Radiometric dating as practiced is reliable.

Are tape measures viable for measuring length? Tape use assumes the user correctly aligns the end with desired point on the object, the end doesn't slip, the tape doesn't change length, and the person correctly reads the scale. Tape measures can stretch a little and expand and contract with temperature, so the principle of invariant length is clearly false. Separate teams verifying measurements could coordinate. Since these assumptions cannot be guaranteed true at all times, must we denounce the use of tape measures? Obviously not. The reason that length measurements are valid, and radiometric dating is also valid, is that theoretical objections are overcome in practice with reasonable care. Scientists take more than just ordinary care; they worry about every assumption. To be sure, scientists want to avoid mistakes. But if there is a chronic problem with a method, they want to discover it. The small errors due to the early measurement of the half-life of C-14 were discovered. The small errors in C-14 due to changes in the solar flux were detected and corrected. Every time an error is discovered scientists get to advance science, write a paper, and enhance their reputation. If they publish a false result, then some other scientist will discover the error and publish the discrepancy. With this understanding, I now consider Con's specific challenges. How do we know there is no external source of a daughter isotope? For carbon dating, the assumption is that carbon-14 is only entered into the sample by exchange with the atmosphere. The way Libby checked that assumption was to test the methane in natural gas in comparison to methane from sewage. [2. op cit] Natural gas has been underground for a long time so all the carbon-14 should have decayed. The test showed that it had. The methane in sewer gas is from organic sources that should be in equilibrium with the atmospheric ratio, and tests showed that also was true. There are a few cases where exchange is known to be a problem, such as certain biological components of soil. Tests of carbon dating versus known dates determines the circumstances when carbon is not completely isolated. The problem circumstances are then avoided. When the daughter isotope is a gas, as with potassium-argon and argon/argon dating, the gas is purged when the material is molten. The date is then determined from when the material was molten. Scientists use crystals as the sample material to ensure that no gas enters or leaves the sample over time. Intact crystals are selected to ensure there is no intrusion or leakage. Crystals are also used to ensure the integrity of solid isotopes. Zircon crystals are used for uranium-lead dating because zircons naturally contain a lot of uranium and are extremely resistant to damage. As previously explained, the two uranium isotopes always present provide a cross-check on the dating. The two dates must agree. How do we know that cross-checking is not forced to agree? Con implies that scientists systematically throw away data that does not confirm the results they want to get. Scientists are well aware of the potential for that problem, so blind processing [6. http://en.wikipedia.org...] is used systematically. The tests are deliberately made without knowing where the sample came from, so the answer cannot be forced. Libby's original verifications of C-14 dating was done blind, so the carbon dates couldn't be fudged. [2] Labs specialize in different methods of radiometry, so the lab won't know what other methods are being used elsewhere with other samples, let alone what dates are being obtained or are expected. [3] A good example of cross-checking is the dating of the formation of the Hawaiian Islands based upon radiometric dating of lava flows. [7. http://www.soest.hawaii.edu...] The dates showing a straight line of tectonic drift with time references 22 papers published from 1964 to 1987. Dozens of scientists contributed. Are radioactive decay rates constant? Few things in experimental physics have been verified more thoroughly than the invariance of radioactive decay rates. So far, only beryllium, which con correctly cites, has been discovered to have a variation with chemical composition. Baylor University notes summarize, “The possible effects of changing temperature, pressure, chemical state, and electric or magnetic field strength on the three decay mechanisms relevant to geologic dating have been intensively studied, both theoretically and experimentally. These studies have shown that changing environmental conditions have either no measurable effect or a negligible effect (less than 1%, and that only for 7Be, which decays through electron capture) on the rate at which the decay processes occur [9. p. 86-90]. "There is no evidence that decay constants have changed as a function of time during the history of the solar system" (10. p. 41). “ [8. http://www.baylor.edu...] [9. Dalrymple, G.B., 1991, The age of the Earth: Stanford, California, Stanford University Press, 474 p.] [10. Faure, G., 1986, Principles of isotope geology [2nd edition]: New York, John Wiley & Sons, 589 p.] As scientists are better able to measure tiny variations in decay rates, it's not too surprising that small variations due to other causes. A periodic variation of 0.3% in decay rates has been reported and is attributed to solar neutrino flux variations. Con said “the assumption is that the decay rates in different minerals is comparable.” No, the checks, including the ones I cited using different minerals use different elements having different decay rates. Con says that if three samples are taken from the same place, the second two will be “calibrated” to agree with the first. That is incorrect. The samples are not used in any way to calibrate or adjust the process. The radioactive decay rates are measured independently and published for anyone to use. Con's reference [8] has to do with whether the time between particle emissions in radioactive decay are completely random. That has nothing to do with the decay rate. The emissions could be entirely predictable without violating a constant decay rate. It's like counting the number of cars passing a traffic checkpoint each hour. The cars could be equally spaced or randomly spaced without changing the count.. Con's reference [4] is unrelated to our debate. The word radiometry is used to refer to measuring how much infrared energy from the sun is reflected by the surface of the earth. The article discussed the calibration of satellites that measure the reflected energy. Can archaeological artefacts be used to check carbon dating? Con questions if archaeological objects have dates known independently. The ancient Egyptians kept records of the ruling dynasties and the lengths of the periods of the rule of each king, so archaeologists have pieced together a history of ancient Egypt based solely upon the documentary evidence. The earliest dates derived from the records have the greatest uncertainty. The Egyptians typically put wooden boats in the Pharaohs tombs, the wood suitable for carbon dating. When Libby measured the age of the wood, the comparison dates from nearly 5000 years ago were known to within about 200 years, go enough to verify dates within 4%. Since 1950, the Egyptian calendar system has been discovered to rely upon astronomical events that we can determine precisely. This has reduced the uncertainty in the ages as determined independently to about 50 years. Libby also checked samples from European archeology and redwood trees having known dates. An account of all the samples is given with a graph of the dates with error bounds in given in Libby's Nobel acceptance lecture. [11. http://www.nobelprize.org...] Con's objections fail because they are unproved theories avoided by the actual methodologies used.