The ¹³C/¹²C isotopic ratio of geological rocks of different ages has been used to examine whether previous biological activity occurred because compounds of biological origin
A) do NOT contain ¹³C.
B) have a higher proportion of ¹³C that compounds of geological origin.
C) have a lower proportion of ¹³C that compounds of geological origin.
D) are not well preserved in geological samples.

Question

Quizplus · Accepted Answer

Compounds of biological origin have a lower proportion of ¹³C compared to compounds of geological origin. This is because biological processes preferentially incorporate the lighter ¹²C isotope into biomolecules, leading to a lower ¹³C/¹²C ratio in biological samples. Therefore, a lower ¹³C/¹²C ratio in geological samples can be used to infer the presence of previous biological activity.

The ¹³C/¹²C Isotopic Ratio of Geological Rocks of Different Ages