Biogenesity of carbonaceous, cyanobacteria-like materials found in the ~3.5Ga chert (e.g., Schopf, 1993) has been challenged, with an opposing interpretation of non-biological, post-depositional origin (e.g., Brasier et al., 2002). Authenticity of 2α-methylhopane, a likely biomarker of oxygenic photosynthesizers cyanobacteria, extracted from the 2.7Ga black shale (Brocks et al., 1999, Eigenbrode et al. 2008) has also been challenged (e.g., Brocks et al. 2011, Rasmussen et al. 2008). Therefore the timing of emergence for oxygenic photosynthesis remains unconstrained. It is important to determine if a “biomarker” in black shales is indigenous or contamination in later stages by a novel method. Here we report our development of analytical method for MALDI-TOFMS or imaging mass spectrometry (SHIMADZU iMScope at the Kochi Core Center, JAMSTEC) to perform in situ mapping of biomarkers in thin sections. Such location information is lost in a traditional method for biomarker extraction from rocks, because powdered, homogenized samples are used for extraction by organic solvents. For 2D analysis of biomarker distribution, the MALDI-TOFMS method has advantages over the traditional method. We could detect peak of m/z = 368.4, indicative of hopane, only to the areas where standard material of 2-methylhopane was applied before deposition as matrix of 2,5-dihydroxybenzoic acid. Then we show 2D, sedimentary-structure-dependent distributions of 2-methylhopane in thin sections made from drillcores (WRL1 and RHDH2A) of the black shales in the 2.7Ga Jeerinah Formation from Pilbara, Western Australia. These drillcores were previously used for detection of 2α-methylhopane by Brocks et al. (1999) and for geochemical and isotopic analyses by Yamaguchi (2002). We also used drillcores (ABDP#10) of the shallow-facies stromatolitic carbonates of the 2.7Ga Tumbiana Formation from the same district. We examined effects of artificial contaminations of oils into some representative rock types, to see how these contaminants survive against rigorous rinsing by water and organic solvents and were detected by MALDI-TOFMS. We dipped the rock specimens of the Archean black shale and the Cenozoic mudstone, basalt, and granite into high-viscosity olive oils and low-viscosity invasive lubricant (machine oils). We could detect peaks of m/z = 242.3 and 284.1 of oils, not only for the contaminated parts by the oils, irrespective of supersonic rinsing. Supersonication could not fully eliminate the oily contaminants. Sedimentary-structure-dependent distributions of 2-methylhopane in thin sections are the keys for authentic biomarker detection. We confirmed (1) syngenesity of hopane in the 2.7Ga black shales, suggesting operation of oxygenic photosynthesis in the 2.7Ga shallow ocean, but at the same time (2) unexpected survivability of biomarkers during supersonication of the samples. Biomarker mapping by MALDI-TOFMS proved to be a powerful tool for testing its syngenesity. Our results have important implications for the evolution of microbial biosphere and that of redox states in the atmosphere-ocean system in the early Earth. KE Yamaguchi(1*), H Saito(1), K Ishikawa(1), T Okumura(2), and A Ijiri(3) (1) Department of Chemistry, Toho University, Funabashi, Chiba 274-85110 (2) Centre for Advanced Marine Core Research, Kochi University, Nankoku 783-8502 (3) Faculty and Graduate School of Maritime Sciences, Kobe University, Kobe 658-0022