determinations, and they have refined the earlier estimates. Age estimates can be cross-tested by using different isotope pairs.
Results from different techniques, often measured in rival labs, continually confirm each other. Every few years, new geologic time scales are published, providing the latest dates for major time lines.
Older dates may change by a few million years up and down, but younger dates are stable. For example, it has been known since the s that the famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65 million years old. Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date.
It is accurate to within a few thousand years.
Radiometric Dating and the Geological Time Scale
The strict rules of the scientific method ensure the accuracy of fossil dating. Conclusion The fossil record is fundamental to an understanding of evolution.
Fossils document the order of appearance of groups and they tell us about some of the amazing plants and animals that died out long ago. Fossils can also show us how major crises, such as mass extinctions, happened, and how life recovered after them. If the fossils, or the dating of the fossils, could be shown to be inaccurate, all such information would have to be rejected as unsafe.
- Radiometric dating
- Radiometric Dating Does Work!
Geologists and paleontologists are highly self-critical, and they have worried for decades about these issues. Repeated, and tough, regimes of testing have confirmed the broad accuracy of the fossils and their dating, so we can read the history of life from the rocks with confidence.
Educators have permission to reprint articles for classroom use; other users, please contact editor actionbioscience. Currently, he is studying certain basal dinosaurs from the Late Triassic and the quality of different segments of the fossil record.
He holds the Chair in Vertebrate Paleontology at the University of Bristol, UK, in addition to chairing the Masters program in paleobiology at the university. The technique appears to be simple and straightforward, but is actually very difficult and time-consuming. It is not a trivial task! Starting the Radiometric Clocks 1. Living organisms continually exchange carbon with the atmosphere through the process of photosynthesis.
When the organism dies, however, exchange of carbon ceases and the carbon present in the organism becomes isolated. This event death of the organism marks the effective starting of the C 14 clock. One of the most common types of material used in C 14 dating is charcoal e.
These rocks form by the cooling and crystallization of hot silicate liquids magma or lava. As cooling proceeds from high temperatures ca.
A growing mineral may trap small amounts of a radioactive isotope within its crystal structure. When this occurs, the radioactive atoms become effectively isolated or trapped. Subsequent disintegration will produce daughter atoms replacing the original radioactive parents.
In many respects, igneous rocks are the easiest to date because the starting of the clocks are unambiguous. 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.
Radiometric Dating Does Work! | NCSE
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.
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.
Accuracy of Fossils and Dating Methods
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. 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.
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.