MP Board · Class 12 · Biology · EvolutionQuestion 3\nDescribe the Miller-Urey Experiment that provided experimental evidence for the Chemical Evolution of Life (Oparin-Haldane Hypothesis).\nStructure your answer under the following headings: Objective / Principle Experimental Setup and Conditions Observations Conclusion and Significance

1. Objective / Principle

• The experiment was performed in 1953 by Stanley Miller and Harold Urey.
• Objective: To test the Oparin-Haldane hypothesis experimentally, which proposed that the first form of life arose from non-living organic molecules formed from inorganic precursors under reducing primitive Earth conditions (Chemical Origin of Life / Abiogenesis).

2. Experimental Setup and Conditions\nMiller recreated the conditions believed to exist on primitive, prebiotic Earth inside a closed glass apparatus:

• Gaseous Mixture: A sealed glass flask was filled with a mixture of gases representing the primordial atmosphere: Methane ($CH_4$), Ammonia ($NH_3$), Hydrogen ($H_2$), and Water vapor ($H_2O$) in the ratio $2:2:1$.
• Energy Source: Electric discharge (sparks) was generated using electrodes at $800^\circ C$ to simulate lightning storms that provided energy on early Earth.
• Water Reservoir and Heating: Water was boiled in a lower flask to continuously supply water vapor into the system.
• Condenser: A cooling condenser was attached to cool down the gases and collect the condensed liquid into a trap.
• Duration: The apparatus was run continuously for about one week.

3. Observations

• After a week, the clear water in the trap turned dark brown and turbid.
• Chemical analysis of the collected liquid revealed the synthesis of several organic compounds:
  • Amino Acids: Glycine, Alanine, and Aspartic acid.
  • Organic Acids: Formic acid, Acetic acid, Lactic acid, and Succinic acid.
  • Later similar experiments by other scientists also yielded purines, pyrimidines, sugars, and pigments.

4. Conclusion and Significance

• Conclusion: The experiment successfully proved that organic monomers like amino acids, which are essential building blocks of life, could be synthesized abioticly under primitive Earth conditions.
• Significance:
  • Provided concrete, empirical proof supporting the Chemical Evolution theory of life.
  • Confirmed that life originated from non-living inorganic matter through progressive chemical reactions.