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Step-by-Step Explanation
Step 1: Synthesis of Organic Monomers (II)
According to the widely accepted Oparin–Haldane hypothesis on the origin of life, the early Earth had a reducing atmosphere consisting of gases like methane, ammonia, hydrogen, and water vapor. Under the influence of energy sources such as UV radiation and lightning, these simple gases reacted to form small organic molecules (monomers). Experiments, such as the Miller–Urey experiment, provided evidence that organic monomers (e.g., amino acids) could indeed form from inorganic primordial compounds.
Step 1: Synthesis of Organic Polymers (III)
Once these monomers were present, they began combining under primitive Earth conditions to form larger and more complex organic molecules (polymers). For instance, amino acids linked together to form peptides and proteins, or nucleotides joined to form nucleic acid-like structures. This step marks the transition from simple, small building blocks to more complex macromolecules with diverse functional properties.
Step 1: Formation of Protobionts (I)
Protobionts (sometimes referred to as “coacervates” or “protocells”) are aggregates of abiotically produced organic molecules surrounded by a membrane-like structure. These structures maintained a distinct internal environment and could concentrate specific molecules, paving the way for the first steps toward a living system. Protobionts are considered precursors to true cells because they exhibit rudimentary metabolic processes and a boundary to separate the internal environment from the external world.
Step 1: Formation of DNA-based Genetic Systems (IV)
The last major step in the origin of life was the emergence of self-replicating genetic material. Initially, RNA is proposed to have played a central role (the RNA-world hypothesis), but eventually, organisms developed DNA-based genetic systems for more stable information storage and more accurate protein synthesis. The transition to DNA offered reliability and fidelity in replication, marking the crucial step toward modern biological systems.
Conclusion
Hence, the correct sequence of events as per our best scientific understanding of the origin of life is:
Synthesis of organic monomers (II)
Synthesis of organic polymers (III)
Formation of protobionts (I)
Formation of DNA-based genetic systems (IV)
