CAREER: Understanding biosphere-geosphere coevolution through carbonate-associated phosphate, community archives, and open-access education in rural schools

Phosphorus is an essential nutrient for life. Today, phosphorus exists in extremely low abundance in the oceans limiting the productivity of the biosphere. The majority of phosphorus is derived from weathering of phosphate minerals from continents. However, for the first one to two billion years of Earth history, there were no continents to weather. Shortly after the first continents emerged above sea level (~3.2 to 2.6 billion years ago, Ga), microbes evolved the ability to perform oxygenic photosynthesis, which led to an oxygen-rich atmosphere and massive increase in primary productivity. Was the oxygenation of the oceans and atmosphere directly related to weathering of Earth’s first continents? This study will develop a record of the concentration of phosphorus in ancient oceans ~2 to 0.5 Ga to examine if the evolution of marine microorganisms was linked to weathering of early continents when the Earth was covered in ice. Ultimately, phosphorus abundance may have enabled the evolution of aerobic and multicellular organisms. The research will be integrated into new Earth sciences curricula developed with local high school teachers for neighboring rural districts. The project will develop open-access classroom and field-based learning modules and virtual field trips that connect students to the Cambrian explosion—the evolution of macroscopic animals—in the Pennsylvania landscape. The efficacy of the new curricula will be assessed through serial knowledge assessments implemented before and after exposure and “knowledge boosts” in subsequent years. Mid-Atlantic high school teachers will be trained in various resources to be implemented in their classrooms.Microbes have been intimately linked to carbonate minerals and the chemical evolution of Earth’s surface since life began. The metabolic innovation of oxygenic phototrophy >2 billion years ago contributed to the rise of oxygen, increased global primary productivity, and permanently changed biogeochemical cycles. However, little is known about why microbes evolved the ability to photosynthesize relatively late in the history of life, and what controlled the pace of subsequent microbial evolution. The primary goal of this CAREER award is an assessment of phosphate availability—an essential nutrient for all life—in the environments that host textural and geochemical evidence for primitive microbes and emergent metabolisms. Was the reduced productivity of the Mesoproterozoic a symptom of a phosphate reservoir depleted by oxygenic phototrophs? Was the evolution of crown group eukaryotes and metazoans fertilized by weathering-derived phosphate from Neoproterozoic global glaciations and the breakup of supercontinents? This project tests the hypothesis that enhanced phosphate availability was essential to the evolution of eukaryotes and metazoans by reconstructing seawater [P] via carbonate-associated phosphate (CAP) on existing Precambrian sample sets within the context of Proterozoic global glaciations, tectonics, and existing temporal and diagenetic frameworks. The research will improve our understanding of CAP and its utility for geo- and astrobiology by (1) analyzing CAP in the same Precambrian samples that have a wealth of existing diagenetic and geochemical data, and (2) performing growth experiments to develop mineral-specific CAP-[P]seawater calibrations.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.