In 1924 Alexander Oparin hypothesized that organic compounds were formed in the early earth when the high energy provided by UV Rays, and storms, caused different molecules to react, and create new organic compounds, such as Amino Acids DNA, and RNA.
In the early 1950s, Professor Harold Urey and one of his students, Stanley Miller, began experimenting to prove Oparin's theory. Miller built an apparatus which circulated gasses likely to be present in the early atmosphere (Methane (CH4), Ammonia (NH3), Water (H2O), and hydrogen (H2) ) past an electrical discharge, simulating the UV Rays and violent electrical storms present in the early atmosphere.
After allowing the experiment to continue for a week, the results where startling. The previously colorless solution inside the apparatus had turned red. Upon analyzing the solution, Miller found many organic molecules present, some of which couldn't be readily identified. The most important of created compounds, however, where amino acids. This, in effect, proved Oparin's theory that organic compounds could have been created in the early atmosphere. Further studies showed that some amino acids would have combined with hydrogen cyanide (HCN), which is a byproduct of volcanic activity. This combination would form purines and pyrinidines, which are used to make nucleic acids, which in turn create DNA.
After these compounds had been created on the early earth, the earth eventually began to cool. Water vapor the condensed, which formed vast oceans, seas and lakes, in which simple organic molecules began to accumulate for millions of years, producing an "organic soup" of sorts. The amino acids would have then polymerized (which means they formed chains, such as proteins. The most likely theory as to how the amino acids combined is that they where washed up into clay/rock depressions on land, where the water evaporated, leaving behind concentrated organic compounds in high heat.
Sidney W. Fox set out to prove this. He took a mixture of approximately 20 different amino acids, and heated then to the melting point. When they cooled, Fox observed that they had polymerized into proteins.
But how did these proteins and other organic compounds form the first cell? Most likely, a group of organic molecules including proteins, and primitive fatty acids formed into a droplet, or bubble-like structure, which had the ability to combine with external elements, such as proteins not a part of it. Eventually, these droplets would grow, and divide. These droplets would eventually evolve into the first true cell. These early cells would have been autotrophs, which are organism which produce their own energy, usually from sunlight. Some of these cells would then evolve into heterotrophs (organisms which ingest organic material as a nutrient source)