Recent lava flows often yield K-Ar ages of about 200,000 years. Also, many of the meteorite dates I saw in the FAQ were apparently simple daughter-to-parent ratio ages. The carbon-14 ends up as a trace component in atmospheric carbon dioxide CO 2. Do different methods agree with each other on the geologic column? And as I said above, I'm also interested to know how much of the fossil-bearing geologic column can be dated by isochrons, and how the dates so obtained compare to others.
Neither date would necessarily be seen as anomalous. This is especially true as the lava is cooling. This type of lava cools quickly, leaving little time for crystals to form, and forms basalt. However, this doesn't remedy the situation and the ages are still too high [low? Where they finally stop to produce lattice distortions and defects there generally occurs discoloring or darkening. This would suffice to give a rock having an average concentration of potassium, a computed potassium-argon age of over 500 million years!
Not knowing if anomalies are always published makes this harder. There is some difficulty in determining the decay constants for the K40-Ar40 system. By 1925, increased confidence in radioisotope dating techniques and the demands of evolution theory for vast amounts of time led to the establishment of an expanded geological time scale.
In addition, Woodmorappe gives over 300 sets of dates "that are in gross conflict with one another and with expected values for their indicated paleontological positions. 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. Maybe it got included from surrounding rock as the lava flowed upward. It's also not uncommon for two methods to agree and for the date to be discarded anyway. Thus these ages, though they generally have a considerable scatter, are not considered as anomalies. By the way, Ar-Ar dating and K-Ar dating are essentially the same method, so between the two of them we obtain a large fraction of the dates being used.
This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. It is interesting that Woodmorappe 1979 gives a number of cases in which standard geological tests are ignored. As these rocks absorb argon, their radiometric ages would increase. Photo Gallery of Dating errors.
My concern is instead to know how much stamina the evidence has against other evidence that may call it into question. Or it could have other explanations. The only correlation I know about that has been studied is between K-Ar and Rb-Sr dating on precambrian rock. The residence time of 36 Cl in the atmosphere is about 1 week. In fact, a couple of the haloes have such low ratios as to imply an age in the thousands of years. This is one reason why just reporting the percentage of anomalies has little meaning.
It could decrease them, if they were regarded as flukes. Your hypothetical example in "More Bad News for Radiometric Dating" is often hard to follow, but it is clearly invalid. But it's not evident how much support this gives to radiometric dating. The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons.
Modern lava flows often come down the sides of volcanoes, and thus become separated from their source by large distances. In general, in one half-life, half of the parent will have decayed. Even some figures from Faure, Principles of Isotope Geology, 1977 are based on another constant that is 2 or 3 percent too low, according to Dalrymple, and so there may be many ages in the literature that need revision by small amounts. Thus we really need some evidence that the different methods agree with each other.
Especially the gaseous radioactive decay byproducts such as argon, radon, and helium are mobile in rock. But if we really understand what is going on, then we should be able to detect discrepant dates as they are being measured, and not just due to their divergence from other dates. These methods can be used to date the age of a sediment layer, as layers deposited on top would prevent the grains from being "bleached" and reset by sunlight.
If you were to measure Ar40 concentration as function of depth, you would no doubt find more of it near the surface than at deeper points because it migrates more easily from deep in the earth than it does from the earth into the atmosphere. Crystals of biotite, for example, and other minerals in igneous or metamorphic rocks commonly enclose minute specks of minerals containing uranium or thorium. It is also being claimed that the different methods have distributions that are similar to one another on a given geologic period. But anyway, I think it is important really to know what patterns appear in the data to try to understand if there is a correlation and what could be causing it. Of 12 dates reported the youngest was 140 million years and the oldest was 2. Annual Review of Nuclear Science.
This is when the dinosaurs are assumed to have become extinct. So these small particles of lava cool very fast. No presently available experimental evidence would exclude the possibility that essentially all the lead-206 in the halo centers was introduced together with the uranium either directly or as parent polonium-210 or lead-210 and thus did not accumulate from uranium. Thus in many cases, the lava or magma will never completely degas, and extra argon will end up trapped in the cooled rock. Annual Review of Nuclear Science. Another factor is that rocks absorb argon from the air.