Answer:
Sources
of oxygen in the atmosphere:
(i) Early in the evolution of the Earth, oxygen is believed to have been
released from water vapour by ultra-violet radiations and accumulated in the atmosphere
as the hydrogen escaped into the outer layer of the Earth's atmosphere.
(ii) The main driving factor of the oxygen cycle in which
water and carbon dioxide combine in the presence of sunlight and chlorophyll to
form glucose and oxygen by the process of photosynthesis.
(iii) Molecular oxygen is mainly contained in rocks and
minerals.
(iv) Molecular oxygen is also released in the atmosphere
by the process of photolysis.
(v) The weathering process initiated by organisms can also
free the oxygen from the lithosphere.
(vi) Plants and animals extract nutrient minerals from
rocks and release oxygen in the process.
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