CAREER: An Evolutionary Framework for the Molecular Fossil Record

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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.