The ¹³C/¹²C isotopic ratio of geological rocks of different ages has been used as evidence for or against past biological activity,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 use the lighter ¹²C isotope, leading to a lower ¹³C/¹²C ratio in biological material. Therefore, rocks with a lower ¹³C/¹²C ratio are thought to be associated with past biological activity.

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