Question

Photosynthetic cyanobacteria caused an increase in atmospheric levels of

A) ozone
B) water
C) oxygen
D) carbon dioxide.

Answer 1

C) oxygen

Step-by-step explanation:

The gaseous product of photosynthesis is oxygen. Cyanobacteria are responsible for much of Earth’s early oxygen.

Answer 2

C...the key is that they are photosynthetic...so they produce oxygen (like plants)!