Mass extinction of life at the end of the Permian ca. 250 million years ago was characterized by (1) abrupt and coincident extinctions in the ocean and on land during a period of only 10,000 years and (2) delay of ecosystem recovery during the following 10 million years encompassing the largest known turnover of marine and land biota. Previously suggested direct causes of this major event include gradual extreme warming, oceanic anoxia, a decrease in ozone by mass release of H₂S and CH₄, and gradual atmospheric hypoxia. A positive anomaly in the ³⁴S/³²S ratio of carbonate-associated sulfate (CAS) in uppermost Permian marine sediments implies that H₂S accumulated in the ocean during a period of 〜1 million years. The accumulation period was followed by massive release of H₂S (evidenced by a decrease in the ³⁴S/³²S ratio of CAS) coinciding with the mass extinction. Oxidation of the H₂S would have caused a significant decrease in atmospheric O₂. The hypoxia event occurred over a much shorter time period (10⁴ years) than previously suggested (10⁷ years) and can explain the rapidity of the major end-Permian mass extinction which triggered development of the Earth's modern biota.

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Organic geochemical records for devastation of terrestrial ecosystem in the environmental disturbance events of Permian-Triassic boundary (PTB) are reviewed. Paleontological and geological (sedimentological) investigations for terrestrial ecosystem and environment in PTB have provided information for collapse and devastation of ecosystem in the supercontinent (Pangea), such as dieback of woody vegetation, massive loss of rooted plant, repopulation of herbaceous lycopsid, proliferation of fungal remain, cease of peat formation, and increased mutagenesis of spore and pollen. Recent studies of biomarker and kerogen reported that remarkable abundances of aromatic furans in marine sedimentary sequence of PTB showed organic geochemical evidence of massive soil erosion due to destruction of terrestrial vegetation. Sedimentary aromatic furan is possibly derived from polysaccharide in soil, whereas aromatic furan is also known to be synthesized as secondary metabolite of extant lichen. Thus, source(s) of sedimentary aromatic furan is still controversial, and further examination is necessary.

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Oceanic Anoxic Events (OAEs) occurred several times during the mid-Cretaceous. The black shales that have laminated structure and contain abundantly organic carbon were deposited during the OAEs. OAEs were related to drastic environmental changes and turnovers of marine biota, which were reconstructed by organic geochemical investigations such as the biomarker analyses. OAE1a (early Aptian) was characterized by high contribution of cyanobacteria as a marine producer to sedimentary organic matter revealed by analyses of 2-methylhopanoids. In OAE1a, the high productivity of eukaryote in surface ocean was also considered from high concentrations of steroid hydrocarbons, and other specific biomarkers such as alkenone and dinosterane were identified. On the other hand, OAE1b (late Aptian〜early Albian) was characterized by high contribution of archaea such as methanogen as a marine producers to sedimentary organic matter up to 80% revealed by the high concentrations of archaea-derived isoprenoids. Moreover, high concentrations of terrestrial biomarkers such as dibenzofuran and retene were recognized during OAE1b. This fact indicates that a large amount of terrigenous matter was more efficiently transported to ocean during OAE1b.

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Mass extinction event at the Cretaceous-Paleogene (K-P) boundary (65.5Ma) is characterized by the simultaneous disruption in global carbon cycling. Multiple stable carbon isotope profiles in both marine and terrestrial sedimentary sequences have revealed detailed recovery patterns from the perturbations of marine and ocean surface-atmosphere carbon reservoirs. Recent studies suggest a close linkage between carbon cycle recovery and ecosystem diversification in the ocean; but the roles of the exogenic carbon cycle on the terrestrial environment and ecosystem still remain unclear. The leaf wax n-alkanes in the K-P boundary sequence exhibit variations in their molecular distribution and/or isotopic composition associated with the climatic changes, and thus, are a useful proxy for accessing paleoterrestrial environment and also a key of revealing its relation to the carbon cycle perturbation at that time.

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The Paleocene-Eocene thermal maximum (PETM) is marked by a large negative carbon isotope excursion (CIE) and massive seafloor carbonate dissolution. Both phenomena are thought to have been caused by a sudden release of a large mass of carbon. The step-like nature of the CIE onset combined with the CIE magnitude has been explained by multiple dissociation of methane clathrate as the primary source of carbon. The natures of onset and the magnitude of CIE, however, are different between marine and terrestrial records implying potential artifacts in either or both records. Recently, the carbon isotope stratigraphy based on various techniques including compound-specific isotope analysis on terrestrial and marine biomarkers, single specimen analysis on surface-dwelling planktonic foraminifera revealed that 'actual' CIE is as large as 4‰ or larger, and the onset of the CIE was geologically instantaneous. These results demonstrated that the CIE magnitude (2-3‰) previously applied to estimate the mass of carbon released during the PETM was considerably underestimated and that abrupt input of ¹³C-depleted carbon to the ocean-atmosphere system. Forthcoming high-resolution studies on the PETM with precise inter-regional correlation would provide a unique opportunity for comparative research of global warming between PETM period and the present.

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I review the organic geochemical studies of lake waters and sediments, soils, Beacon Supergroup of Gondowanaland sediments and cryptoendolithic microbial communities of the McMurdo Dry Valleys in southern Victoria Land, Antarctica. Total organic carbon contents in the anoxic lake waters of meromictic lakes are extremely high due to the accumulation of refractory organic matter from microbial degradation together with dissolved salts. Vertical distribution of physicochemical properties reveals the zonation of microbial communities in the lakes. The composition of organic components in the lakes and ponds varies largely, reflecting differences in microbial communities and their activities. Significant amount of long-chain (>C₁₉)n-alkanes and n-alkanoic acids are detected in some lake and pond sediments, implying that microorganisms are important sources of their long-chain components in natural environments on the earth. Unusually, the predominant sterol in the McMurdo Dry Valleys is frequently 24-ethylcholest-5-en-3β-ol (C₂₉ cholesterol) which is synthesized by green algae, cyanobacteria and/or diatoms. As expected a series of phenolcarboxylic acids related to the lignin of vascular plants are absent but p-hydroxybenzoic acid is predominant phenolcarboxylic acids in the lakes and soils.
The occurrence of matured isomers of steranes and triterpanes, the paucity of n-alkenoic acids and visual kerogen in soil samples from the McMurdo Dry Valleys suggest that organic components in the soil samples are derived from erosion of Beacon Supergroup sedimentary rocks and past biological debris containing vascular plant waxes as well as wind transported cyanobacterial mats rather than living organisms.
Long-chain n-alkanes and n-alkanoic acids are found in Beacon Supergroup samples from the McMurdo Dry Valleys. Steranes, triterpanes and visual kerogen results of Beacon Supergroup samples from Allan Hills imply that organic materials in the sedimentary environments are contributed mainly by vascular plants with some influence of microorganisms, whereas those of Carapace Nunatak sample are largely due to fern spores. Variable thermal maturities of steranes probably reflect thermal effects of basaltic dikes on the Beacon Supergroup in these areas in Jurassic time. Thermal stresses of the formation of the Beacon Supergroup prior to basaltic intrusion have been estimated to be quite low.
Long-chain anteiso-alkanes and anteiso-alkanoic acids are often major components in cryptoendolithic microbial communities originating probably from microorganisms, such as bacteria and lichens in moderate pH conditions (pH 3-5). Normal alkenoic/alkanoic acid ratios are probably useful marker for the fossilization of cryptoendolithic microbial communities. Thermally matured triterpanes and steranes from fossilized associations on Mount Fleming strongly suggest the presence of Gondowanaland sediments formed during Devonian and Jurassic (400-180 million years ago).

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Organic compounds in chondritic meteorites are the products of a complex history that began in dense molecular clouds and the diffuse interstellar medium. This primordial materials were subsequently modified during the formation of the protoplanetary disk, and during the formation and alteration of the meteorite parent bodies. Insoluble organic matter is a complex and heterogeneous macromolecular material that accounts for a major portion of the organic carbon in chondrites. Recent analyses of the insoluble organic matter from a range of chondrites spanning the major groups (CM, CI, CR, CV, CO, ungrouped C2, ordinary, enstatite) and petrologic types 1-3+ have revealed that the organic matter clearly records the history of chemical processing on the meteorite parent bodies. This review first introduces the chemical characteristics of the insoluble organic matter from the well-studied CM2 chondrites, and then highlights the molecular and isotopic variations of the insoluble organic matter in different meteorite groups which could be indicators of aqueous alteration and/or thermal metamorphism on the meteorite parent bodies.

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One of the most powerful techniques in the molecular isotope studies is compound-specific isotope analysis (CSIA) by gas chromatograph/isotope ratio mass spectrometer (GC/IRMS), which allows a rapid and precise determination of stable carbon, nitrogen, and hydrogen (and oxygen) isotopic compositions of individual compounds even in complex mixture of components. After commercial production of GC/IRMS in the 1990s, CSIA has explosively been used for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and for reconstructing paleoenvironments. However, it is also true that fundamental analytical parameters of GC/IRMS has not been known extensively, which often leads to unreliable determination of the isotopic compositions. Unfortunately, based on such unreliable determination, several studies have unconsciously reported essentially inaccurate data and associated discussion. Therefore, in this paper, we review a brief outline of GC/IRMS and associated methodologies, and summarize the instrumental factors influencing accuracy and precision of the isotope measurements. We hope that this paper is useful for applying CSIA to future studies.

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Many halophilic archaea produce a characteristic C₂₅-C₂₀ isoprenoidal diether as a lipid-core portion of their body. This compound has a possibility for the biomarker to indicate a hypersaline environment. However, there have been a few experiments were performed for this compound in natural samples. In the present study, analytical methods of isoprenoidal lipid-core produced by an "ordinal" halophilic archaea Natrinema pallidum were established by ESI-MS and GC-MS. Furthermore, the compositional change for the C₂₅-C₂₀ diether and C₂₀-C₂₀ diether (archaeol), which simultaneously produced by the microorganism, was investigated. In higher temperature and higher salt concentration, C₂₅-C₂₀ diether tends to produce more than lower temperature and concentration. This may be adaptation to extreme environment of this microorganism.

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