It is interesting that contamination and fractionation issues are frankly acknowledged by the geologic community. If there is significant convection in the magma, this would be minimized, however. Metamorphism or alteration. Indeed, special creationists have for many years held that where science and their religion conflict, it is a matter of science having to catch up with scripture, not the other way around. The CRA conventions include a usage of the Libby half-life, b usage of Oxalic Acid I or II or any appropriate secondary standard as the modern radiocarbon standard, c correction for sample isotopic fractionation to a normalized or base value of
With so many unknowns I don't think so. Thorium is close to uranium in the periodic table, so it may have similar properties, and similar remarks may apply to it. To date older fossils, other methods are used, such as potassium-argon or argon-argon dating.