What evidence would there be if radioactive decay changed 7,000 years ago?

I know we generally operate - or religiously operate - on the principle that fundamental things don't change over time. It's the bedrock of geology - Uniformitarianism. I also believe it is unprovable (which may be bad for my question).

However, assume ¹⁴C was a more unstable isotope 7,000 years ago and decayed with $\lambda$ = 100a. There are other changes in my world as well - but for this question I want to know what our geologic table would look like if the ¹⁴C radioisotope became more stable only 7,000 years ago. In a nutshell I'm trying to hide the true age of the biosphere by making organisms look older, however someone has learned how to detect this.

Oh one more detail - the change was not precipitous. Over 500 years or so the $\lambda$ increased from 100a $\longrightarrow$ 5730a.

Running through a half-life calculator a 7,500 year old sample will ¹⁴C date to 38,900 years old if this change occurred. From comments it appears the overlapping rings from BC 5k~9k will look anomalous.

Other dating methods also exist as noted - DNA mutation rates, magnetic seabed ridges, other radioisotopes - if the evidence left behind by these comparisons could be included in an answers it would help greatly. For example, noncontinuous tree ring calibration curves can be assumed.

My only other thoughts are that maybe some of the $\beta ^-$ particles would be captured in nearby elements showing exotic compounds. E.g., maybe more copper or neon in zinc and sodium deposits. Would we see that or just assume it was normal?

Purpose
This change is "theorized" by only one special scientist, and is a prelude to something worse approaching. The greater scientific community is skeptical because his evidence is "not compelling." I am hoping answers include what evidence such a change would leave behind in the various other disciplines, while also hoping such evidence is "sloppy enough" to discredit my character's theory even though it is true. I need to use your evidence to patch the plot holes, or at least make them sloppy enough that everyone else could realistically miss this.

posted about 5 years ago

Vogon Poet‭

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