Why can studies of carbon isotopes be used to detect the presence of past biological activity in rocks?
A) living organisms absorb only the most common carbon isotope
B) living organisms remove all carbon from rocks
C) living organisms absorb certain carbon isotopes more easily than others
D) carbon isotopes are found only in living organisms

Question

Quizplus · Accepted Answer

Living organisms preferentially absorb lighter carbon isotopes, such as carbon-12, over heavier isotopes, such as carbon-13. As a result, the ratio of carbon-13 to carbon-12 in rock samples can be used to infer the presence of past biological activity. If the ratio indicates a higher abundance of carbon-12, it suggests that biological activity was present at the time the rock formed.

Why Can Studies of Carbon Isotopes Be Used to Detect