Multiple choice

Which of the following was absent in the atmosphere of the primitive earth?

  1. oxygen

  2. carbon dioxide

  3. nitrogen

  4. ammonia

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

The primitive Earth's atmosphere (approximately 4.6-2.5 billion years ago) was largely devoid of free oxygen. Oxygen only accumulated significantly after photosynthetic organisms (cyanobacteria) evolved and began producing it through photosynthesis.