Chemical evolution

In one proposed scenario (referred to as chemical evolution), the first organisms arose from a four–stage process. The first stage of chemical evolution likely involved the abiotic (not of biological origin) synthesis of small organic molecules (monomers) such as amino acids and nucleotides. Ultraviolet light from the sun would easily have reached the surface of Earth (ozone did not exist at that time) and would probably have been the primary source of energy to drive these synthesis reactions.

In the second stage of chemical evolution, these monomers likely joined to form polymers. Two key polymers for any type of genesis of life would have been proteins and nucleic acids. In the third stage of chemical evolution, polymers would have aggregated into protobionts (Protobionts are systems that are considered to have possibly been the precursors to prokaryotic cells) , which would have been separate entities distinguishable from their surroundings.

Finally, these protobionts would have developed some type of heredity mechanism, hence the need for nucleic acids.