It probably contained hydrogen, nitrogen, carbon monoxide and carbon dioxide. Water would have been in liquid form at the beginning of life, formed from eons of rain washing minerals into the seas and torrential storms and lightening. He formed amino acids in less than a week. Other experimenters using gasses that may have been closer to earth's early gases have formed glucose, ribose, adenine, NAD, and other nucleotides using either electrical sparks or ultraviolet light in presumed early atmospheres. Clay particles may have been places where organic chemicals concentrated and formed more complex molecules.
Experiments show complex molecules forming on clay surfaces if alternately dried and wetted.
Another theory suggests the thermal vents of the ocean. A researcher duplicated these conditions and came up with the formation of small proteins. Proteins may have formed that promoted amino acid linking making more protein. Another theory has RNA, which can be self duplicating, promoting protein formations as it does today in ribosomes. The text describes a theoretical natural selection for enzymes that use up local simple chemicals.