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Global warming, the most severe faunal mass extinction and the shift of biogeochemical cycles were observed in the ocean across the Permian-Triassic boundary about 252 million years ago, providing an analog to understanding the modern oceans. Along with the progressive global warming, the biogeochemical cycle was documented to show a shift from the decoupled processes of carbon, nitrogen and sulfur prior to the mass extinction to the coupled biogeochemical processes during faunal mass extinction. The coupled biogeochemical cycle was further observed to shift from the coupled C-N processes during the first episode of the faunal mass extinction to the coupled C-N-S processes during the second episode, diagnostic of the progressive development of more deteriorated marine environmental conditions and the more severe biotic crisis across the Permian-Triassic boundary. The biogeochemical cycles could thus be an indication to the progressive collapse of marine ecosystems triggered by the global warming in Earth history. In modern oceans, the coupled C-N cycle triggered by the global warming was observed in some regions. If these local C-N processes develop and expand to the global oceans, the coupled C-N-S processes might be brought into existence and the marine ecosystems are inevitable to suffer from complete collapse as observed at 252 million years ago. [ABSTRACT FROM AUTHOR]

Microbes not only show sensitive responses to environmental changes but also play important roles in geochemical and geophysical systems. It is well known that microbes have caused major changes in surface environments and biogeochemical cycles through Earth history. Microbial processes can also induce the synthesis of certain minerals under Earth-surface conditions that previously were believed to form only under high temperatures and pressures in the deep Earth. For example, microbes can promote the conversion of smectite to illite, synthesis of authigenic plagioclase, precipitation of dolomite, and biotransformation of geolipids. These effects of microbes are due to their large surface/volume ratios, enzyme production, and abundant functional groups. Microbial catalyzation of chemical reactions proceeds through reaction-specific enzymes, a decrease in Gibbs's free energy, and/or break through the dynamics reaction thresholds via their metabolisms and physiology. Microbes can lower the surface free energy of mineral nuclei via biophysical adsorption due to their large surface/volume ratios and abundant functional groups. The mineral precipitation and transformation processes induced by microbes are functionally equivalent to geological processes operating at high temperatures and pressures in the deep Earth, suggesting that microbial processes can serve as analogs to deep abiotic processes that are difficult to observe. [ABSTRACT FROM AUTHOR]

Geobiology is a new discipline on the crossing interface between earth science and life science, and aims to understand the interaction and co-evolution between organisms and environments. On the basis of the latest international achievements, the new data presented in the Beijing geobiology forum sponsored by Chinese Academy of Sciences in 2013, and the papers in this special issue, here we present an overview of the progress and perspectives on three important frontiers, including geobiology of the critical periods in Earth history, geomicrobes and their responses and feedbacks to global environmental changes, and geobiology in extreme environments. Knowledge is greatly improved about the close relationship of some significant biotic events such as origin, radiation, extinction, and recovery of organisms with the deep Earth processes and the resultant environmental processes among oceans, land, and atmosphere in the critical periods, although the specific dynamics of the co-evolution between ancient life and paleoenvironments is still largely unknown. A variety of geomicrobial functional groups were found to respond sensitively to paleoenvironmental changes, which enable the establishment of proxies for paleoenvironmental reconstruction, and to play active roles on the Earth environmental changes via elemental biogeochemical cycles and mineral bio-transformations, but to be deciphered are the mechanisms of these functional groups that change paleoenvironmental conditions. Microbes of potential geobiology significance were found and isolated from some extreme environments with their biological properties partly understood, but little is known about their geobiological functions to change Earth environments. The biotic processes to alter or modify the environments are thus proposed to be the very issue geobiology aims to decipher in the future. Geobiology will greatly extend the temporal and spatial scope of biotic research on Earth and beyond. It has great potential of application in the domains of resource exploration and global change. To achieve these aims needs coordinative multidisciplinary studies concerning geomicrobiology and related themes, database and modeling of biogeochemical cycles, typical geological environments, and coupling of biological, physical, and chemical processes. [ABSTRACT FROM AUTHOR]

Microbes are well-known for their great diversity and abundance in modern natural environments. They also are believed to provide critical links among higher organisms and their associated environments. However, the low diversity of morphological features and structures of ancient microbes preserved in sediments and rocks make them difficult to identify and classify. This difficulty greatly hinders the investigation of geomicrobes throughout Earth history. Thus, most previous paleontological studies have focused on faunal and floral fossils. Here, geomicrobial functional groups (GFGs), or a collection of microbes featured in specific ecological, physiological or biogeochemical functions, are suggested to provide a way to overcome the difficulties of ancient microbe investigations. GFGs are known for their great diversity in ecological, physiological and biogeochemical functions. In addition, GFGs may be preserved as the biogeochemical, mineralogical and sedimentological records in sediments and rocks. We reviewed the functions, origins and identification diagnostics of some important GFGs involved in the elemental cycles of carbon, sulfur, nitrogen and iron. GFGs were further discussed with respect to their significant impacts on paleoclimate, sulfur chemistry of ancient seawater, nutritional status of geological environments, and the deposition of Precambrian banded iron formations. [ABSTRACT FROM AUTHOR]

Evaluating the pre-Jurassic marine source rocks in China has been difficult because these rocks are generally too high- or over-maturated for most traditional methods to work. As to the remaining parameter TOC (%), its lower limit for recognizing the carbonate source rocks in China has been in dispute. Nineteen Phanerozoic sections in the Middle-Upper Yangtze Platform and the Guizhou-Hunan-Guangxi Basin have been studied in search for a different approach to complementing the traditional evaluation method for these source rocks. We have applied a geobiological approach to tracing the organic carbon (OC) output and accumulation from the living stage (primary productivity) to the post-mortem deposited remains, and finally to the preserved burial organics. Four biological and geological parameters are employed to represent the OC of the three stages. A series of proxies of these parameters are discussed and integrated to establish a geobiological evaluation system independent of TOC and other traditional methods. Here we use the Guangyuan section in Sichuan as an example for the geobiological evaluation. Our results indicate that in the argillaceous rocks, the geobiological parameters show the qualified source rocks in accordance with high TOC values; but in the carbonates, the good source rocks delineated by the geobiological parameters have a wide range of TOC, from 0.03% to 1.59%, mostly <0.3%. We suggest that it is still premature to set TOC=0.3% or 0.5% as the lower limit for the pre-Jurassic carbonate source rocks in South China. [ABSTRACT FROM AUTHOR]

The article explores the use of the geobiological approach in the assessment of Chinese carbonate source rocks. A series of paleoecological and biogeochemical parameters were employed to represented organic carbon (OC). It notes that clastic rocks based on geobiological parameters are qualified source rocks, while good source rocks from carbonates have low total organic carbon (TOC) values. It also notes the broad range of habitat types for carbonate source rocks in the Yangtze platform.

Geomicrobiology is a sub-discipline of geobiology and emphasizes the interaction between microorganisms and their environment on Earth. There is a need to explicitly emphasize the biogeochemical processes performed by microorganisms associated with Earth’s tectonic activities, especially under the framework of the modern theory of plate tectonics. Tectonomicrobiology aims to create a better synergy between microbial and active tectonic processes. This explicit synergy should also foster better communications between solid Earth scientists and life scientists in terms of holistic Earth system dynamics at both tectonic and micro-scales. [ABSTRACT FROM AUTHOR]