Abstract:

Phosphorus (P) is a critical nutrient for all life as we know it and may have shaped the evolution of the biosphere over the past 4 billion years. However, the availability of P on the early Earth is poorly constrained, with estimates of marine phosphate concentrations ranging over five orders of magnitude. A mostly neglected variable in the ancient P cycle is the prevalence of reduced P, in particular phosphite. Incorporating reduced P into existing models may help resolve some of the uncertainties. Here, I will present new data about possible sources and sinks of reduced P on the Archean Earth.
 
Experimental work allows us to place new constraints on metamorphic phosphite formation, while data from the rock record show that phosphite was released from magmatic rocks and during impact events. However, these sources may have been relatively low in comparison to biological phosphite production, which probably began around the time of the Great Oxidation Event as indicated by phylogenetic reconstructions of enzyme evolution. We speculate that this biological source flux was initiated in response to a declining phosphate reservoir, caused by increasing biological productivity and perhaps more extensive precipitation of iron oxides that efficiently scavenged phosphate from the water column.
 
In conclusion, reduced P is significantly more soluble than phosphate and more widespread in natural environments than previously thought. Given its bioavailability and reactivity towards organic matter, it should be considered as a variable in assessing the habitability of other worlds.

Speaker: Dr. Eva Stueeken (University of St. Andrews)

Host: Yasuhito Sekine, ELSI.

Date: Wed. 30 Apr. 16:00-17:00 JST

Venue: Online