How did life originate? There are no witnesses who can actually describe what happened, and there is no direct evidence to investigate (BSCS). Answers to these questions took a large amount of time and investigation in order for scientists to come up with a sort of "semi" answer to these questions. Frankly, we can not answer them with complete assurance that the answer is indeed 100% correct. Yet, we can and will continue to try to decode the records held in the rocks of Earth and hope hat new data or new interpretations of old evidence will lead to answers (BSCS). These will consist of precursor molecules, biological molecules, proto cells, and advanced metabolism (BSCS).
In the 1920's, two men named Alexander Oparin and J.B.S. Haldine independently developed the first extensive hypothesis about how life may have originated (BSCS). Developing an idea called the Heterotroph Hypothesis, they assumed that life processes developed very gradually (BSCS). The first organisms were heterotrophs, while Autotrophs evolved later, and photosynthesis resulted in the oxygen - rich atmosphere of today (BSCS, MP). Both Oparine and Haldine's thoughts on the basis of the formation of life were different from each other, but both thought the first life on earth was heterotrophs (BSCS).
Two other scientists, named Harold Urey and Stanley miller worked on this problem about the basis of life in the 1950's. Stanley Miller created an apparatus where methane, hydrogen, and ammonia gasses circulated past an electrical spark. A container of water connected to the apparatus supplied heat and water vapor. As it cooled and condensed to "rain", Miller realized that he just created some of the conditions that may have been present in the early atmosphere (BSCS). Because of his experiment, he found out that Amino acids might have been present in the Early Earth, If amino acids were present in the early earth, then that meant precursor molecules did because amino acids are precursor molecules.