However, I also understand that there is very little radiometric evidence on earth of a 4+ billion year formation. It is also the case that material on earth arrived from outside of the solar system and thus at least conceivable might predate the formation of the earth by a large margin. No changes in decay rates would be required.
I understand better now (or should have read more carefully before). You are correct that we haven't found anything on the planet that is original, unaltered material from it's initial formation.
However, everything we have that is clearly younger than the earth points back to an origin of 4+ billion years. In addition there is good reason to expect the moon to be close to the same age as the earth but possibly younger and it dates to the same time.
In addition, because of the nature of the materials in the meteorites, there is good reason to expect them or at least most of them to originate at the time of the formation of the solar system too and they date in the 4+ billion year time as well.
You are right that there is some mixing in of the idea of how the solar system formed mixed into the thinking here but if that is ignored that there is still have another form of consillience to explain-- that of the agreement of measurements made of the different samples -- earth based material, meteorites and the moon samples.
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