A variety of geologic and environmental settings have been proposed for an origin of life. These theories are often in competition with one another as there are many differing views of prebiotic compound availability, geophysical setting, and early life characteristics. The first organism on Earth likely looked different from LUCA. Between the first appearance of life and where all modern phylogenies began branching, an unknown amount of time passed. Within this time, unknown gene transfer, extinctions, and evolutions may have occurred, creating adaptations for a more diverse amount of environmental niches. One notable shifts is the one from an RNA-based to an RNA-DNA-protein world. There is more known about LUCA than the first organisms due to genomic reconstructions based on modern phylogenies.
The most popular hypotheses for settings in which an origin of life are possible are deep sea hydrothermal vents and surface bodies of water. Surface waters can be broken down into hot springs, moderate temperature lakes and ponds, and cold settings.