![]() External sources of energy may have triggered these reactions, including lightning, radiation, atmospheric entries of micro-meteorites and implosion of bubbles in sea and ocean waves. The classic 1952 Miller–Urey experiment demonstrated that most amino acids, the chemical constituents of proteins, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. ![]() Researchers generally think that current life descends from an RNA world, although other self-replicating molecules may have preceded RNA. Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acids DNA and RNA for the mechanisms of heredity. It primarily uses tools from biology and chemistry, with more recent approaches attempting a synthesis of many sciences. The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. ![]() Many proposals have been made for different stages of the process. ![]() The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but an evolutionary process (i.e., a process of gradually increasing complexity) that involved the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. ![]() In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. Stages in the origin of life range from the well-understood, such as the habitable Earth and the abiotic synthesis of simple molecules, to the largely unknown, like the derivation of the last universal common ancestor (LUCA) with its complex molecular functionalities. ![]()
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