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Physical Chemistry

Plate Tectonics And The Air We Breathe

Geological collision chemistry is identified as a source of Earth’s atmospheric nitrogen

by Jyllian Kemsley
October 27, 2014 | A version of this story appeared in Volume 92, Issue 43

Geological movements of Earth’s crust have contributed to the planet’s nitrogen-rich atmosphere, according to research carried out at the Carnegie Institution of Washington (Nat. Geosci. 2014, DOI: 10.1038/ngeo2271). In areas where crustal plates collide and one plate subducts under the other, the subducting plate carries with it water and other materials that help create an oxidizing environment in the molten mantle beneath the overlying plate. The oxidizing environment favors formation of N2 in the mantle, compared with NH4+ in other areas, according to thermodynamic calculations done by Sami Mikhail, now at Bristol University, in England, and Dimitri A. Sverjensky of Johns Hopkins University. The N2 then degases to the atmosphere through volcanic emissions. The processes likely enriched Earth’s atmosphere in N2 starting in the early Archean period, about 3.5 billion years ago. “Plate tectonics has literally changed the air life breathes,” Mikhail says. In contrast to Earth, Mars and Venus lack plate tectonics and their atmospheres contain far less N2.

Diagram of different types of volcanos and the amount of atmospheric nitrogen they yield.
Credit: Sami Mikhail


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