Working independently, in the 1920s, Aleksandr Oparin and J. B. S. Haldane proposed similar theoretical schemes for how life may have originated on Earth (see life, origin). Hence, the term "Oparin-Haldane theory" is sometimes used when referring to their views. The main similarities and differences between Oparin's and Haldane's suggestions are summarized below. The first practical test of the Oparin-Haldane Theory was the Miller-Urey experiment, carried out in 1953.
|primitive atmosphere||Reducing, composed of methane, ammonia, hydrogen and water vapor||Reducing, composed of carbon dioxide, ammonia and water vapor|
|source of carbon for life||Methane||Carbon dioxide|
|site of prebiotic evolution||Atmosphere, then oceans||Atmosphere, then oceans|
|mechanism||Spontaneous appearance of coacervates followed by evolution to cell-like state||Synthesis of increasingly complex organic molecules in presence of ultraviolet light|