1) A reducing atmosphere from volcanic outgassing,
2) High-temperature submarine vents and fumaroles -- black smokers, and
3) Space--for example, the 4.6 billion-year-old Murchison meteorite, discovered in Australia in 1969 was loaded with amino acids, aliphatic and aromatic hydrocarbons, hydroxy acids, purines, pyrimidines, and other chemical building blocks of life.
'The evidence strongly suggests that prior to the origin of life the primitive Earth already had many different catalytic agents, polymers with sequences of nucleotides, and membrane-forming compounds,' Lazcano concluded. This prebiotic soup led to a catalytic and replicative RNA world, which led to the DNA world of today."