Answer: Oparin is credited with the idea that early life formed through a series of chemical reactions that make simple compounds more complex.
Explanation:
Urey and Miller conducted experiments to test the chemical origin of life by creating the similar conditions as were predicted to exist.
Oparin found that simple organic compounds were changed by heat and solar radiation into more complex organic compounds.
Darwin gave the theory of evolution and declared that species survived through a process known as natural selection, where those that successfully adapts or evolves to meet the changing requirements of their natural habitat thrives, while those that failed to evolve and reproduce dies.