Did hydrothermal vents push the frontiers of habitability on the early Earth?

Nitrogen (N) and phosphorus (P) are essential nutrients to all life on Earth. Scarcity of these nutrients can limit biological productivity while unrestricted supplies can lead to bacterial blooms with severe environmental impacts. Investigating the N and P cycles is therefore critical for topics ranging from life's origins to modern environmental change. The aim of this research programme is therefore to (a) create a new analytical centre for N and P geochemistry, including experimental facilities, (b) apply these tools to investigate underexplored pathways of N and P cycling, and (c) incorporate bioinformatic data to reconstruct the biological utilisation of rare P species. The proposed project will represent the first set of applications of the new analytical facilities.

The major thrust of this project is the fundamental question how early life was sustained. Several lines of evidence suggest that primary productivity was severely suppressed throughout the Precambrian, because phosphate and nitrate - the two major forms of P and N in the modern ocean - were much less soluble in ancient oceans. We hypothesise that submarine volcanism, which sets off hydrothermal convection cells through oceanic crust, generated reduced forms of nitrogen and phosphorus and thus created important point sources of nutrients for early life. To test this hypothesis, we will develop a new hydrothermal reaction chamber that allows us to conduct experiments under elevated pressures and temperatures, reminiscent of deep-sea hydrothermal vents. Different gases (N2, CO2, CH4), fluids (saline, fresh), phosphate phases and catalytic minerals (magnetite, sulphides) will be added to the reactor under a range of conditions. The products will be analysed for nitrogen isotopic ratios (15N/14N) and phosphorus speciation.

The main objectives are:
* Measure the isotopic fractionation associated with abiotic hydrothermal N2 reduction to ammonium and organic amines. These results will allow us to re-visit the existing N isotopic record (including organic-rich sedimentary rocks and hydrothermally influenced strata) and determine if hydrothermal N sources played a significant role in Precambrian biogeochemical cycles.
* Quantify the yield of hydrothermal phosphate reduction to phosphite. Phosphite, a reduced form of P, is significantly more soluble than phosphate. Previous experiments have shown that phosphite can be produced from the reduction of simple phosphate salts. We will conduct new experiments with natural phosphate minerals to derive reaction efficiencies for hydrothermal scenarios. We will also measure how much phosphite is taken up into minerals to create a calibration for geochemical measurements of phosphate in the rock record.
* Reconstruct the radiation of phosphite-using enzymes across the tree of life. Phylogenetic data and molecular clocks will be used to infer the birth, loss and transfer of relevant genes. This analysis will reveal if phosphite utilisation did indeed scale with the extent of hydrothermal activity on early Earth, which would support our hypothesis of hydrothermal phosphite sources.
The results from this work will advance our understanding of how early life was sustained. If we can show that hydrothermal vents are significant sources of bioavailable phosphite and reduced nitrogen, this would have major implications for the habitability of other volcanically active planets. The analytical setup that will be developed and optimised under the umbrella of this project would open up further possibilities for future studies of ancient and modern nutrient cycling. For example, the experimental setup will allow investigating the behaviour of critical metals under hydrothermal conditions, and the analytical suite will create new opportunities to study N and P cycling in modern polluted settings. The facilities would thus create a new analytical centre in the UK and place the PI at the frontier of biogeochemical research.