Japan Geoscience Union Meeting 2016

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International Session (Oral)

Symbol B (Biogeosciences) » B-AO Astrobiology & the Origin of Life

[B-AO01] Astrobiology: Origins, Evolution, Distribution of Life

Tue. May 24, 2016 3:30 PM - 5:00 PM A01 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Kensei Kobayashi(Department of Chemistry and Biotechnology, Faculty of Engineering, Yokohama National University), Akihiko Yamagishi(Tokyo University of Pharmacy and Life Science, Department of Molecular Biology), Masatoshi Ohishi(Astronomy Data Center, National Astronomical Observatory of Japan), Eiichi Tajika(Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo), Takeshi Kakegawa(Graduate School of Science, Tohoku University), Shigeru Ida(Department of Earth and Planetary Science, Graduate School of Science and Technology, Tokyo Institute of Technology), Mary Voytek(NASA Headquarter), Joseph Kirschvink(Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA), Chair:Eiichi Tajika(Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo), Takeshi Kakegawa(Graduate School of Science, Tohoku University)

4:15 PM - 4:30 PM

[BAO01-10] Big Bang of life: unique composition of organic molecules at >3.95 Ga

*Kunio Kaiho1, Ryosuke Saito1, Tsuyoshi Komiya2, Wladyslaw Altermann3, Martin Van Kranendonk4 (1.Graduate School of Science, Tohoku University, 2.University of Tokyo, 3.University of Pretoria, 4.University of New South Wales)

Keywords:early life, organic molecules, Late Heavy Bombardment, Archean

The earliest life on Earth may have appeared at approximately 4.0 billion years ago (Ga) based on analyses of molecular clocks. However, there is no evidence of early life between 4.0 and 3.7 Ga. The type of the earliest life is also unknown. Here, we report that organic molecules derived from the earliest life have been detected from the oldest shallow-sea sedimentary rocks from Labrador, Canada, the age of which is >3.95 Ga. These molecules have two unique features: (1) branched alkanes (methyl- and ethyl-) and squalane exclusively dominate in these rocks; (2) n-alkanes and branched alkanes possess strong even-over-odd predominance in the number of carbons. These features have not been found in strata younger than 3.5 Ga. Among these molecules, it is difficult for squalane to be produced by non-biological processes. The dominance of squalane, which is derived from squalene, a constituent of archaeal lipid and precursor of both eukaryotic (sterol) and prokaryotic (hopanoid) lipids, suggests that this is a fundamental organic molecule of life common to all three domains, i.e., prokaryotes, archaea, and eukaryotes. This unique composition changed to a more normal composition between >3.95 Ga and 3.48 Ga. This change looks like dawn of the universe, i.e. Big Bang, because the unique type of life that occurred during this first short period of <0.5 billion years was followed by the current type of life that has persisted for >3.5 billion years. Giant impact of asteroids on Earth occurred between 4.03 and 3.85 Ga (Late Heavy Bombardment) evidenced by ages of impact craters of the moon. Those impacts could have eradicated the early life found in Labrador followed by emergence of the current type of life on Earth.