Life on an oxidizing planet: Microbial ecosystems of a Neoarchean carbonate platform

地球上生命的故事很大程度上是微生物和微生物生态系统的故事。微生物是地球上最早的生命，它们仍然是最丰富的生命形式，人们越来越清楚地认识到，没有它们，任何复杂的生命形式都无法生存。然而，尽管微生物的重要性是不可否认的，但它们的早期进化历史并没有得到很好的理解。大约24到23亿年前，微生物通过向大气中添加氧气而深刻地改变了这个星球。我们不知道这种氧化作用是如何发生的，也不知道它是如何影响地球上的生命的，但我们知道它最终为包括所有动物、植物和真菌在内的多细胞生命的进化铺平了道路。该项目将研究生活在25亿年前的微生物生态系统化石，不仅将扩大我们对地球上生命早期进化的认识，还将有助于寻找其他星球上的生命。国际合作、学生培训和教育推广活动将是该项目的重要组成部分。该项目将研究的微生物生态系统保存在南非Campbellrand-Malmani碳酸盐岩台地（CMCP）。CMCP形成于27亿到25亿年前，历时2亿年。项目团队将分析存在于CMCP的多种微生物生态系统，并对新太古代海洋生态系统进行整体分析，并对地球与生命共同进化的关键时期提供重要细节。这将通过描述保存下来的微化石，使用稳定碳同位素分析来约束微生物化石在生命中可能使用的代谢途径，计算观察到的微化石组合的多样性和不同微生物岩中观察到的CMCP微化石组合的相似性，以及评估初步观察到的新太古代生物矿化证据来实现。该项目将使用多种显微和光谱技术，包括透射光显微镜、二次电子显微镜、透射电子显微镜、共聚焦激光扫描显微镜、拉曼光谱、能量色散x射线光谱、同位素比质谱和二次离子质谱。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The story of life on Earth is largely the story of microbes and microbial ecosystems. Microbes were the first life on Earth, they are still the most abundant form of life, and it is becoming increasingly well understood that no complex life forms could survive without them. However, though the importance of microbes is undeniable, their early evolutionary history is not well understood. About 2.4 to 2.3 billion years ago, microbes changed this planet in a profound way by adding oxygen to the atmosphere. We do not know exactly how this oxygenation took place or how it impacted life on Earth, but we do know it ultimately paved the way for the evolution of multicellular life including all animals, plants, and fungi. This project will study fossilized microbial ecosystems that lived 2.5 billion years ago and will not only expand our knowledge about the early evolution of life on Earth, it will aid in the search for life on other planets. International collaboration, student training and educational outreach activities will be important components of the project. The microbial ecosystems that will be studied in this project are preserved across the Campbellrand-Malmani carbonate platform (CMCP) in South Africa. The CMCP formed over a 200 million year period, between 2.7 and 2.5 billion years ago. The project team will analyze the diverse microbial ecosystems that existed across the CMCP and produce a holistic view of a Neoarchean marine ecosystem and important details about a pivotal period in the coevolution of Earth and life. This will be accomplished by describing the preserved microfossils, using stable carbon isotope analysis to constrain the possible metabolic pathways the fossilized microorganisms used in life, calculating the diversity of observed microfossil assemblages and the similarity of CMCP microfossil assemblages observed in different microbialites, and evaluating evidence of Neoarchean biomineralization seen during preliminary observation. This project will use multiple microscopic and spectroscopic techniques, including transmitted light microscopy, secondary electron microscopy, transmission electron microscopy, confocal laser scanning microscopy, Raman spectroscopy, energy dispersive x-ray spectroscopy, isotope ratio mass spectrometry, and secondary ion mass spectrometry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.