Question

before there was life on earth which gas was absent from the ancient atmosphere?

Answer 1

oxygen.............................

Answer 2

Oxygen is the gas which was absent before there was life on earth and in ancient atmosphere.

Ancient atmosphere consisted of methane, ammonia, carbon monoxide, hydrogen sulphide etc.

This atmosphere is also described as reduced atmosphere due to the lack of oxygen.

This reduced atmosphere resulted in the volcanic activity on earth's surface.