Since their discovery in the late 1970s, deep-sea hydrothermal systems have been considered as likely candidates for the origin and early evolution of life on Earth. However, while subsequent investigations have revealed a great diversity of modern deep-sea hydrothermal ecosystems, they have done little to shed light on the issues of the origin and early evolution of life, metabolism, cells, or communities. Phylogenetic, biochemical and geochemical clues all seem to point to the early evolution of hydrogenotrophic chemolithoautotrophy such as methanogenesis and sulfurreduction, thus pinpointing the availability of hydrogen as one of the key elements needed for the early evolution of earthly life. Hydrogen-driven, photosynthesis-independent communities are very rare on the contemporary Earth, however, being unambiguously found only in subsurface environments of H₂-dominated hydrothermal systems. Such systems have been termed hyperthermophilic subsurface lithoautotrophic microbial ecosystems (HyperSLiMEs) (Takai et al., 2004; Nealson et al., 2005). The supply of abundant hydrogen and available inorganic carbon sources to power such communities is most likely coupled to hydrothermal serpentinization of ultramafic rocks and input of magmatic volatiles, both of which are related to specific geological settings. We propose here, on the basis of findings in the modern Earth and implications for the deep-sea hydrothermal systems in the Archean Earth, that “Ultramafics-Hydrothermalism-Hydrogenesis-HyperSLiME”, a linkage we refer to as Ultra H³, provided a suitable habitat for the early microbial ecosystem on the Archean Earth.