Question

Describe the steps by which simple inorganic substances may have undergone chemical evolution to yield complex organic molecules that could eventually form living matter.

Answer 1

1. Origin of Earth and Primitive Atmosphere: The early Earth formed with a hot molten surface and a primitive atmosphere composed mainly of simple inorganic gases like hydrogen, ammonia, methane, water vapor, carbon dioxide, and nitrogen, but essentially without free oxygen.

2. Formation of Simple Inorganic Molecules: As the Earth cooled from very high temperatures, these gases formed simple inorganic compounds including oxides, carbides, nitrides, and superheated steam (water vapor). Condensation cycles and volcanic activity created seas with dissolved inorganic molecules.

3. Abiotic Synthesis of Organic Compounds: In the absence of oxygen, simple inorganic molecules underwent chemical reactions, energized by lightning, UV radiation, and heat. Hydrocarbons formed and reacted with steam to produce oxygen- and hydroxy- derivatives such as aldehydes, ketones, and acids. These, through further condensation and polymerization, yielded a variety of organic molecules,sugars, glycerol, fatty acids, amino acids, and nitrogenous bases (purines and pyrimidines). These organics accumulated in the “primordial soup” of the oceans.

4. Polymerization into Macromolecules: The simple organics combined into more complex polymers such as polysaccharides, proteins (polypeptides), nucleotides, and ultimately nucleic acids (RNA/DNA). Some polypeptides had catalytic properties akin to primitive enzymes.

5. Formation of Coacervates and Colloids: The macromolecules aggregated into colloidal droplets called coacervates, which exhibited some characteristics of living systems such as selective absorption and growth. Fatty acids or lipids formed limiting membranes around these droplets, creating proto-cell-like structures.

6. Emergence of Autocatalytic Systems and Genetic Material: Inside these structures, molecular systems capable of self-replication and metabolism,autocatalytic cycles and primitive genes,arose, marking the birth of molecular individuality and life-like processes.

7. Origin of Primordial Cells (Prokaryotes): These protobionts evolved into true cellular forms (prokaryotes) capable of metabolic activities and replication.

8. Diversification of Metabolic Pathways: From these early anaerobic heterotrophs, autotrophic organisms arose that could synthesize organic molecules from inorganic carbon sources using chemical or light energy, eventually leading to oxygenic photosynthesis and the evolution of more complex life forms.