There was no free oxygen. There was no free oxygen because oxygen reacted to make water, iron, silicates, carbon dioxide, and carbon monoxide. In the 1950s it was shown that hydrogen, ammonia, methane gas, water, and lightning could produce organic compounds. In water these compounds dissolved and formed amino acids, sugars, purines, and pyrimidines- the building blocks of life. Polymerization - the generation of large molecules from smaller molecules.
Some polymers can reproduce themselves.
They found that some protists have Ribozymes - ribosomal RNA that catalyze chemical reactions. In the late 1970s RNA was found to replicate itself without the help of enzymes. Experiments showed that ribozymes function better in water. So life required a barrier to control internal conditions. In the 1920s a shaken mixture of large proteins and polysaccharides formed protobionts or coacervates - drops that are divided into two phases, an interior and an exterior.