Answer:
Oxygen gas
Explanation:
Oxygen is the most essential gas that supports life. In the early atmosphere, during the time of the formation of the earth, there was the absence of this gas. But after a certain period of time, roughly about 2.3 billion years back, there was slightly an increase in the atmospheric oxygen that helped in the origin of life, forming unicellular organisms such as cyanobacteria and blue-green algae.
These organisms were present in the water bodies that carried out the process of photosynthesis, by absorbing CO₂ gas in the presence of sunlight and liberating O₂ gas. This, over millions of years, led to the evolution of life and created more complex multicellular organisms.
Thus, Oxygen is highly essential for the origin of life on earth.
