He may suggest that the rock contained crystals called xenocrysts that formed long before the rock solidified and that these crystals gave an older date. It is true that by using additional isotopes if they are sufficiently abundant and do not fractionate , one can often detect mixings of multiple sources. Geochronologists use the branching ratio as a semi-emperical, adjustable constant which they manipulate instead of using an accurate half-life for K40. For isochrons, which we will discuss later, the conditions are different. Rybka claims that experimental evidence suggests that decay rates have changed over time: Two cases where it appears that the half life is increasing with time are as follows.
Data produced by the Petroleum Institute at Victoria, New Zealand, showed that petroleum deposits were formed 6,000-7,000 years ago. The sections on the branching ratio and dating meteorites need updating. So argon is being produced throughout the earth's crust, and in the magma, all the time. If a lava flow lies above geologic period A and below B, then allowable ages are anything at least as large as A and no larger than B. Not infrequently such resetting of the radiometric clocks is assumed in order to explain disagreements between different measurements of rock ages. This will make it more difficult to detect this added argon by the spectrum test described below. Of course, this would lead to a major, worldwide catastrophe.
We now consider whether they can explain the observed dates. Excess argon could even cause different minerals in a given formation to yield similar K-Ar ages, since they all might have similar concentrations of K, approximately equal to its abundance in the earth's crust, and similar concentrations of argon 40, due to the partial pressure of argon 40 being similar during cooling. A ratio of infinity that is, all daughter and no parent means an age of essentially infinity. But it was not until the late 1950s that all the pieces were in place; by then the phenomenon of radioactivity was understood, most of the naturally occurring isotopes had been identified and their abundance determined, instrumentation of the necessary sensitivity had been developed, isotopic tracers were available in the required quantities and purity, and the half-lives of the long-lived radioactive isotopes were reasonably well known. This paper also discusses Mount St. This is regrettable, because I believe he was a careful and sincere scientist.
The answer is that these methods, are far from infallible and are based on three arbitrary assumptions a constant rate of decay, an isolated system in which no parent or daughter element can be added or lost, and a known amount of the daughter element present initially. What about rocks that are thought not to have their clock reset, or to have undergone later heating episodes? I would like to know what is the exact or approximate information content of this assertion, and whether it could be or has been tested statistically. Consider this: if a specimen is older than 50,000 years, it has been calculated that it would have such a small amount of C14 that for practical purposes it would show an infinite radiocarbon age. Slusher , and Rybka also claim that the evidence from pleochroic halos indicates that decay rates have not been constant over time: … evolutionist geologists have long ignored the evidence of variability in the radii of pleochroic halos, which shows that the decay rates are not constant and would, thus, deny that some radioactive elements such as uranium could be clocks. He may suggest that some other very old material had contaminated the lava as it passed through the earth. So a rock can get a very old radiometric age just by having average amounts of potassium and argon.
The final example listed in is a supposed 34 billion-year Rb-Sr isochron age on diabase of the Pahrump Group from Panamint Valley, California, and is referenced to a book by Faure and Powell. This shows we should not trust radiometric dating. When trying to find the best solution to a problem like this, there are generally a huge number of possible solutions. This is true for Rb-Sr, Pb-Pb, Sm-Nd, Lu-Hf, and Re-Os dating methods, as well as the Ar-Ar spectrum method. Also, since some rocks hold the Ar40 stronger than others, some rocks will have a large apparent age, others smaller ages, though they may actually be the same age. So if a rock has tiny cracks permitting gas to enter or escape or permitting the flow of water, the radiometric ages could be changed substantially even without the rock ever melting or mixing. It's interesting to note that in a few cases, old radiometric dates are above young ones.
. This is called the biostratigraphic limit of the flow. They noted, 'The solubility of Ar in the minerals is surprisingly high'. We will also get a distribution of averaged values for samples in each period. A system that is not closed is an open system. I showed that the fact that the great majority of dates come from one method K-Ar and the fact that many igneous bodies have very wide biostratigraphic limits, where many dates are acceptable, makes the percentage of anomalies irrelevant to the question I am asking. Devonian corals, for example, show nearly 400 days per year.
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 radii of these rings are proportional to the energies of the particles. Leaching also occurs, releasing argon from rocks. Geologists often say that ages that are too old are due to excess argon. This is an evidence that these varves were laid down rapidly. The original data are from a report by Wasserburg and others , who plotted the data as shown but did not draw a 34-billion-year isochron on the diagram.
Each of the 8 a-particles emitted during the disintegration of U238 to Pb206 produces a dark ring in biotite. For example, one isochron yielded a date of 10 billion years. Potassium is found to be very mobile under leaching conditions. This will make the sample appear artificially old right away. Or the lava might have cooled quickly, due to rainfall. We can also consider that most volcanoes and earthquakes occur at boundaries between plates, so if the lava has flowed before, it is likely to flow again nearby, gradually increasing the age.
Let's suppose that we have geologic periods G1. This rather damaging result was explained away saying that enough evidence of correct radii for defferent geologic periods and sufficient variation in the same period have been obtained that one is forced to look for a different explanation of such variations as were observed by Joly. This will retain the isochron property, but will make the isochron look too old. A number of recent lava flows within the past few hundred years yield potassium-argon ages in the hundreds of thousands of years range. You have to follow arguments between experts on different issues and see where they go. Rocks in areas having a complex geological history have many large discordances. The results are only accepted if they agree with what is already believed.
Dickin Radiogenic Isotope Geology, 1995, p. The carbon-14 age of the buried trees is only 225 years, but some of the overlying volcanic material has a 465,000-year potassium-argon age. Many historical volcanoes give K-Ar dates that are much too old, even if the reasons for this are understood. But argon 40 coming up from the mantle and diffusing into a mineral would not be detectable in this way, because it has a higher ratio of argon 40 to argon 36. This is formed when lava is sticky and bubbles of gas in it explode.