There is a systematic difference in utilization of carbon isotopes by photosynthesis, however: carbon-12 is better utilized than the heavier isotopes. So the biosphere is relatively depleted in heavier isotopes. That leaves more heavy isotopes in the environment to participate in non-biological activities.
For this reason, the carbon-13 enrichment of limestone has been taken as a marker of biological activity in the environment in which it was laid down. We see it decrease during the "snowball earth" period, for instance, and increase again afterwards.
Presumably the author is making some reference to this isotopic preference.

Grant Hutchison