Question

According to one of the most widely accepted theories, earth's atmosphere before origin of life was

• A. oxidizing
• B. oxidizing along with $H_2$
• C. reducing with $O_2$ in small amount
• D. reducing with oxygen absent in $O_2$ form

Answer 1

The correct option is D reducing with oxygen absent in $O_2$ form

The Earth formed around 4.5 billion years ago. Scientists believe that its early atmosphere was produced by volcanic activity. Due to volcanic eruptions, molten mass covered the surface of the Earth. Various gases like methane, ammonia, carbon dioxide and water vapour were released from the molten mass.

The ultraviolet radiation broke water into oxygen and hydrogen. Hydrogen being lighter escaped. Oxygen combined with ammonia and methane to form water, carbon dioxide and other compounds.

Earth’s primitive atmosphere was rich in methane, ammonia, water vapour, but it lacked free oxygen.

Hence, free oxygen was almost nil in the primitive atmosphere. Therefore, the atmosphere in early or primitive earth was reducing unlike today’s oxidising atmosphere.