- Theory of the Origin of Life by A. I. Oparin
Proposed in 1924, by a Russian biochemist, Aleksandr Ivanovich Oparin, this theory stated that life originated from inorganic and organic compounds as a result of chemical evolution and environmental cues like heat, light, etc.
Oparin's theory was based on the idea that the early atmosphere of the Earth was reducing in nature and contained gases like methane (CH4), ammonia (NH3), water vapor (H2O), and hydrogen (H2). He proposed that these gases, through the influence of energy sources such as lightning, ultraviolet (UV) radiation from the sun, and volcanic heat, could have formed simple organic molecules.
Oparin argued that as the primitive Earth cooled, these simple molecules joined together to form complex organic compounds, such as amino acids, nucleotides, and sugars, which were the building blocks of life. Thus, the gradual progression from inorganic to organic molecules eventually led to the formation of the first primitive life forms.
Oparin's theory laid the foundation for understanding how life could have originated naturally from non-living matter and provided a framework for subsequent experiments in the field of abiogenesis, including those conducted by Stanley Miller and Harold Urey in 1953.