Which of the following theories suggests that life originated on earth by combinations of various chemicals through constant chemical reactions over a long period?

The correct answer is: Theory of chemical evolution

• Theory of chemical evolution states that complex organic molecules were made from simple organic compounds by the chemical reactions.
• The theory was based on the experiment done by Miller and Urey .
• They made the similar condition as that of early earth by using water, ammonia and hydrogen 
• On reaction organic molecules were produced 
• The end products of the reaction was aldehyde and amino acids which are the precursors of nucleic acid.  Hence , complex organic molecules were made from simple molecules by the chemical reactions