Which of the following was not found in free form during origin of life?
A
Ammonia
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B
Methane
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C
Oxygen
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D
Hydrogen
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Solution
The correct option is C Oxygen The primitive reducing atmosphere of earth was rich in water vapour, carbon monoxide, carbon dioxide and hydrogen. Hydrogen was present in abundance.
Absorption of infrared radiation by greenhouse gases (CO2 and CH4) imparted high temperature to primitive earth. The high temperature, UV light and lightening facilitated reaction between above mentioned elements. Oxygen did not occur in free state as the prevailing reduced substances immediately combined with it to form oxides (iron oxides, silicon oxides). Abundant hydrogen combined with free oxygen, nitrogen and carbon to form water, ammonia, methane and cyanides.