Abiogenesis

Abiogenesis is the emergence of life from nonliving chemical systems. It investigates how chemical processes could produce self-maintaining, evolving systems.

RNA world hypothesis: The hypothesis that RNA preceded DNA and proteins as both genetic material and a catalyst in early life. It offers a route from chemical replication to heredity before modern cells existed.
Life: A self-maintaining chemical system capable of evolution through variation and heredity. A workable definition of life sets the threshold abiogenesis must explain.
Miller–Urey experiment: A 1953 experiment that produced amino acids by applying electrical discharges to gases intended to model early Earth. It demonstrated that biologically relevant molecules can form from simpler compounds under simulated conditions.
Evolution: The change in inherited traits of populations across generations. Evolution explains diversification after heredity exists, whereas abiogenesis concerns life’s initial emergence.
Metabolism-first hypothesis: The proposal that self-sustaining chemical reaction networks arose before genetic replication. It reverses the RNA-first sequence by making organized chemistry precede genes.
Chemical evolution: The gradual increase in chemical complexity through reactions among nonliving substances. It describes the transition from simple compounds toward systems with life-like properties.
Amino acid: An organic molecule that serves as a building block of proteins. Amino acids formed in prebiotic experiments show one route to biological building blocks.
Panspermia: The hypothesis that life, or its precursors, reached Earth from elsewhere in space. It relocates life’s arrival but does not by itself explain how life first originated.
Protocell: A simple, cell-like structure proposed as an intermediate in the origin of life. Membrane-bounded compartments could concentrate reactants and enable primitive heredity.
Nucleic acid: A polymer, such as DNA or RNA, that stores or transmits biological information. Information-bearing polymers are candidates for the heredity required by evolving life.

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