Question

Statement 1 : In due course of evolution, the number of photoautotrophs increased and enormous amounts of oxygen was released in the sea and primitive atmosphere.

Statement 2 : This oxygen then reacted with methane and ammonia leading to transform them into carbon dioxide and free nitrogen.

• A. Both the statements are correct
• B. Statement 1 is correct and statement 2 is incorrect
• C. Statement 1 is incorrecta and statement 2 is correct
• D. Both the statements are incorrect

Answer 1

The correct option is A Both the statements are correct

Atmosphere of the early Earth was highly reduced, there was no oxygen present in the primitive earth atmosphere until simple organisms like cyanobacteria evolved the capability to carry out the process of photosynthesis. Oxygen became a component of the atmosphere almost 2 billion years after the earth was formed.
Simple molecular oxygen is utilised by most living things in order to create energy.
Photoautotrophs evolved on the earth, the process of photosynthesis started and oxygen generation started. As the number of photoautotrophs increased, oxygen was released into the sea and atmosphere. The free oxygen then started reacting with methane and ammonia and transformed them into carbon dioxide and nitrogen.
Because there was no oxygen in the early atmosphere, the earth lacked the blanketed layer called the ozone layer that protects the earth from ultraviolet radiation. When oxygen evolved in the atmosphere, ultraviolet light changed some of the oxygen into ozone. This ozone molecule later formed a blanketed layer on earth protecting it from harmful radiation and allowing visible light as the main source of energy.