Uranium lead dating assumptions and constraints

Assumptions of Radioactive Dating • Smilodon's Retreat

DefinitionUranium–Lead dating is the geological age-determination method that U–Pb Decay System and Age CalculationsThe accumulation of Pb in .. of the McClure Mountain syenite: Thermochronological constraints on the age of the. the accuracy of the model assumptions for initial Pb. Deconvolution of these. The numerical ages are all derived from radiometric ages, a topic which you have hopefully been of decades for dating (it is relevant, though, for other uses, as we shall discuss). These assumptions can cause . very solid constraints. PDF | SynonymsU–Pb dating of opal; Uranium–lead ages of opaline tion of constraints for the timing of the basin development,. the rate of.

Also, some materials from prehistoric times, as well as Biblical events, can be dated by carbon The carbon dates have been carefully cross-checked with non-radiometric age indicators. For example growth rings in trees, if counted carefully, are a reliable way to determine the age of a tree. Each growth ring only collects carbon from the air and nutrients during the year it is made.

To calibrate carbon, one can analyze carbon from the center several rings of a tree, and then count the rings inward from the living portion to determine the actual age.

This has been done for the "Methuselah of trees", the bristlecone pine trees, which grow very slowly and live up to 6, years. Scientists have extended this calibration even further. These trees grow in a very dry region near the California-Nevada border. Dead trees in this dry climate take many thousands of years to decay.

Growth ring patterns based on wet and dry years can be correlated between living and long dead trees, extending the continuous ring count back to 11, years ago. An effort is presently underway to bridge the gaps so as to have a reliable, continuous record significantly farther back in time. The study of tree rings and the ages they give is called "dendrochronology".

Tree rings do not provide continuous chronologies beyond 11, years ago because a rather abrupt change in climate took place at that time, which was the end of the last ice age. During the ice age, long-lived trees grew in different areas than they do now. There are many indicators, some to be mentioned below, that show exactly how the climate changed at the end of the last ice age. It is difficult to find continuous tree ring records through this period of rapid climate change.

Dendrochronology will probably eventually find reliable tree records that bridge this time period, but in the meantime, the carbon ages have been calibrated farther back in time by other means.

Calibration of carbon back to almost 50, years ago has been done in several ways. One way is to find yearly layers that are produced over longer periods of time than tree rings.

In some lakes or bays where underwater sedimentation occurs at a relatively rapid rate, the sediments have seasonal patterns, so each year produces a distinct layer. Such sediment layers are called "varves", and are described in more detail below. Varve layers can be counted just like tree rings. If layers contain dead plant material, they can be used to calibrate the carbon ages. Another way to calibrate carbon farther back in time is to find recently-formed carbonate deposits and cross-calibrate the carbon in them with another short-lived radioactive isotope.

Where do we find recently-formed carbonate deposits? If you have ever taken a tour of a cave and seen water dripping from stalactites on the ceiling to stalagmites on the floor of the cave, you have seen carbonate deposits being formed. Since most cave formations have formed relatively recently, formations such as stalactites and stalagmites have been quite useful in cross-calibrating the carbon record. If one predicts a carbon age assuming that the ratio of carbon to carbon in the air has stayed constant, there is a slight error because this ratio has changed slightly.

Figure 9 shows that the carbon fraction in the air has decreased over the last 40, years by about a factor of two. This is attributed to a strengthening of the Earth's magnetic field during this time.

A stronger magnetic field shields the upper atmosphere better from charged cosmic rays, resulting in less carbon production now than in the past. Changes in the Earth's magnetic field are well documented. Complete reversals of the north and south magnetic poles have occurred many times over geologic history. A small amount of data beyond 40, years not shown in Fig. What change does this have on uncalibrated carbon ages? The bottom panel of Figure 9 shows the amount Figure 9. Ratio of atmospheric carbon to carbon, relative to the present-day value top panel.

The bottom panel shows the offset in uncalibrated ages caused by this change in atmospheric composition. Tree-ring data are from Stuiver et al. The offset is generally less than years over the last 10, years, but grows to about 6, years at 40, years before present.

Uncalibrated radiocarbon ages underestimate the actual ages. Note that a factor of two difference in the atmospheric carbon ratio, as shown in the top panel of Figure 9, does not translate to a factor of two offset in the age. Rather, the offset is equal to one half-life, or 5, years for carbon The initial portion of the calibration curve in Figure 9 has been widely available and well accepted for some time, so reported radiocarbon dates for ages up to 11, years generally give the calibrated ages unless otherwise stated.

Radiometric dating - Wikipedia

The calibration curve over the portions extending to 40, years is relatively recent, but should become widely adopted as well. These methods may work on young samples, for example, if there is a relatively high concentration of the parent isotope in the sample. In that case, sufficient daughter isotope amounts are produced in a relatively short time. As an example, an article in Science magazine vol. There are other ways to date some geologically young samples.

Besides the cosmogenic radionuclides discussed above, there is one other class of short-lived radionuclides on Earth. These are ones produced by decay of the long-lived radionuclides given in the upper part of Table 1.

As mentioned in the Uranium-Lead section, uranium does not decay immediately to a stable isotope, but decays through a number of shorter-lived radioisotopes until it ends up as lead. While the uranium-lead system can measure intervals in the millions of years generally without problems from the intermediate isotopes, those intermediate isotopes with the longest half-lives span long enough time intervals for dating events less than several hundred thousand years ago.

Note that these intervals are well under a tenth of a percent of the half-lives of the long-lived parent uranium and thorium isotopes discussed earlier. Two of the most frequently-used of these "uranium-series" systems are uranium and thorium These are listed as the last two entries in Table 1, and are illustrated in Figure A schematic representation of the uranium decay chain, showing the longest-lived nuclides. Half-lives are given in each box.

Solid arrows represent direct decay, while dashed arrows indicate that there are one or more intermediate decays, with the longest intervening half-life given below the arrow. Like carbon, the shorter-lived uranium-series isotopes are constantly being replenished, in this case, by decaying uranium supplied to the Earth during its original creation.

Following the example of carbon, you may guess that one way to use these isotopes for dating is to remove them from their source of replenishment.

This starts the dating clock. In carbon this happens when a living thing like a tree dies and no longer takes in carbonladen CO2. For the shorter-lived uranium-series radionuclides, there needs to be a physical removal from uranium. The chemistry of uranium and thorium are such that they are in fact easily removed from each other.

Uranium tends to stay dissolved in water, but thorium is insoluble in water. So a number of applications of the thorium method are based on this chemical partition between uranium and thorium. Sediments at the bottom of the ocean have very little uranium relative to the thorium.

Radiometric Dating

Because of this, the uranium, and its contribution to the thorium abundance, can in many cases be ignored in sediments. Thorium then behaves similarly to the long-lived parent isotopes we discussed earlier. It acts like a simple parent-daughter system, and it can be used to date sediments. On the other hand, calcium carbonates produced biologically such as in corals, shells, teeth, and bones take in small amounts of uranium, but essentially no thorium because of its much lower concentrations in the water.

This allows the dating of these materials by their lack of thorium. A brand-new coral reef will have essentially no thorium As it ages, some of its uranium decays to thorium While the thorium itself is radioactive, this can be corrected for.

Comparison of uranium ages with ages obtained by counting annual growth bands of corals proves that the technique is page. The method has also been used to date stalactites and stalagmites from caves, already mentioned in connection with long-term calibration of the radiocarbon method.

In fact, tens of thousands of uranium-series dates have been performed on cave formations around the world. Previously, dating of anthropology sites had to rely on dating of geologic layers above and below the artifacts.

But with improvements in this method, it is becoming possible to date the human and animal remains themselves. Work to date shows that dating of tooth enamel can be quite reliable. However, dating of bones can be more problematic, as bones are more susceptible to contamination by the surrounding soils. As with all dating, the agreement of two or more methods is highly recommended for confirmation of a measurement. If the samples are beyond the range of radiocarbon e. Non-Radiometric Dating Methods for the PastYears We will digress briefly from radiometric dating to talk about other dating techniques.

It is important to understand that a very large number of accurate dates covering the pastyears has been obtained from many other methods besides radiometric dating. We have already mentioned dendrochronology tree ring dating above. Dendrochronology is only the tip of the iceberg in terms of non-radiometric dating methods.

Here we will look briefly at some other non-radiometric dating techniques. One of the best ways to measure farther back in time than tree rings is by using the seasonal variations in polar ice from Greenland and Antarctica. There are a number of differences between snow layers made in winter and those made in spring, summer, and fall.

These seasonal layers can be counted just like tree rings. The seasonal differences consist of a visual differences caused by increased bubbles and larger crystal size from summer ice compared to winter ice, b dust layers deposited each summer, c nitric acid concentrations, measured by electrical conductivity of the ice, d chemistry of contaminants in the ice, and e seasonal variations in the relative amounts of heavy hydrogen deuterium and heavy oxygen oxygen in the ice.

These isotope ratios are sensitive to the temperature at the time they fell as snow from the clouds. The heavy isotope is lower in abundance during the colder winter snows than it is in snow falling in spring and summer.

So the yearly layers of ice can be tracked by each of these five different indicators, similar to growth rings on trees. The different types of layers are summarized in Table III. Page 17 Ice cores are obtained by drilling very deep holes in the ice caps on Greenland and Antarctica with specialized drilling rigs.

As the rigs drill down, the drill bits cut around a portion of the ice, capturing a long undisturbed "core" in the process. These cores are carefully brought back to the surface in sections, where they are catalogued, and taken to research laboratories under refrigeration.

A very large amount of work has been done on several deep ice cores up to 9, feet in depth. Enoch, Jubilees, 1, 2, 3 Meqabyan? Will nothing shake your faith? The Fossils date the rocks, and the rocks date the fossils! Bill Huningahke Therein lies the problem … there should be no C14 but there is … SmilodonsRetreat Except that there are known explanations for this: The small apparent non-zero values are less than measurement error.

Thus things like cosmic rays and imperfect vacuums can contribute to the C content even with modern techniques. While that same level of contamination will add some error to the dating of some reasonably aged sample, the error will be small, so long as the sample is not too old.

Alternate source of C14 production. Natural diamonds are not pure carbon. The most common contaminant is nitrogen, 0. Cosmic rays and other sources of radiation can form C14 from N Another possible avenue is C13, which has a small but non-zero neutron absorption cross section. By either mechanism, this is essentially internal contamination. Other methods of dating are more appropriate. Bill Huningahke explained in detail on creation. You believe what you like.

You are meaningless to the scientific community and if you try to promote teaching of your religion in schools, then I will be involved with the groups who stop you. The evidence for evolution and physics working is unbelievably massive and the evidence that creationists lie and misrepresent real science is also massive.

Many of the same principles that are important to things like computers, clocks, and GPS systems are also the same principles that define why radiometric dating works. You accept some, but not all, not because of evidence, but because your beliefs refuse to allow you accept it. You really need to think about a belief system that prevents you from seeing reality for what it is.

Doc Bill Geeze, Creepto-guru, what a load of malarky you can generate. Did you write a word salad program? Well, you did a great job.

Assumption and Constraint Analysis

The paper you referenced is totally useless, as are you, to your argument. The variation was on the order of 1. From your little avatar you look like a happy sort of hobbit. The paper I referenced was useful, as you mentioned, in showing testable and measurable variation in a decay-rate.

That was the point. Do you have scientific experiments that show that all those assumptions hold up for the methods over the period of time that are of interest to you? Or do you pretend that never happens. I suppose ignorance IS bliss … is it? SmilodonsRetreat Fujii, Yasunori et al. The nuclear interaction at Oklo 2 billion years ago.

Nuclear Physics B Constraints on stellar yields and Sne from gamma-ray line observations. New Astronony Reviews Nucleosynthesis in type 1A supernovae. Nucleosynthesis in type II supernovae. Discovery of a supernova explosion at half the age of the universe and its cosmological implications. Calibration against Pliny the Younger. Direct test of the constancy of fundamental nuclear constants.

Oklo interactions have also been used to validate a young earth view after analysis of the restraints imposed on the alpha-decay half-lives. The researchers chose a fluence monitor that is only 1.

What is your field of study? What do you do Kevin?? Are you a disgruntled Science Teacher at a secondary school in Texas raised amidst bible-thumping nitwits who hate gay people and struggle to formulate sentences?? Explain in English how it works in the face of contamination and untrustworthy decay-rates. Let me go through it real slow and maybe the penny will drop.

Let me demonstrate your faulty logic with an anology: We use a stopwatch to calculate the laptime of runners around a race track. The stopwatch can only count long enough to accurately measure runners that run the track faster than 12mph. I tell you that my 92 year old Grandma would like to have her lap timed, she used to be a great runner when she was young, and would love to see how fast she it now. I ask you to do it anyway just to humour her.

Uranium-Lead dating

You cannot now claim that the stopwatch was the wrong way to measure her. The radioactive isotopes created in supernova explosions produce gamma rays with frequencies and fading rates that are predictable according to present decay rates. Therefore, there is has been no measurable change in decay rates overyears and no factors that could affect decay rates have changed in over 1. Your paper by Overman is pretty funny.

Nine references, one of which is a business statistics book and two of which are creationists. But I enjoy watching your confirmation bias. And there is no way to measure the one way speed of light. Try again, loser, with another creationist. How about Kurt Wise?

Or maybe Hugh Ross? Come on, Creepto, get cracking! See how I did that? I suppose the problem comes down to the origin of the granite samples and whether or not they are primordial granite or not. Tell you what though … the diamond Po halos stuff by Snelling is more compelling, as the location of the diamond is not important. I gave the AiG link to Kevin too … I know you love those guys https: Do you only like to argue when your mates are with you? Again, boo fucking hoo. Right, all of chemistry is based on assumptions pulled out of the air because that explains why chemistry works so well.