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Uranium/Lead Dating Method Almost everyone knows that uranium decays into lead, and that it takes 4.5 billion years for half the uranium to decay. This is its half-life. The ratio of daughter to parent isotopes in a sample might represent an age relationship. If a rock contained no Lead-206 when it first formed, one can assume that the lead either came from the decay of Uranium-238 or water carried it in and deposited it in the rock. If the half-life of the parent is known and the laboratory determines the quantity of parent and daughter isotopes, they can be reliably converted into number of years. As an example, let's suppose we have a sample and find that it has twice as much lead as it does uranium. What are the assumptions we must make about this sample? According to Faure, we must assume the following things to date something using the uranium/lead methods [Faure, pp. 287-288]:
Response: Possibly the results are free of errors, but the assumptions used in radiometric dating always predominate in any test. It seems that "concordia" is not entirely independent of the underlying assumptions used in radiometric dating. What ratio of parent and daughter isotopes were originally present when the rock first formed? How much of each made up the material that became the earth from supernovae occurring long ago? When did those supernovae occur? There may be independent methods, but they all depend on prejudicial assumptions. Is the first assumption valid? How accurately can the initial concentrations of parent and daughter isotopes be known? One's assumptions about the age of the earth are going to affect the assumptions made about the initial concentration of lead. If you believe the earth is very young or recently created, you will assume that most of the lead was there from the creation. If you believe the earth is billions of years old, you will assume that much of the lead wasn't there initially and is the result of uranium decay over billions of years. How old one thinks the earth is will determine which assumption is made about the initial quantity of lead. If one assumes the earth is 10 billion years old, then the assumed amount of initial lead will be less than what one will assume if it is believed the earth is only five billion years old. We cannot assume that initially there was no lead in the earth's crust. First, it is assumed that no element heavier than lithium was formed in the Big Bang. [Silk] Early in 1992, researchers began to doubt this. Theoretically, all the elements up to and including iron can be created during the normal energy producing process of a star, which is called thermonuclear fusion (thermo = heat; nuclear = of an atom's nucleus; fusion = fusing together). It is during this process that nucleosynthesis occurs (when the nucleus of a heavier atom is synthesized by the fusion of two nuclei of lighter atoms). If the universe did begin with a Big Bang, all the elements heavier than iron had to be created in supernova explosions, because the production of heavier elements by fusion does not release energy, as it allegedly does during the fusion process of the lighter elements. Instead, production of heavier elements requires more energy than stars can normally produce. This is why so much energy is released when atoms of uranium are split in nuclear fission: the enormous energy it took to bind that nucleus is freed [Spitzer]. After a star explodes in a supernova, creating uranium and many other elements, the radioactive decay process of uranium to lead could begin. Since evolutionists assume the universe is 13-20 billion years old, much of the initial uranium produced by dying first and second generation stars decayed into radiogenic lead long before the creation of the earth. Most of the radiogenic lead in the earth's crust was generated before the birth of our planet. (If we can detect the neutrino burst from 1987A supernova, we should be able to detect solar neutrinos. However, through decades of neutrino counting, it is clear than not enough neutrinos are being detected to prove that the sun is powered by nuclear fusion. This brings up the question of what really motivated scientists to reject Kelvin’s and Helmholtz’ suggestion that the sun was powered mainly by gravitational contraction--a process which puts an 15-30 million year upper limit on the age of the sun.) Then over an unknown period of time (several million to several billion years--we have no way of knowing), interstellar gas and dust coalesced into the sun and planets as the result of gravitational attraction. Assuming that the universe's age is 15-20 billion years, some of the lead in the earth's crust decayed from uranium long before it became part of the earth. Uranium doesn't care where it is. It will decay in space just as readily in a rock or a star. This long period of interstellar residency would see the extinction of short and medium-lived isotopes, such as polonium since they would decay to lead long before reaching the earth. Joseph Silk and other astronomers think our sun is a third generation star: the product of the Big Bang and two successive periods of star formation and supernovas. This means the uranium decay actually began 10-15 billion years ago, depending how old the universe is and if the universe began by a Big Bang. This uranium decay would result in the production of more lead in the universe than there is uranium. If uranium has a half-life of 4.5 billion years, the universe is two or three U-238 half-lives old, so there should be much more lead than uranium. There are so many unknowns at this point, to make an assumption about the initial lead in the earth's crust simply reveals one's philosophical bias. But now we can ask how much Lead-206 and U-238 are there? The second assumption Faure says we must make is that the sample tested has remained closed to uranium, thorium, lead, and all intermediate daughters throughout its history. There is not even a remote possibility that this is true. Uranium salts are soluble in water containing dissolved oxygen under pressure. These salts migrate readily, both on the surface and underground. The radioactive substances in granite are found mainly on the grain surfaces of the rock crystals. This is in accordance with the principle of fractional crystallization, which is discussed later in the chapter. Some suppose that a diligent and careful statistical analysis of the dates obtained from numerous rock samples will define a mean into which the vast majority of dates will fall. This is naive thinking, as the next section on age inconsistencies shows. How old can we say the moon is when a dozen samples ranging from millions of years to 28 billion years are recorded? Most uniformitarians assume that the fossil record indicates several billion years of geological history.
Potassium-Argon Dating Faure wrote, The conventional K-Ar method of dating depends on the assumption that the sample contained no argon at the time of its formation and that subsequently all radiogenic argon produced within it was quantitatively retained. Because argon may be lost by diffusion even at temperatures well below the melting point, K-Ar dates represent the time elapsed since cooling to temperatures at which diffusion of argon is insignificant [Faure, p. 93].
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Potassium decays to a gas called argon. Faure begins his discussion by saying that it is assumed that the sample submitted for analysis had no radiogenic argon immediately after complete crystallization of the rock, because all argon outgassed prior to solidification. That is only one assumption that is made during the dating process. That assumption is not correct. Each dating scheme has it's own set of assumptions and problems associated with it, but for the sake of brevity, I will concentrate only on the K-Ar method.
In his chapter on K-Ar dating, Faure says the following additional assumptions must be made: 1. No radiogenic Ar-40 produced by decay of K-40 in the mineral during its life time has escaped. Response: Gaseous argon can easily escape wherever microfractures exist in rock. This relates to a very complicated argument Robert Gentry put forth in the scientific literature starting around 1967. Gentry was made a visiting scientist position at the Oak Ridge National Laboratory and given grants by the National Science Foundations. During his tenure there, he made an important discovery that had far reaching ramifications in the creation/evolution debate. A few opponents of Gentry claimed that polonium halos resulted from the removal of uranium daughter products from uranium radiocenters via water flow through microfissures in granitic rocks or by the flow of gaseous radon, a daughter product of uranium decay which decays into polonium. According to them, this is why it appears that the polonium was not associated with uranium radiocenters. Both of these explanations could not convincingly account for the focused halos resulting from discrete point sources of polonium, since these methods of transport would have caused smearing of the halos as some of the polonium atoms decayed in transit. This is because the half-life of Po-218 is only 3.05 minutes, and the half-life of Po-214 is 164 microseconds. The halos result from alpha particle damage to the crystal lattice of the surrounding rock as the polonium decays. It takes approximately 100 million atoms to produce the spherical halos in the biotite crystals surrounding the radiocenters. The brunt of Gentry's hypothesis was that if the earth was molten at some time in its history, how could there be any polonium halos independent of uranium radiocenters? Even if the entire universe had consisted of polonium-218, about six hours later all of it would be Po-210, lead, and helium. The granite could never have been molten, otherwise the Po-218 halos would have been wiped out because it takes far more than six hours for molten granite to cool to a solid. As it turned out concerning Gentry's findings, it was not the criticism by evolutionists that brought about the demise of Gentry's claim that granite was the original creation rock. Rather, creationists, knowing that sedimentary rock generated on day three of the creation week would be void of fossils. If sedimentary rocks containing fossils were found containing granite intrusions from granitic magma, Gentry's claim for granite would be repudiated. This is because fossil-bearing (fossiliferous) sedimentary rocks had to be formed after life was created. I was saddened to see Gentry's hypothesis refuted. Maybe Gentry's hypothesis can be salvaged. Perhaps the fossiliferous sediment has not been intruded by the granite. Instead, what happened is that the Flood water deposits were conformably deposited around denuded granite. One aspect that needs to be thoroughly research is whether the granite is intrusive or overlaid. 2. The mineral became closed to Ar-40 soon after its formation, which means that it must have cooled rapidly after crystallization, unless it formed at a low temperature. 3. No Ar-40 was incorporated into the mineral either at the time of its formation or during a later metamorphic event. 4. An appropriate correction is made for the presence of atmospheric Ar-40. 5. The mineral was closed to potassium throughout its lifetime. 6. The isotopic composition of potassium in the mineral is normal and was not changed by fractionation or other process, except by decay of K-40. 7. The decay constants of K-40 are known accurately and have not been affected by the physical or chemical conditions of the environment in which the potassium has existed since it was incorporated into the Earth. 8. The concentration of Ar-40 and of potassium were determined accurately [Faure, p. 67]. He says that these assumptions require careful evaluation in each case and place certain restrictions on the geological interpretation of K-Ar dates. He says that the last two assumptions are quite general in scope and express certain fundamental conditions of dating by any method based on radioactivity. The isotopic composition of potassium in natural samples is believed to be constant, even though fractionation of potassium isotopes has been observed on a small scale across contacts of igneous intrusion. A correction needs to be on this point. Fractional crystallization can greatly vary the isotopic composition in any igneous formation, even potassium, as Faure says [Faure, p. 68]. For example, Tarbuck and Lutgens mention that feldspar crystals will have calcium-rich interiors surrounded by zones that are progressively richer in sodium, especially if the rate of cooling occurs rapidly enough to prohibit the complete transformation [Tarbuck]. This must be true of rocks of all composition, in accordance with the Bowen's reaction. Denial of this would render the doctrine of fractional crystallization meaningless. Ways argon can be lost from a rock before dating [Faure, p. 69]: 1. Inability of a mineral lattice to retain argon even at low temperature and atmospheric pressure. 2. Either partial or complete melting of rocks followed by crystallization of new minerals from the resulting melt. 3. Metamorphism at elevated temperatures and pressures resulting in complete or partial argon loss depending on the temperature and duration of the event. 4. Increase in temperature due to deep burial or contact metamorphism causing argon loss from most minerals without producing any other physical or chemical changes in the rock. 5. Chemical weathering and alteration by aqueous fluids leading not only to argon loss but also to changes in the potassium content of minerals. 6. Solution and redeposition of water-soluble minerals, such as sylvite. 7. Mechanical breakdown of minerals, radiation damage, and shock waves. Even excessive grinding during preparation of sample for dating by the K-Ar method may cause argon loss. Faure outlines further problems with the K-Ar dating method [Faure, p. 72]. Addition of non-radiogenic argon to sample prior to testing 1. Argon that was dissolved in the magma and that may have originated from the mantle of the Earth or by outgassing of old K-bearing minerals of the crust 2. Argon that was evolved during later thermal metamorphism of the rocks and that diffused into the minerals during that event 3. Atmospheric argon adsorbed on grain boundaries and microfractures while the rock was exposed to the atmosphere in the field and in the laboratory or firmly held within the crystal lattice. There are many other problems associated with the K-Ar dating method, but the above gives one an idea of how great the problems are. Presently, there is far more Ar-40 than the decay of K-40 could have produced in 4.5 billion years. {32} |