演題者：Juske Horita (Texas Tech.)
講演タイトル：In Search of Carbon Isotope (a)Biosignatures
6/22 (木) 11:00より @MISHIMA Hall
A modern Earth is characterized by a plethora of biological activities, which makes the detection of abiogenic organic molecules, if any, a case of needles in haystacks. On contrary biogenic organic matter had been very scarce in an early Earth with life still in its infancy. The idea of using stable isotope compositions of light elements, particularly of carbon, as a sign of (non)biological activities, (a)biosignatures, both present and past, dates back to the dawn of stable isotope geochemistry in the 1940s. In the wake of the discovery of large variations in 13C/12C ratios among various carbon-bearing materials including plants, the contentious debate ensued between Kalervo Rankama and Harmon Craig in the early 1950s whether the origin of graphitic carbon in ancient rocks (biogenic vs. abiogenic) can be uniquely identified by its isotopic compositions. The renewed debates in the late 1990s to the early 2000s on the origin of graphitic and organic carbons from Early Archean rocks from Australia and Greenland were very much reminiscent of the Rankama–Craig debate half a century apart. In the last decade, rapid developments of novel analytical techniques (intramolecular isotope analysis, both clumped and position-specific) and the flourish of astrobiology have been driving us to develop new criteria for carbon isotope (a)biosignatures in both terrestrial and extraterrestrial environments. Here, an attempt is made to review briefly the history of isotope biosignatures and to assess our current knowledge of carbon isotope (a)biosignatures.
