Nitrate availability and the rise of eukaryotic algae

Limited N supply to phytoplankton has been proposed as a throttle on the evolution of eukaryotes, as well as on regulation of planetary climate. To test these hypotheses, we analyze the N isotopic composition of organic matter in ancient marine sediments. To-date, this has taught us that fixed N was likely bioavailable well before the rise of eukaryotes, but spatially restricted in Earth's middle ages. On an even broader scale, we've used Earth system modeling to show that changes in atmospheric N2 levels can arise from biological activity & that the co-existence of N2 + O2 is a strong atmospheric biosignature. More recently we've been coupling N isotopes to lipid biomarker data (with Jochen Brocks) to more precisely discern the role of N availability in the emergence of eukaryotic ecosystems.