To me the most interesting element in debates of this sort is not helium or argon, but technetium.
Now, technetium (Tc) is a most interesting element in that:
a) All of its isotopes are radioactive.
b) It's not the end product of typical nuclear decay of any naturally occurring heavier elements (other than rare cases of spontaneous fission of uranium).
c) It is not found in the Earth's crust except in minute amounts (nanograms per kilogram of uranium).
But the decay products of its longest lived isotopes, which are both stable, are found in the Earth's crust ( Tc-97, half life 2.6 million years, decays to Molybdenum-97; Tc-98, half life 4.2 million years, decays to Ruthenium-98 ) in much larger abundances than that.
d) Tc has been found in stars via spectroscopy, and in fact, this is a data point supporting the current theories of nucleosynthesis in stars.
e) Like all elements, it can be produced artificially by nuclear reactions; in fact this is how it was discovered.
If the YE hypothesis were valid, why don't we observe Technetium in the Earth's crust in abundances comparable to its decay products Ruthenium and Molybdenum and in association with them ? There is nothing strange about Tc chemically, it's a typical transition metal.
I think it's very telling that entering "technetium" in the search engines of YEC websites produces...nothing.
I don't think Technetium is favorable to their case.
It would be nice to see a YEC try to explain this. At least they'd have to be original; no boilerplate from their favorite sites to rely on.
And if Tc is too exotic, there are other short-lived isotopes that are not part of other element's decay series, that aren't found on Earth, like Lead-205.
Why no Lead -205 (half life 15 million years), but lots of stable Lead isotopes ?
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