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Yet few people know how radiometric dating works or bother to ask what assumptions drive the conclusions. This figure wasn’t established by radiometric dating of the earth itself. Radiohalos shouldn’t exist, according to conventional wisdom!
Though they are very tiny, polonium radiohalos have a huge message that cannot be ignored.
For many more examples of the consistancy of dating the same rocks with multiple methods, see Consistent Radiometric Dates by Joe Meert, a Geologist at the University of Florida. Meert's examples not only show that multiple radiometric methods come up with consistent dates for samples from the same locations, but that these results are also consistant with the paleomagnetic signature of the rocks, the position where the rocks would be expected to be (due to continental drift) at the time they were formed, and the cooling curves for the rocks.
(Cooling curves deal with the fact that the different radiometric isotopes become "frozen" in the rocks at different temperatures.
Initial daughter element can often be accounted for by either measuring the amount of an isotope of the daughter element (the ratio of isotopes are almost always constant).
Another possibility is (as in the case of the potassium - argon - K-Ar method) that because the daughter element is gaseous, it would escape from the rock when the rock was molten.
The more I learn about radiometric dating, the more I appreciate the quality of this article.
These are metamorphic rocks and thus have had some of their "history" lost - metamorphosis fully or partially resets the radiometric ages of rocks pointing to younger ages than the true age of the original rock.
Older rocks may have been lost due to erosion or have not yet been discovered.
Sedimentary rocks do not work because they are made up of a mixture of deposits of many other types of rocks, each of which would point to a different age.
At any rate, scientists have devoted a great deal of effort to determining exactly which dating methods are appropriate for which types of rocks.