Name one source of energy which was used for
Chemical combination in primitive atmosphere

Explanation:

Considering the atmosphere of the primitive earth to have contained water vapor, carbon dioxide, carbon monoxide, methane, and ammonia and/or nitrogen, then in the presence of an energy source, such as sunlight or lightning, a number of small molecules like hydrogen cyanide, HCN, are formed.

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."