How accurate are radiometric dating methods
The ratio of Sr-87 to Sr-86 is graphed versus the ratio of Rb-87 to Sr-86 for several different parts of the rock. Sr-86 is another stable form of strontium, but it isn’t produced by radioactive decay.Thus, it provides an independent analysis of the rock that does not depend on the radioactive decay that is being studied.Sr-86 diffuses more quickly than Sr-87, and that has never been taken into account when isochrons are analyzed. Perhaps, but it’s rather tricky, because the rate of diffusion depends on the specific chemical and physical environment of each individual rock.If the effects of diffusion can be taken into account, it will require an elaborate model that will most certainly require elaborate assumptions. Hayes suggests a couple of other approaches that might work, but its not clear how well. If you believe the earth is very old, then most likely, all of the radioactive dates based on isochrons are probably overestimates. I have no idea, and I don’t think anyone else does, either. Hayes’s model indicates it could add as much as 29 billion years to ages determined with rubidium and strontium, although his model is rather simplistic.
Of course, that error estimate is complete nonsense.
As someone who has studied radioactivity in detail, I have always been a bit amused by the assertion that radioactive dating is a precise way to determine the age of an object.
This false notion is often promoted when radioactive dates are listed with utterly unrealistic error bars.
One way this is done in many radioactive dating techniques is to use an isochron. To understand the problem, let’s start with an example of how radioactive dating works. Sr-87 is not radioactive, so the change is permanent.
The elements rubidium and strontium are found in many rocks. As illustrated above, a neutron in a Rb-87 atom can eject an electron (often called a beta particle), which has a negative charge. We know how long it takes Rb-87 to turn into Sr-87, so in principle, if we analyze the amount of Rb-87 and Sr-87 in a rock, we should be able to tell how long the decay has been occurring.
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If some process brought Sr-87 into the rock, it probably brought different amounts of the atom into different parts of the rock, so the ratio of Sr-87 to Sr-86 won’t stay consistent from one part of the rock to another. He says that there is one process that has been overlooked in all these isochron analyses: diffusion.