CAREER: An Evolutionary Framework for the Molecular Fossil Record

生物产生非生物物质无法产生的化合物。其中一些化合物被保存在岩石中，为过去生活的生物体提供了“生物特征”。对这些生物特征的研究对于自然资源勘探、识别污染源、重建地球上生命的历史，甚至在火星上寻找生命的迹象都是有价值的。虽然科学家们非常擅长识别岩石中含有的生物特征，但在确定每种化合物是由哪种生物产生的问题上，存在很多分歧。这个项目使用最新的遗传学工具来确定哪些生物体拥有制造各种生物特征所必需的基因，以及它们的祖先在过去什么时候获得了这种能力。该项目的外联部分包括开发课程，培训年轻地质学家在自己的研究中使用这些遗传工具，以及为美国印第安学者提供指导计划。该项目侧重于甾烷，一种由真核生物细胞膜中发现的固醇产生的地球化学生物标志。该项目结合了比较基因组学和分子钟分析，以确定甾醇生物合成所需的基因何时进化，以及哪些群体在地质时期拥有相关基因。这些工具将被用来重新评估最近在甾烷研究中备受瞩目的研究，包括5.6亿年前的狄更森水母化石是否代表一种早期动物，6.3亿年前的24异丙基胆甾烷是否为第一批海海绵提供了生物标志物，以及16亿年前的不寻常甾烷是否来自真核生物或细菌来源。更广泛的影响包括为年轻地球科学家开设的计算系统发育短期课程，该课程将在加州理工学院的国际地球生物学课程每年教授一次。另一个项目针对加州莱克县附近的美国印第安社区大学学生。通过建立联系，我们将招募有前途的学生在加州大学戴维斯分校博德加海洋实验室进行夏季研究和专业化。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。

Living things produce chemical compounds that cannot be produced from non-living matter. Some of these compounds get preserved in rocks and provide “biosignatures” for organisms that lived in the past. The study of these biosignatures is valuable for natural resource exploration, identifying sources of pollution, reconstructing the history of life on Earth, and even when looking for signs of life on Mars. While scientists are very good at identifying the biosignatures contained in rocks, there is a lot of disagreement when it comes to determining what sort of organism made each compound. This project uses the latest tools in genetics to identify what living organisms have the genes necessary to make various biosignatures, and when in the past their ancestors gained that ability. Outreach components of this project involve developing courses to train young geologists to use these genetic tools for their own research, as well as a mentoring program for American Indian scholars.This project focuses on steranes, a geochemical biosignature produced from the sterols found in the cell membranes of eukaryotes. This project combines comparative genomics and molecular clock analyses to determine when the genes required for sterol biosynthesis evolved, and which groups had the relevant genes through geologic time. These tools will be leveraged to reevaluate recent high-profile studies in sterane research, including whether the ~560 million-year-old fossil Dickinsonia represents an early animal, whether ~630 million-year-old 24-isopropylcholestanes provide a biomarker for the first sea sponges, and whether unusual ~1.6 billion-year-old steranes came from eukaryote or bacterial sources. Broader impacts include a short course in computational phylogenetics for young geoscientists, which will be taught annually at Caltech’s International Geobiology Course. An additional program targets American Indian community college students around Lake County, California. Through established connections we will recruit promising students for summer research and professionalization at the UC Davis Bodega Marine Laboratory.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.