Evolution of O2 during photosynthesis :
In non-cyclic stage of photosynthesis in the light phage, O2 evolved from splitted water. If O2 was not relesed in the atmospher in the photosynthesis process, then there would be a great scarcity of O2 in the atmosphere. As a result the entire living creature would have perished because our respiratory system stops functioning for want of O2.
Carbohydrate is produced during photosynthesis. Plant reserved the excess carbohydrate after their requirements. For example: Paddy, Wheat, Maize, Barley, Potato, Sweet Potato, Sugarcane etc. We took these as food. If green plants do not manufacture carbohydrate in photosynthesis, then for want of food all of the members of Animal Kingdom including human beings would have been destroyed.
If there were no Sunlight on the Earth there will have no Photosynthesis. Without photosynthesis there would be no movement of energy. The earth would become motionless. Without Sunlight no living being could exist.