This is an advance summary of a forthcoming article in the Oxford Encyclopedia of Planetary Science. Please check back later for the full article.
Stanley Miller demonstrated, in 1953, that it was possible to form amino acids from methane, thus generating the ambitious hope that chemists would be able to shed light on the origins of life by recreating a simple life form in a test tube. However, it must be acknowledged that the dream has not yet been accomplished, despite the great volume of effort and innovation made by the scientific community.
At minimum, primitive life can be defined as an open chemical system, fed with matter and energy, capable of self-reproduction—that is, making more of itself by itself—and also capable of evolving. The concept of evolution implies that the chemical system transfers its information fairly faithfully, but makes a few random errors. By chance, some parts of the self-assembly are then capable of generating a copy. Sometimes, a minor error in the process of assembling generates a more efficient copy, which then becomes the dominant species. Two different materials for the assembled parts have been proposed: mineral or organic, the latter prompting a majority consensus among scientists.
In terms of this consensus, there are two schools of thought, each proposing the prebiotic supply of organics. The proponents of a metabolism first hypothesis call for the spontaneous formation of simple molecules from carbon dioxide and water to shortly generate life. In the second hypothesis, the primeval soup scenario, rather complex organic molecules accumulate in a warm little pond prior to the emergence of life. The proponents of the primeval soup, or replication first, are by far the more active. They have succeeded in reconstructing small-scale versions of proteins, membranes, and RNA. Quite different scenarios have been proposed for the inception of life: the RNA world, a vesicular origin, self–organization counteracting entropy, or a stochastic approach merging chemistry and geology. Understanding the emergence of life is a shared preoccupation in all these approaches.
Finally, the word origin can be understood as “origin-cause” but also as “origin-beginning”, which can then include panspermia. Although panspermia has been shown to be feasible, it has not received great attention, since it pushes life elsewhere (from outer space), without deciphering its origin.