Thorium lead dating. Geology Chapter 2: Geologic time Flashcards 2019-01-11

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Thorium

thorium lead dating

Let us consider processes that could cause uranium and thorium to be incorporated into minerals with a high melting point. It doesn't say which class lead is in. In the same manner, lead 208 normally theorized as formed only by thorium 232 decay could have been formed by the capture of free neutrons from lead 207. By analogy with the behaviour of Ra, Th and U it can be suggested that Pb, owing to its large mobility, was also fed to the magma by fluids. This produces an isochron yielding the same age as sample A. Dalrymple reports that thirteen samples from the lunar highlands gave the oldest ages. Then a mixing of A and B will have the same fixed concentration of N everywhere, but the amount of D will be proportional to the amount of P.


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Lead dating used

thorium lead dating

The half-lives of uranium 238, 235, and thorium 232 are supposedly known, having been theorized. They are not always the same, so some uncertainties arise in these processes. According to this article the samples were taken from volcanic material that is only 100 million years old. We now have so many things that can make radiometric dating go wrong, and isochrons don't remedy the situation at all, that I think the weight of evidence of radiometric dating is nullified. The lead incorporated within the Earth has been evolving continuously from primordial lead and from the radioactive decay of uranium and thorium isotopes. First, there would be massive contamination problems, as fluids, chemicals, and radioactive substances flowed or were carried from one place to another. I think we can build a strong case for fictitious ages in magmatic rocks as a result of fractional cystallization and geochemical processes.

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Geology Chapter 2: Geologic time Flashcards

thorium lead dating

If rock X has lots of uranium and little daughter product, and rock Y has little uranium and lots of lead daughter product relative to non-radiogenic lead , then one will get a negative slope. Some process is causing the differences in the ratios of these magmatic rocks. It is a compound of zirconium, silicon and oxygen which in its colorless form is used to make brilliant gems. This is a rubidium-strontium isochron for a set of samples of a Precambrian granite body exposed near Sudbury, Ontario. The conclusion is the same, radiometric dating is in trouble.

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IETP

thorium lead dating

Thus geologists assume that the lead in zircons resulted from radioactive decay. Another problem with isochrons is that they can occur by mixing and other processes that result in isochrons yielding meaningless ages. But these same chemical fractionation processes call radiometric dating into question. I count at least three so far -- sorting by density, sorting by melting point, and sorting by how easily something is incorporated into minerals that form at the top of a magma chamber. Although more than one rock type can be generated from a single magma, apparently other mechanisms also exist to generate magmas of quite varied chemical compositions. Any departure from the original relative concentrations of lead-206 and lead-207 relative to lead-204 could then be attributed to radioactive decay.


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Uranium, Thorium, Lead Dating

thorium lead dating

So it is reasonable to expect that initially, the magma is rich in iron, magnesium, and calcium and poor in uranium, thorium, sodium, and potassium. But in actual field conditions, there is no such thing as a closed system. But even if it is true that older radiometric dates are found lower down in the geologic column, which is open to question, this can potentially be explained by processes occurring in magma chambers which cause the lava erupting earlier to appear older than the lava erupting later. Suppose sample B has no P or D but the same concentration of N as A. P2 and P3 are small, since some rocks will have little parent substance. But many minerals take in a lot of uranium.

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Evolution Handbook 3

thorium lead dating

There are those processes taking place when lava solidifies and various minerals crystallize out at different times. Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia. This can also result in isochrons being inherited in the same way. How anyone can keep track of this all is a mystery to me, especially with the difficulties encountered in exploring magma chambers. So we are investing a lot of time and energy to explain how this marvelous agreement of the various methods can arise in a creationist framework. I now give a more natural three-source mixing scenario that can produce an arbitrary isochron, which could not be detected by a mixing test. Note that uranium-238 and uranium-235 give rise to two of the , but rubidium-87 and potassium-40 do not give rise to series.

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Clocks in the Rocks

thorium lead dating

Subduction means that these plates are pushed under the continents by motions of the earth's crust. Thus we can get an isochron by mixing, that has the age of the younger-looking continental crust. Of these, the 14C is unique and used in. The skill of a geochronologist is demonstrated by the ability to attain the knowledge required and the precision necessary with the least number of analyses. How reliable is radiometric dating? It's interesting that isochrons depend on chemical fractionation for their validity. The method deals with both of those difficulties by using the non-radioactive isotope as a comparison standard. I would not want to use a scale that might be right and might be wrong.

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Uranium thorium lead dating method

thorium lead dating

And yet we expect that uranium-lead ratios are determined by radiometeric decay alone or at least sometimes! This chemical fractionation will most likely arise by some minerals incorporating more or less uranium or thorium relative to lead. Several methods for dating ancient materials have been developed. For example, zircons are thought to accept little lead but much uranium. Time is not a direct measurement. In the late 80's the method was refined by mass spectrometry.

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Clocks in the Rocks

thorium lead dating

Lava erupting earlier would come from the top of the magma chamber, and lava erupting later would come from lower down. These three are generally found together in mixtures, and each one decays into several daughter products such as radium before becoming lead. I assume he would have mentioned if any others had been done. Jon Covey cited some references about this, and it will take a lot of work to understand what is going on from a creationist viewpoint. So we have two kinds of processes taking place.

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Geology Chapter 2: Geologic time Flashcards

thorium lead dating

This will cause an apparent large age. Why can't lead isochrons are used to lead-206. They assume that initially the magma was well mixed to assure an even concentration of lead isotopes, but that uranium or thorium were unevenly distributed initially. More Bad News for Radiometric Dating More Bad News for Radiometric Dating Most scientists today believe that life has existed on the earth for billions of years. It is not even necessary for the fractionation to treat parent and daughter equally, as long as it has the same preference for one over the other in all minerals examined; this will also preserve the isochron.

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