Question

Which of the following gases is relatively abundant today but was much less common or absent in the early atmosphere of Earth?

Options:
Option 1: Nitrogen
Option 2: Oxygen
Option 3: Carbon dioxide
Option 4: Methane

Answer 1

Oxygen was much less common in Earth's early atmosphere but increased in abundance due to photosynthesis by blue-green algae and later plants. Option 2.

Step-by-step explanation:

The gas that was much less common or absent in the early atmosphere of Earth but is relatively abundant today is oxygen. Unlike nitrogen, which has been abundant due to its geochemical inertness, oxygen is almost entirely of biological origin and was not a significant part of Earth's early atmosphere.

The early atmosphere, in a more chemically reduced state, likely contained hydrogen-containing gases like methane and ammonia. Oxygen levels increased significantly due to photosynthesis by blue-green algae and later plants, which split carbon dioxide (CO₂) and water (H₂O) to release oxygen.

So option 2 is correct.