- A Life is understood under this theory to have arrived on early Earth from outer space aboard comets or meteorites, with the necessary organic monomers having been largely assembled before ever reaching the planet's surface
- B Life arose from chemical evolution in the primitive ocean: simple inorganic molecules → organic monomers (abiotic synthesis) → polymers → protocells → first cells with self-replication; early Earth had reducing atmosphere (no O2)
- C Life is proposed under this theory to have usually existed on Earth in an unchanging steady state since the planet formed, with little chemical evolution of monomers, polymers, or protocells ever taking place in the primordial ocean
- D This theory holds that a divine creator directly and instantaneously created the first living cells on early Earth, without any gradual chemical evolution of simple molecules into self-replicating protocells over time
Correct answer: B. Life arose from chemical evolution in the primitive ocean: simple inorganic molecules → organic monomers (abiotic synthesis) → polymers → protocells → first cells with self-replication; early Earth had reducing atmosphere (no O2)
Explanation: Oparin (1924) and Haldane (1929) independently proposed: (1) Early Earth: reducing atmosphere (H2, NH3, CH4, H2O); no free O2; (2) UV light and lightning energy drive synthesis of organic molecules; (3) Molecules accumulated in 'warm little pond' (primordial soup) or deep sea vents; (4) Polymers formed on mineral surfaces; (5) Self-replicating molecules (RNA world hypothesis); (6) Membrane formation → protocells → first cells.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.