I understand that carbon dating can be off sometimes but I read that rock strata and tree rings(Bristlecone pine tree rings) are used to create a calibration curve to correct our measurements. How does this work if our oldest tree alive is 6500 years old?
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Rock strata alone can be used to sequence things, not give exact dates. If stratum A overlays stratum B (except in a very folded geology) then A must be younger than B. If B overlays C somewhere else then you have the sequence A-B-C getting older, and so on.
You may also be able to tie that in with some radioisotope dating to fix points in the sequence into a dates. Not carbon for that sort of age, but other radioisotopes with longer half-lives.
Tree ring widths vary with the climate. Good growth one year, poorer the next, maybe a couple of middling ones followed by a good pair. That gives sort of “fingerprint”, in this simple example g,p,m,m g,g that you know the date of. If you find the same fingerprint on an even more ancient piece of timber, you can match that date and count back rings on that piece to when it was young and get fingerprints older than any living tree. You know the age from the rings and you can get the carbon date and build a calibration table.
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