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Decay changes matter, in that one element decays into another as it emits radiation.The rate of decay is different from teh decay itself. Decay rates do not change. Ever. Period. There's a reason we use the term "constant."Decay rates are a function of the half-life of a given element. Over the course of the half life, 50% of any given sample will decay. That half-life does not change.No. Just as decay rates are not affected by modern floods. You can take a bit of Uranium, keep it in a dry desert, submerged in the ocean, or in the vaccuum of space and it will still decay at exactly the same rate in each circumstance. So too with every other form of radioactive decay.The amount of the radioactive substance is irrelevant. You could have 100 parts per million of C14, 1000 ppm, 1 ppm, or 100,000 ppm, and the half-life of C14 would not change at all.You can take 100kg of Uranium or 100g of Uranium; after the half-life has passed (a few million years in the case of Uranium, as I recall), 50% of each sample will have decayed.Yes, the amount of "decayed Uranium" changes based on how much Uranium is in the sample; but that's why we measure the rate of decay with half-lives, because that is the constant independent of all other variables. And the half-life is what we use to date samples. Radioactive decay works at the same constant rate regardless of environmental conditions. Uranium in the Earth's molten mantle decays with the same half-life as Uranium in the vacuum of space. A flood will not change radioactive decay rates at all.

I'm not sure what you mean, Buz. If you're referring to the decay itself, then yes - the radioactive isotopes decay into their products (some of which are themselves radioisotopes and decay into their own products at their own half-life rate). If you start with a sample of Uranium-238 (the msot common isotope of Uranium), you'll eventually wind up with lead (though there are 18 intermediate elements in the decay chain, so it would take quite a while given Uranium's 4+ million year half-life).Radiation does affect surrounding matter in different ways, as well. We use some radioactive decay to generate heat for space probe batteries, for instance (the Voyager probes generate electricity from the heat of radioactive decay, as their mission sends them too far from the Sun to use solar power). Radiation can be in the form of an emitted neutron, an alpha particle, etc. Alpha radiation won't pass through a sheet of paper or human skin; gamma radiation won't be stopped by less than a concrete wall or preferably lead.But I'm not sure what effect you're talking about that may have relevance to dating. The only thing I can think of is the actual decay itself, where the C14 (or other radioisotope) is transmuted into anotehr element (Nitrogen in the case of C14) by the decay itself. That change is exactly what makes radioisotope dating possible, of course. If you have a sample, and you find a proportion of 50% C14 and 50%N14 (the specific isotope that C14 decays into), then you know that one half-life has passed within a margin of error (which amounts to about 5700 years). You're on to something Buz - atmospheric amounts of C14 do have a role in C14 dating. That's why we need to calibrate our dating methodologies. This is done in several ways - by measuring C14 quantities in ice cores, by matching C14 dating to independent, separate isotopes, by using geologic evidence like annual sedimentary layers, etc.C14 dating is far more involved than just taking a sample, measuring the amount of C14, and coming up with a date. That's the basic mechanic, but as ever in science, we like to independently verify results so that we know with reasonable certainty that we're being accurate.Remember, there are many ways to date samples, especially "dirt." When we try to get an accurate date for a sample, we try to find methodologies that independently arrive at similar results to verify accuracy. That way, if one of them is vastly different from the others, we know something's up.In the case of the Flood, C14 isn't going to be wildly affected by suddenly inundating the Earth in water for a year. Modern floods don;t change the rate of decay. C14 isn't produced by life (it's just trapped in organic compounds because it's Carbon - it actually originates as CO2 in the atmosphere, where the Sun's rays cause the isotope C14 to form The CO2 containing C14 is then inhaled by plants, and later consumed by things that eat the plants, etc), so killing everything alive won't have an effect.You can increase atmospheric C14 with massive wildfires (releasing the trapped carbon back into the atmosphere). You could decrease it by blocking out the Sun, meaning no new C14 is made and existing C14 continues to decay. But the proportion of C14 to its decay products would remain the same in either case, and the rate of decay would remain constant, letting us still date samples accurately (once we calibrate our testing for known atmospheric levels of C14, by using samples containing C14 that have also been dated using other methods - we can use ice cores for that, etc).In all of these cases, C14 dating remains accurate.C14 dating becomes inaccurate when date something too old. After around 50-60,000 years, any given sample will have completely decayed. The closest analogy would be that C14 dating is a ruler; you can accurately measure things less than a foot long, but longer than that and you'll need a yard stick.