Approximately two billion years ago, ________ were primarily responsible for initially oxygenating Earth.
A) algae
B) Archaea
C) cyanobacteria
D) purple sulfur bacteria

Question

Quizplus · Accepted Answer

Cyanobacteria were the first organisms to carry out photosynthesis and release oxygen into the atmosphere, which began approximately two billion years ago. The other options listed did not play a significant role in oxygenating Earth at this time.

Approximately Two Billion Years Ago, ________ Were Primarily Responsible for Initially