Question

question 6 of 10
early organisms turned ______ into oxygen, making life suitable for other organisms.

a. carbon dioxide
b. nitrogen
c. silicon
d. sulfur

Explanation:

Early photosynthetic organisms (like cyanobacteria) used photosynthesis to convert carbon dioxide ($\ce{CO_2}$) into oxygen ($\ce{O_2}$). Nitrogen, silicon, and sulfur are not converted into oxygen by early organisms in this context. So the correct option is A.

Answer:

A. carbon dioxide