How might chemosynthetic organisms scientists to understand how life developed on earth?

Organisms that are chemosynthetic process chemosynthesis. It is a series of chemical reactions that convert the energy in food into ATP. In contrast to photosynthesis which is using sunlight to convert and create food from the gained resources such as water, carbon dioxide and the sunlight, itself.
These two process differ from which the product they process or undergo to produce food and converted into energy for the cell to use in its many cellular activities. 

Ibelieve the answer is c.