Metabolism first: Iron–sulfur world
Main article: Iron–sulfur world hypothesis
A series of experiments starting in 1997 showed that early stages in the formation of proteins from inorganic materials including carbon monoxide and hydrogen sulfide could be achieved by using iron sulfide and nickel sulfide as catalysts. Most of the steps required temperatures of about 100 °C (212 °F) and moderate pressures, although one stage required 250 °C (482 °F) and a pressure equivalent to that found under 7 kilometres (4.3 mi) of rock. Hence it was suggested that self-sustaining synthesis of proteins could have occurred near hydrothermal vents. ^{[70]}
Metabolism first: Pre-cells (successive cellularization)
In this scenario, the biochemical evolution of life ^{[70]} led to diversification through the development of a multiphenotypic population of pre-cells, ^{[67][68][69]} i.e. evolving entities of primordial life with different characteristics and widespread horizontal gene transfer.
Early diversification of life with Kandler's pre-cell theory (Kandler 1998, p. 22) ^{[69]}
From this pre-cell population the founder groups A, B, C and then, from them, the precursor cells (here named proto-cells) of the three domains of life ^{[71]} arose successively, leading first to the domain Bacteria, then to the domain Archea and finally to the domain Eucarya.