Essential Facts for NEET

Proposers of Chemical Evolution:

• Alexander Oparin (Russian, 1924) — primordial soup theory
• J.B.S. Haldane (British, 1929) — independently proposed similar idea
• Both agreed: life arose from inorganic molecules in a reducing atmosphere without free O2

Miller-Urey Experiment (1953):

• Scientists: Stanley Miller and Harold Urey
• Reactants: CH4 (methane), NH3 (ammonia), H2 (hydrogen), H2O (water vapour)
• Energy source: Electric sparks (simulated lightning)
• Absent substance: Free O2 — the atmosphere was REDUCING
• Duration: One week
• Products: Amino acids (glycine, alanine named) and other simple organic molecules
• Apparatus: Closed glass system with boiling flask and discharge chamber

What the Experiment Proved:

• Amino acids can form ABIOGENICALLY (without living organisms) under conditions resembling early Earth
• This is SUPPORT for Oparin-Haldane's chemical evolution hypothesis
• It is NOT proof that life originated this way — amino acids ≠ living organisms

Why the Reducing Atmosphere Matters:

• Free oxygen would have oxidized (destroyed) organic molecules as they formed
• Today's oxidizing atmosphere (with O2) would not allow this type of abiogenic synthesis
• The early Earth's atmosphere was fundamentally different from today's

NEET Traps to Avoid:

• Do NOT confuse Miller-Urey (amino acids) with Griffith's experiment (bacterial transformation) or Hershey-Chase experiment (DNA as genetic material)
• Products are amino acids, NOT nucleotides, DNA, or complete proteins
• Energy source is electric discharge (lightning), NOT UV radiation or heat alone

Beyond Miller-Urey:

• Modern RNA World Hypothesis: RNA may have been the first self-replicating molecule (can store information + catalyse reactions)
• Coacervates (Oparin): protein-lipid droplets that could concentrate organic molecules before true cells existed