Figure 2

The prediction of the conditions for the emergence of complexity and life from the depth of chemical time. (a) Any kind of metabolite (Mi) involved in a proto-metabolic process must be protected by kinetic barriers to avoid side-reactions (yielding side-products as SPi) or direct reactions to products annihilating features of organization (catalysis, autocatalysis). These barriers help in holding the system far from equilibrium, which is a prerequisite for self-organisation. (b) Transition state theory is used here to predict the heights of these kinetic barriers at given values of the absolute temperature T and for a range of half- lives of the metabolite. Therefore, a requirement for the emergence of complexity and life is established from this relationship connecting the height of the barrier to the lifetime of chemical intermediates for a given absolute temperature. Thirty orders of magnitude separate the lifetime of a transition state (a vibration lasting a fraction of picosecond) from that of the universe (13.7 billion years). A representative range of 1 s to 100 years (more than nine orders of magnitude or ca. 30% of the full logarithmic scale) is selected as realistic for chemical intermediates that accumulate in protometabolic processes. (c) Because of the logarithmic dependence, this wide range of lifetimes corresponds to barriers spanning only from 74 to 129 kJ mol^–1 at moderate temperature (300 Kelvin). The domain of stability of liquid water (from the liquid state at low temperatures and high pressure to the critical point of water, blue area) and that in which forms of extant life on Earth are capable of growth (green area) are also displayed showing that the emergence of life was less unlikely at values of the temperature close to that of the fusion of ice.