From the article:
“Dr Condon said that others had approached the debate with a geochemical argument by examining isotopes of carbon while the St Andrews team had looked at the glacial rocks themselves.”
This makes no sense if they mean C-14 (half-life is only 5730 years) for an event in the pre-Cambrian (600 MYBP).
Does he mean relative abundance of C-12 and C-13?
Hmm, maybe — I missed that. C-13 is the decay result of (sez here) boron-13 and nitrogen-13; the abundance of C-13 relative to C-12 (both are stable, ie don’t decay) in a mineral sample could be used to date that sample, or date the period of exposure to weathering.
http://www.astrobio.net/exclusive/293/when-did-life-on-earth-begin-ask-a-rock
“Normally, carbon-13 (C-13, with atomic weight 13), is much rarer than C-12. However, biological processes concentrate C-12, so when organic debris falls to the ocean floor, the C-12 to C-13 ratio rises still further in the sedimentary rock that forms. That ratio is preserved even in rocks that formed billions of years ago.”
however, also see:
http://www.sciencedaily.com/releases/2008/09/080910104202.htm