Multiple choice

Which of the following appeared on the earth with the evolution of the plants but was absent in the past?

  1. CO2

  2. Methane

  3. Ammonia

  4. Oxygen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Oxygen was largely absent in Earth's early atmosphere. With the evolution of photosynthetic plants (and earlier cyanobacteria), oxygen began accumulating as a byproduct of photosynthesis. This 'Great Oxygenation Event' dramatically changed Earth's atmosphere. Option D correctly identifies oxygen as the new gas.

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