The appearance of living systems on Earth from non-living molecules is called chemical evolution.
Chemical evolution refers to the creation of living systems (complex organic molecules) from non-living (inorganic) molecules through chemical reactions on the primitive earth. Based on a theory, chemical evolution is said to occur in four stages which are; (i) simple organic substances, such as amino acids are formed by molecules in the primitive environment, (ii) the simple organic molecules combine and accumulate to form larger structures (such as proteins), (iii) the larger molecules interact to form structures called protobionts and (iv) protobionts evolve reproduction ability and transmit genetic instruction from one generation to another.