Abstract: 
Phosphorus (P) is the key bionutrient thought to limit primary productivity on geological timescales. The sedimentary record suggests low availability of phosphate in Archean oceans, but quantification of the P cycle and how it changed through a billion years of recorded Archean history remain a challenge, hindering our understanding of the role played by P in biosphere/geosphere co-evolution on the early Earth. In this talk, I will present our recent studies on quantitatively assessing key processes of the P cycle – continental weathering, seafloor weathering, and ocean recycling – by considering the emergence and elevation of continents and the evolution of climate, atmosphere, and ocean chemistry during the Archean Eon. Our models show an increasing continental flux of bioavailable P through time, reaching levels comparable to modern values by the end of the Archean Eon. However, precipitation of Fe(II)-phosphate (vivianite) might have resulted in low levels of seawater P. Optimistic assumptions about the recycling efficiency of P on the Archean Earth lead us to estimate that by the end of the eon the total flux of P (continental weathering + recycling) could have supported NPP at levels up to 7 % of the modern. The total flux of P would have been much lower on the early and middle Archean Earth, whereas fluxes of electron donors could have been higher, suggesting very low productivity and P-limitation of marine ecosystems during much of the eon. Once oxygenic photosynthesis reached ecological significance, probably near the end of the Archean, our estimated flux of P would allow rapid oxidation of atmosphere.

Speaker: Dr. Jihua Hao, Rutgers University

Speaker bio: 
Jihua Hao is current working as a postdoctoral researcher at Rutgers University with Profs. Nathan Yee and Paul Falkowksi. He got PhD degree in Geochemistry from Johns Hopkins University in 2016. He is interested in early Earth geochemistry, high temperature-pressure geochemistry, origin of life, astrochemistry and astrobiology.

Host: Yamei Li, ELSI

Date: Fri, 3 Jul 2020 at 10:30 JST (Fri, 3 Jul 2020 at 01:30 UTC)

Venue: Online