『Abstract
　Carbonaceous matter (CM) from ca. 3.5 Ga hydrothermal black cherts of the Pilbara Craton of Western Australia and the Barberton Greenstone Belt of South Africa yielded transmission electron microscopy (TEM) images that are suggestive of microbial remains and possible remnants of microbial cell walls. These are compared to a potential modern analogue, the hyperthermophilic Methanocaldococcus jannaschii, derived from an active seafloor hydrothermal environment and cultured under similar conditions. A striking resemblance to the early Archaean forms was evident in wall structure and thermal degradation mode. Cell disintegration of the cultures occurred at 100℃ marking the limits f life. Complete disintegration, deformation and shrinkage occurred at 132℃. A multidisciplinary approach to the characterisation of the CM was undertaken using organic petrology, TEM coupled with electron dispersive spectral analysis (EDS), high resolution TEM (HRTEM) to determine molecular ordering, and elemental and carbon isotope geochemistry. Reflectance measurements of the CM to determine thermal stress yielded a range of values corresponding to several populations, and pointing to different sources and processes The δ¹³C values of Dresser Formation CM (-36.5 o -32.1‰) are negatively correlated with TOC (0.13-0.75％) and positively correlated with C/N ratio (134-569), which is interpreted to reflect the relative abundance of high Ro/oxidised/recycled CM and preferential loss of ¹²C and N during thermal maturation. TEM observations, inferred carbon isotopic heterogeneity and isotope fractionations of -27 to -32‰ are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM.

Keywords: Archaean; Pilbara Craton; Barberton Greenstone Belt; Carbonaceous matter; Methanocaldococcus jannaschii; Transmission electron microscopy; Carbon isotopes』

1. Introduction
2. General geology and methods of study
　2.1. Geological setting
　2.2. Sample processing
　2.3. Microbiological procedures
　2.4. Organic petrology
　2.5. Scanning and transmission electron microscopy
　2.6. Carbon isotope analysis
　2.7. Total organic carbon (TOC) and elemental analysis
3. Results
　3.1. Organic petrology
　3.2. Scanning and transmission electron microscopy
　3.3. Carbon isotopes and elemental composition
4. Discussion
　4.1. Temperatures obtained from reflectance (Ro)
　4.2. Comparison with an extant hyperthermophile
　4.3. Origin of CM from carbon isotopes and elemental composition
5. Conclusion
Acknowledgments
References