Assertion : The primitive atmosphere was reducing one i.e. without oxygen.
Reason : In the primitive atmosphere, oxygen was involved in forming ozone layer.

If both assertion and reason are true and reason is the correct explanation of assertion

If both assertion and reason are true but reason is not the correct explanation of assertion

If assertion is true but reason is false

If both assertion and reason are false

Solution

If assertion is true but reason is false

The lightest atoms of nitrogen, carbon etc. formed the primitive atmosphere. Hydrogen atoms were most numerous and most reactive in primitive atmosphere. Hydrogen atoms combined with all oxygen atoms to form water leaving no free oxygen. Thus primitive atmosphere was reducing atmosphere (without free oxygen) unlike the present oxidising atmosphere (with free oxygen). Formation of ozone layer is the consequence of modern oxidizing atmosphere having plenty of free oxygen. As more oxygen accumulated in the atmosphere (due to photosynthesis) ozone began to appear in the top layers.

Some More Questions From Evolution Chapter

Arrange the following substances in a proper sequence with regard to the formation of chemical constituents at the time of origin of life :

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Evolution

Some More Questions From Evolution Chapter

Arrange the following substances in a proper sequence with regard to the formation of chemical constituents at the time of origin of life :

Sugar, methane, nucleic acid and amino acid.

What is the phenomenon called when the original drifted population becomes founders?

What are the two key concepts of Darwinian Theory of Evolution

What were the units of life according to the early Greek thinkers ?

Mention the type of nutrition in the cells originated first during the origin of life.

Which group of organisms were responsible for appearance of free oxygen in the atmosphere of the primitive earth ?

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What is the type of evolution in which the same structure developed along different directions due to adaptations to different needs ?

Name the different eras of geologic time scale.

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NCERT Sample Papers

Entrance Exams Preparation

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For Daily Free Study Material Join wiredfaculty

Evolution

Some More Questions From Evolution Chapter

Arrange the following substances in a proper sequence with regard to the formation of chemical constituents at the time of origin of life : Sugar, methane, nucleic acid and amino acid.

What is the phenomenon called when the original drifted population becomes founders?

What are the two key concepts of Darwinian Theory of Evolution

What were the units of life according to the early Greek thinkers ?

Mention the type of nutrition in the cells originated first during the origin of life.

Which group of organisms were responsible for appearance of free oxygen in the atmosphere of the primitive earth ?

What is meant by the term fossil ?

What is the type of evolution in which the same structure developed along different directions due to adaptations to different needs ?

Name the different eras of geologic time scale.

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

Arrange the following substances in a proper sequence with regard to the formation of chemical constituents at the time of origin of life :

Sugar, methane, nucleic acid and amino acid.