Investigating the formation of biogenic magnetite and the preservation of magnetofossils: implications for biosignatures and paleoenvironments

使用跨学科的方法，集成矿物学，生物地球化学和微生物学和电子显微镜的应用，我研究导致生物矿物形成的过程，并表征它们的化学和同位素组成，晶体形态和矿物结构。总的来说，通过了解生物矿化的过程和途径，我们对生物在地球化学循环中的作用有了有价值的认识。生物矿物作为生命史和环境信息的档案，可以作为古代地球和地外地质系统的生物标志，用于了解生命和生物圈的起源和演化，为重建古环境和古气候提供信息。我目前的研究方向是研究由细菌产生的磁铁矿晶体，以提高矿物学和地球化学标准，以区分生物成因和非生物成因的磁铁矿。通过(1)分析古新世-始新世极热期（PETM）沉积物中新发现的巨型生物成因磁铁矿及其与海绿石等其他铁矿物的关系；(2)研究淡水湖和海洋生境中培养的趋磁细菌和磁性细菌及其磁铁矿化石（即磁化石）的磁小体结构细节。由于始新世第三纪始新世第三纪是一个极端的全球变暖事件，在大约55.5 Ma时，温度在180 ky的间隔内升高了约5 ~ 9°C，对始新世第三纪生物成因磁铁矿的研究可能为该时期的古环境条件提供新的线索。它还暗示了在“人类世”（当今的全球时间）期间，人为造成的全球变暖可能带来的后果，因为新千年新世（PETM）是当今的理想类比。

Using an interdisciplinary approach that integrates mineralogy, biogeochemistry and microbiology and the application of electron microscopy, I investigate processes that lead to the formation of biominerals and characterize their chemical and isotopic composition, crystal morphology and mineral structure. In general, by understanding the processes and pathways of biomineralization, we gain valuable insight into the role of biology in geochemical cycles. Biominerals as archives of life history and environmental information can be used (i) as biosignatures in ancient terrestrial and extraterrestrial geological systems, (ii) to understand the origin and evolution of life and the biosphere, and (iii) to provide information for reconstructing paleoenvironments and paleoclimates. My current research program is directed towards investigating magnetite crystals produced by bacteria in order to improve the mineralogical and geochemical criteria to distinguish between biogenic and non-biogenic magnetite. This is accomplished by (1) analyzing the newly discovered giant biogenic magnetite present within sediments of the Paleocene-Eocene Thermal Maximum (PETM) and their relationship to other Fe minerals such as glauconite, and (2) studying the structural details of magnetosomes from both cultured magnetotactic bacteria and magnetic bacteria collected from freshwater lakes and marine habitats as well as their magnetite fossils (i.e., magnetofossils). As the PETM is characterized as an extreme global warming event where temperatures increased by about 5 to 9°C over an interval of 180 ky at about 55.5 Ma, investigation of the biogenic magnetite in the PETM may shed new light on the paleoenvironmental conditions of this period. It also has implications for the possible consequences of man-made global warming during the "Anthropocene" (the present age of global time) as the PETM is an ideal analogue for the present.