Aerobic organisms first started building up oxygen in the Earth's atmosphere around
A) 4.6 billion years ago
B) 3.5 billion years ago
C) 4.0 billion years ago
D) 2.4 billion years ago

Question

Quizplus · Accepted Answer

The first signs of oxygen in the Earth's atmosphere date back approximately 2.4 billion years ago, when photosynthetic microorganisms began to evolve and produce oxygen as a byproduct of their metabolic processes. Prior to that, the Earth's atmosphere was mostly composed of carbon dioxide, methane, and nitrogen.

Aerobic Organisms First Started Building Up Oxygen in the Earth's