|Title||Mantle cooling causes more reducing volcanic gases and gradual reduction of the atmosphere|
|Publication Type||Journal Article|
|Year of Publication||2020|
|Authors||Kadoya S., Catling D.C, Nicklas R.W, Puchtel I.S, Anbar A.D|
|Type of Article||Article|
|Keywords||Geochemistry & Geophysics; mass-independent fractionation; oxidation-state; redox; rise; sulfur; temperature; vanadium|
The early atmosphere contained negligible O-2 until the Great Oxidation Event (GOE) around 2.4 Ga, but evidence suggests that production of photosynthetic O-2 began hundreds of millions of years earlier. Thus, an ongoing debate concerns the trigger of the GOE. One possibility is that volcanic gases became more oxidising over time. Secular cooling of the mantle affects thermodynamic equilibria and also changes the proportions of reduced and oxidised volcanic gases. Here, we examine the consequences of mantle cooling for the evolution of Earth's atmospheric redox state. Contrary to some previous hypotheses, we show that as the mantle cools, volcanic emissions contain a greater proportion of reducing gases, which produces a more reducing atmosphere. However, the atmosphere became more oxic. Therefore, the redox consequences of other processes, such as secular oxidation of the mantle and/or hydrogen escape to space, must have dominated over that of mantle cooling in shaping the redox evolution of Earth's atmosphere.