The Chemical Evolution Theory of the origin of life was proposed independently by A. I. Oparin and J. B. S. Haldane.

A. I. Oparin — Russian scientist, proposed the theory in 1924.

J. B. S. Haldane — British scientist, independently proposed a similar idea in 1929.

The theory states that life originated gradually from simple inorganic substances → complex organic molecules → primitive living organisms under early Earth conditions.