Multiple choice

The atmosphere became oxidizing with the appearance of

  1. autotrophic bacteria

  2. cynobacteria

  3. algae

  4. land plants

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Cyanobacteria were the first organisms to perform oxygenic photosynthesis, releasing oxygen as a byproduct. This gradually transformed Earth's reducing atmosphere to an oxidizing one during the Great Oxygenation Event around 2.4 billion years ago.