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Radiometric dating - Wikipedia

How Radiometric Dating Works: Relative not Absolute Ages

See also Counterexamples to an Old Earth. Radiometric dating is a method of determining the age of an artifact by assuming that on average decay rates have been constant see below for the flaws in that assumption and measuring the amount of radioactive decay that has occurred. Because radiometric dating fails to satisfy standards of testability and falsifiability , claims based on radiometric dating may fail to qualify under the Daubert standard for court-admissible scientific evidence. It is more accurate for shorter time periods e. There are a number of implausible assumptions involved in radiometric dating with respect to long time periods. One key assumption is that the initial quantity of the parent element can be determined.

Or, was there some argon trapped in the rocks originally? Recent testing of volcanic material from Mt. Renne et. Renne tested Ar-Ar dating by checking it against the 79 A.

It apparently did. The true age was years. The test was off only 7 years. The conclusions of Renne and his team read as follows:. Of note however is that this test was not double blinded, and the number of such tests is not statistically significant as far as scientific analysis is concerned.

The very fact that these flows cover such great Also, there are several examples where two or three years (k.y.) with a range of between 2cm/k.y. and 50cm/k.y. What is especially interesting is Later, this idea was revised after radiometric dating placed. There are two main types of fossil dating, relative dating and absolute dating. age of a fossil by using radiometric dating to measure the decay of isotopes, Index fossils are fossils that are known to only occur within a very specific age range. such as brachiopods, trilobites, and ammonites work best as index fossils. For this they willfully forget: that by the word of God the heavens were of old There is also a difference in the timescale used to explain the layers. Most radiometric dating techniques must make three assumptions: The age of the fossil can be estimated within the range of the layers above and below it.

Although interesting, it is basically a case study report, and as such it has very little scientific weight as far as statistical predictability. In the first place, I am not primarily concerned with dating meteorites, or Precambrian rocks. What I am more interested in is the fossil-bearing geologic column of Cambrian and later ages.

I will begin this section with a short discussion from Andrew Snelling, an associate professor of geology in El Cajon, California. However, it is well established that volcanic rocks e. In other experiments muscovite was synthesized from a colloidal gel under similar temperatures and Ar pressures, the resultant muscovite retaining up to 0. This is approximately 2, times as much Ar as is found in natural muscovite.

Thus under certain conditions Ar can be incorporated into minerals which are supposed to exclude Ar when they crystallize. In summary, many scientists assume that since argon is a gas, all of it should have escaped from the lava before it cooled.

Therefore, all the 40 Ar in the rock should be the result of decay from potassium. Based on the measured potassium, argon, and the decay rate, they calculate an age. That is why it does not matter how long the magma was in the volcano before it erupted. They believe that when the volcano erupts, all the 40 Ar escapes, and the atomic clock gets reset to zero. If all the argon escaped from hot lava of volcanoes that erupted long ago, then all the argon should escape from the hot lava of volcanoes that erupt in modern times too.

But modern lava does have 40 Ar in it. However, how are these calibration methods established? Upon what basis are they validated? Let me emphasize again that this dating method is a relative dating method. In other words, it must be calibrated relative to a different dating method before it can be used to date materials relative to that other dating method.

This same problem exists for all other relative radiometric dating techniques. Fission track dating is a radioisotopic dating method that depends on the tendency of uranium Uranium to undergo spontaneous fission as well as the usual decay process.

The large amount of energy released in the fission process ejects the two nuclear fragments into the surrounding material, causing damage paths called fission tracks. These tracks can be made visible under light microscopy by etching with an acid solution so they can then be counted. The usefulness of this as a dating technique stems from the tendency of some materials to lose their fission-track records when heated, thus producing samples that contain fission-tracks produced since they last cooled down.

The useful age range of this technique is thought to range from years to million years before present BPalthough error estimates are difficult to assess and rarely given. Generally it is thought to be most useful for dating in the window between 30, andyears BP. A problem with fission-track dating is that the rates of spontaneous fission are very slow, requiring the presence of a significant amount of uranium in a sample to produce useful numbers of tracks over time. Additionally, variations in uranium content within a sample can lead to large variations in fission track counts in different sections of the same sample.

The principle involved is no different from that used in many methods of analytical chemistry, where comparison to a standard eliminates some of the more poorly controlled variables. In the zeta method, the dose, cross section, and spontaneous fission decay constant, and uranium isotope ratio are combined into a single constant. Of course, this means that the fission track dating method is not an independent method of radiometric dating, but is dependent upon the reliability of other dating methods.

The reason for this is also at least partly due to the fact that the actual rate of fission track production. Some experts suggest using a rate constant of 6. Wagner, Letters to NatureJune 16, For example, all fission reactions produce neutrons. What happens if fission from some other radioactive element, like U or some other radioisotope, produces tracks?

Might not these trackways be easily confused with those created by fission of U ? The human element is also important here. Fission trackways have to be manually counted. Geologists themselves recognize the problem of mistaking non-trackway imperfections as fission tracks. For example, it is recommended that one choose samples with as few vesicles and microlites as possible. But, how is one to do this if they are so easily confused with true trackways?

True tracks are straight, never curved. True tracks are thought to form randomly and have a random orientation. Certain color and size patterns within a certain range are also used as helpful hints.

This is yet another reason why calibration with other dating techniques is used in fission track dating. And, it gets even worse. The tracks through fluid are also interesting. This is because a fission fragment traveling through a fluid inclusion does so without appreciable energy loss. These problems have resulted in several interesting contradictions, despite calibration. In addition, published data concerning the length of fission tracks and the annealing of minerals imply that the basic assumptions used in an alternative procedure, the length reduction-correction method, are also invalid for many crystal types and must be approached with caution unless individually justified for a particular mineral.

Tektites are thought to be produced when a meteor impacts the Earth. When the massive impact creates a lot of heat, which melts the rocks of the Earth and send them hurtling through the atmosphere at incredible speed. As these fragments travel through the atmosphere, they become superheated and malleable as they melt to a read-hot glow, and are formed and shaped as they fly along.

It is thought that the date of the impact can be dated by using various radiometric dating methods to date the tektites. For example, Australian tektites known as australites show K-Ar and fission track ages clustering aroundyears.

The problem is that their stratigraphic ages show a far different picture. Edmund Gill, of the National Museum of Victoria, Melbourne, while working the Port Campbell area of western Victoria uncovered 14 australite samples in situ above the hardpan soil zone.

This zone had been previously dated by the radiocarbon method at seven locales, the oldest dating at only 7, radiocarbon years Gill Charcoal from the same level as that containing specimen 9 yielded a radiocarbon age of 5, years.

The possibility of transport from an older source area was investigated and ruled out. Aboriginal implements have been discovered in association with the australites. A fission-track age ofyears and a K-Ar age ofyears for these same australites unavoidably clashes with the obvious stratigraphic and archaeological interpretation of just a few thousand years. This is problematic. Here we have the K-Ar and fission track dating methods agreeing with each other, but disagreeing dramatically with the radiocarbon and historical dating methods.

These findings suggest that, at least as far as tektites are concerned, the complete loss of 40 Ar and therefore the resetting of the radiometric clock may not be valid Clark et al. It has also been shown that different parts of the same tektite have significantly different K-Ar ages McDougall and Lovering, This finding suggests a real disconnect when it comes to the reliability of at least two of the most commonly used radiometric dating techniques.

In short, it seems like fission track dating is tenuous a best even when given every benefit of the doubt. It is just too subjective and too open to pitfalls in interpretation to be used as any sort of independent measure of estimating elapsed time. There is a methodological problem connected with the manner in which geologists infer the argon-retention abilities of different minerals. Concerning the suitability of different minerals for K-Ar dating, Faurep.

By comparing the K-Ar dates yielded by such minerals with the expected ones. Thus the correctness of the geologic time scale is assumed in deciding which minerals are suitable for dating.

For example, concerning the use of glauconies for K-Ar dating, Faurep. It is also interesting that Faurepp. Thus fission track dating is not an independent test that helps to verify the accuracy of other tests. The result is that radiometric dating in general is in danger of being based on circular reasoning. In Dr.

Raul Esperante teamed up with Dr. This formation is approximately meters thick and consists of many layers of sedimentary rock. Yet, within essentially all of these layers are hundreds of very well preserved fossil whales. In fact, many of them are so well preserved that their baleen is still intact and attached in the usual position that baleen is attached in living whales. Usually baleen detaches within a few days or even hours after death. Some of the fossilized whales and dolphins also have preserved remains of skin outlines around the fossilized bones.

The skeletons themselves are generally well articulated and show no evidence of scavenging or significant decay. Cosmogenic nuclides are isotopes that are produced by interaction of cosmic rays with the nucleus of the atom. The various isotopes produced have different half lives see table. Cosmogenic dating using these isotopes are becoming a popular way to date the time of surface exposure of rocks and minerals to cosmic radiation.

While the idea is fairly straightforward, there are just a few problems with this dating method. To illustrate this problem, consider that 3 H dating has been used to establish the theory that the driest desert on Earth, Coastal Range of the Atacama desert in northern Chile which is 20 time drier than Death Valley has been without any rain or significant moisture of any kind for around 25 million years.

The only problem with this theory is that recently investigators have discovered fairly extensive deposits of very well preserved animal droppings associated with grasses as well as human-produced artifacts like arrowheads and the like.

Radiocarbon dating of these finding indicate very active life in at least semiarid conditions within the past 11, years a far cry from 25 million years. So, what happened? As it turns out, cosmogenic isotope dating has a host of problems.

How can the absolute age of rock be determined What is the best radiometric dating What are two radiometric dating methods determining a Time range that they useful for dating if half life is too short compared with age oft 2little parent. Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes. Learn about half-life and how it is . Radiometric dating is a method of determining the age of an artifact by For example, in uranium-lead dating, they use rocks containing The effect of this on alpha decay, which is the most common decay mode in radiometric dating, This can happen due to one of three forces or "interactions": strong.

The production rate is a huge issue. So many variables become somewhat problematic. This problem has been highlighted by certain studies that have evaluated the published production rates of certain isotopes which have been published by different groups of scientists.

The Himalayan mountains are said by most modern scientists to have started their uplift or orogeny some 50 million years ago. However, recently in Yang Wang et.

How Radiometric Dating Works: Relative not Absolute Ages

The new evidence calls into question the validity of methods commonly used by scientists to reconstruct the past elevations of the region:. The following is the data from these tests: 5. If the present data are representative, argon of slightly anomalous composition can be expected in approximately one out of three volcanic rocks.

Radiometric dating

Dalrymple may have a point. It seems like rocks dating within one or two million years cannot be accurately dated by K-Ar techniques just because of the relatively wide ranges of error. However, can rocks that are tens or hundreds of millions of years be more accurately dated? Perhaps, if these rocks were in fact closed systems and were not subject to contamination by external argon.

Investigators also have found that excess 40 Ar is trapped in the minerals within lava flows. The obvious conclusion most investigators have reached is that the excess 40 Ar had to be present in the molten lavas when extruded, which then did not completely degas as they cooled, the excess 40 Ar becoming trapped in constituent minerals and the rock fabrics themselves.

However, from whence comes the excess 40 Ar, that is, 40 Ar which cannot be attributed to atmospheric argon or in situ radioactive decay of 40 K? Many recent studies confirm the mantle source of excess 40 Ar.

Hawaiian volcanism is typically cited as resulting from a mantle plume, most investigators now conceding that excess 40 Ar in the lavas, including those from the active Loihi and Kilauea volcanoes, is indicative of the mantle source area from which the magmas came.

Considerable excess 40 Ar measured in ultramafic mantle xenoliths from Kerguelen Archipelago in the southern Indian Ocean likewise is regarded as the mantle source signature of hotspot volcanism. Further confirmation comes from diamonds, which form in the mantle and are carried by explosive volcanism into the upper crust and to the surface. When Zashu et al. The conventional K-Ar dating method was applied to the dacite flow from the new lava dome at Mount St.

Helens, Washington.

Three methods of radiometric dating and explain the age range for which they are most effective

These dates are, of course, preposterous. The fundamental dating assumption no radiogenic argon was present when the rock formed is brought into question. Instead, data from the Mount St. Phenocrysts of orthopyroxene, hornblende and plagioclase are interpreted to have occluded argon within their mineral structures deep in the magma chamber and to have retained this argon after emplacement and solidification of the dacite. Orthopyroxene retains the most argon, followed by hornblende, and finally, plagioclase.

The lava dome at Mount St. Helens dates very much older than its true age because phenocryst minerals inherit argon from the magma. The study of this Mount St. Potassium is about 2. Argon is about 3.

We can assume then that the magma is probably about 2. Now, Lets say we are trying to date a one billion year old rock. How much of it would be 40 K? Starting with 0. This would leave us with a 0. This gives about 0. This is about one ten millionth of the mass of the rock, a very tiny fraction. If the rock weighed one gram, the Ar in the rock would weight one ten millionth of a gram. And yet, with a relatively large amount of argon in the air, argon filtering up from rocks below, excess argon in lava, the fact that argon and potassium are water soluble, and the fact that argon is mobile in rock and is a gas, we are still expecting this wisp of argon gas to tell us how old the rock is?

The percentage of 40 Ar is even less for younger rocks. For example, it would be about one part in million for rocks in the vicinity of million years old. However, to get just one part in 10 million of argon in a rock in a thousand years, we would only need to get one part in 10 billion entering the rock each year. This would be less than one part in a trillion entering the rock each day, on the average. This would suffice to give a rock an average computed potassium-argon age of over a billion years.

Some geochronologists believe that a possible cause of excess argon is that argon diffuses into certain minerals progressively with time and pressure. Significant quantities of argon may be introduced into a mineral even at pressures as low as one bar.

We can also consider the average abundance of argon in the crust. This implies a radiometric age of over 4 billion years.

So a rock can get a very old radiometric age just by having average amounts of potassium and argon. It seems reasonable to me that the large radiometric ages are simply a consequence of mixing, and not related to ages at all, at least not necessarily the ages of the rocks themselves. The one better than radiometric dating? How reliable are radiometric dating methods for deciding the age of the Earth? More questions. Why don't creationists trust radiometric dating methods? Why do some creationists think the only dating method scientists have at their disposal is radiometric dating?

Answer Questions How do layers on sandstone stay together in a rock form? Why scientist finds the particulate theory useful? Why are these geology answers so old and wrong? Most common insects in northern coastal Alaska roughly between Point Lay and Shishmaref, give or take miles?

The reason why this is the case is that radiometric dating is based on Best for ages in the ranges of hundreds to thousands of years, with an. Answer to List three methods of radiometric dating, and explain the age range for which they are most effective. In most cases, we cannot use isotopic techniques to directly date fossils or the sedimentary rocks they are found in, but we can constrain their ages by dating igneous One good example is granite, which normally has some potassium feldspar Radiocarbon dating can be used on sediments or sedimentary rocks that.

I found a Mars Meteorite 70 Grams Why does the new year start half way through the winter? Did they really find a Fresh Water ocean under the Atlantic Ocean? What Fossils are these? The sample must be analyzed using a very sensitive mass-spectrometer, which can detect the differences between the masses of atoms, and can therefore distinguish between 40 K and the much more abundant 39 K.

Biotite and hornblende are also commonly used for K-Ar dating. An important assumption that we have to be able to make when using isotopic dating is that when the rock formed none of the daughter isotope was present e. A clastic sedimentary rock is made up of older rock and mineral fragments, and when the rock forms it is almost certain that all of the fragments already have daughter isotopes in them.

Furthermore, in almost all cases, the fragments have come from a range of source rocks that all formed at different times. If we dated a number of individual grains in the sedimentary rock, we would likely get a range of different dates, all older than the age of the rock. It might be possible to date some chemical sedimentary rocks isotopically, but there are no useful isotopes that can be used on old chemical sedimentary rocks.

Radiocarbon dating can be used on sediments or sedimentary rocks that contain carbon, but it cannot be used on materials older than about 60 ka. Assume that a feldspar crystal from the granite shown in Figure 8. The proportion of 40 K remaining is 0. Using the decay curve shown on this graph, estimate the age of the rock.

An example is provided in blue for a 40 K proportion of 0.

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  1. I well understand it. I can help with the question decision. Together we can find the decision.

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