Application of Stable Carbon Isotopes to Early Biochemical Evolution on Earth

Abstract

The emergence and early evolution of life on Earth have long been intriguing subjects for scientific inquiry and a continuous source of intel­ lectual excitement. Current work at this frontier proceeds along a number of different avenues and comprises a variety of disciplinary approaches that together strongly suggest that the Earth was inhabited by life as early as almost 4 Gyr ago. The present state of the field as inferred from the results of a broad interdisciplinary approach has recently been summarized by J. W. Schopf and coworkers (cf. Schopf 1 983). It is with the advantage of such a synoptic view that the present review addresses a single facet of the theme-namely, the potential isotopic infer­ ences of the presence of CO2-fixing (autotrophic) organisms for the carbon cycle of the early Earth. With biologically derived (organic) carbon as well as carbonates (limestone, dolomite, etc.) abundantly preserved in sediments, relevant isotopic evidence should have been encoded in the geologic record from its onset about 3.8 Gyr ago. It has been known since the pioneering studies by Nier & Gulbransen (1939), Murphey & Nier (1941), and Rankama (1948) that the trans­ formation of inorganic carbon into living matter entails a marked bias in favor of the light isotope C2C), with the heavy species (l3C) retained in the inorganic reservoir. Subsequent work performed by many investigators (e.g. Craig 1953, Park & Epstein 1960) has confirmed that all common