J.William Schopf discovered a fossil cyanobacterium in Australian rocks that are 3.5 billion years old.The specific ratio of carbon isotopes (¹³C:¹²C) in the fossil indicated that the organism A) produced atmospheric oxygen through photosynthesis. B) produced atmospheric carbon dioxide through photosynthesis. C) used atmospheric carbon dioxide in photosynthesis. D) consumed carbohydrates for energy. E) had an extraterrestrial origin.

Question

Quizplus · Accepted Answer

The specific ratio of carbon isotopes in the fossil indicates that the organism used atmospheric carbon dioxide in photosynthesis. This is because photosynthetic organisms preferentially use the lighter carbon isotope (^12C) over the heavier one (^13C), leading to a distinctive carbon isotope signature in organisms that photosynthesize.

JWilliam Schopf Discovered a Fossil Cyanobacterium in Australian Rocks That