Boreskov

OP‐3HOT ABIOGENESIS AND EARLY BIOSPHERIC EVOLUTIONHelen Piontkivska 1 , Charles H. Lineweaver 2 and David W. Schwartzman 31 Department of Biological Sciences, Kent State University, USA2 Planetary Science Institute, Australian National University, Australia3 Department of Biology, Howard University, USA, dschwartzman @gmail.comWe argue that hyperthermophilic abiogenesis leading to a hyperthermophilic LastUniversal Common Ancestor (LUCA) of life is supported by a wide range of recent research.If the ambient ocean during abiogenesis was cold, then primitive mesophiles should haveemerged. The absence of deeply‐rooted mesophiles in molecular phylogenetic treessuggests that either primitive mesophiles did not survive a near sterilizing event in theHadean or a hot Archean climate, or alternatively did not emerge because of a hot Hadeanclimate. Drawing on a plausible scenario of hydrothermal abiogenesis near the seafloor((Russell and Hall 1997; Koonin and Martin 2005; Russell 2007), we propose that a spectrumof Bacterial and Archaeal protocells, including ancestors of extant prokaryotes, emergedsimultaneously in the redox potentials of a thermal gradient between a hydrothermal sourceon the seafloor and the ambient climatic oceanic temperature in Hadean time. Thetransition from RNA to DNA and the efficient repair of single and double strand breaks inDNA, rather than being the result of a mesophile to hyperthermophile transition could be aconsequence of the protocell emergence in a high temperature and high radiationenvironment due to intracellular K 40 and C 14 . Therefore the early accumulation of neutral‘‘clock‐like’’ substitutions could plausibly be driven by this radiation dose as a function oftime, with the surviving record having the potential of providing the time of emergence ofthe earliest metabolisms. The strong anti‐correlation of maximum growth temperatures(Tmax) of thermophiles with their rRNA and tRNA phylogenetic distances from the LCAsupports their Tmax being close to the environmental temperature of each organism atemergence. A climatic temperature close to 70‐ 80 deg C in the late Hadean/Archean isconsistent with paleotemperatures derived from oxygen isotopes in marine cherts ((Knauth,2005), and the measurement of melting temperatures of proteins resurrected fromsequences inferred from robust molecular phylogenies (Gaucher et al., 2008).[1]. Gaucher, E.A., Govindarajan S. and O.K. Ganesh, 2008, Palaeotemperature trend for Precambrian lifeinferred from resurrected proteins. Nature 451: 704‐707.[2]. Knauth LP. 2005. Temperature and salinity history of the Precambrian ocean: implications for the courseof microbial evolution. Palaeogeogr. Palaeoclimatol. Palaeoecol. 219:53–69.[3]. Koonin EV, Martin W. 2005. On the origin of genomes and cells within inorganic compartments. TRENDS inGenetics Vol.21 No.12, 647‐654.[4]. Russell MJ, Hall AJ. 1997. The emergence of life from iron monosulphide bubbles at a submarinehydrothermal redox and pH front. Jour. Geol Soc. London.154: 377‐402.[5]. Russell MJ. 2007. The Alkaline Solution to the Emergence of Life: Energy, Entropy and Early Evolution. ActaBiotheoretica doi:10.1007/s10441‐007‐9018‐5.34