Full Citation: Kadoya, S., Krissansen?Totton, J., & Catling, D. C. (2020). Probable Cold And Alkaline Surface Environment Of The Hadean Earth Caused By Impact Ejecta Weathering. Geochemistry, Geophysics, Geosystems, 21 (1). https://doi.org/10.1029/2019gc008734.
Abstract: Constraining the surface environment of the early Earth is essential for understanding the origin and evolution of life. The release of cations from silicate weathering depends on climatic temperature and urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0001, and such cations sequester urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0002 into carbonate minerals in or on the seafloor, providing a stabilizing feedback on climate. Previous studies have suggested that this carbonate?silicate cycle can keep the early Earth’s surface temperature moderate by increasing urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0003 to compensate for the faint young Sun. However, the Hadean Earth experienced a high meteorite impactor flux, which produced ejecta that is easily weathered by carbonic acid. In this study, we estimated the histories of surface temperature and ocean pH during the Hadean and early Archean using a new model that includes the weathering of impact ejecta, empirically justified seafloor weathering, and ocean carbonate chemistry. We find that relatively low urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0004 and surface temperatures are probable during the Hadean, for example, at 4.3 Ga, urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0005 (in bar) is urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0006 urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0007 and temperature is urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0008 urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0009 K. Such a low urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0010 would result in a circumneutral to basic pH of seawater, for example, urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0011 urn:x-wiley:ggge:media:ggge22102:ggge22102-math-0012 at 4.3 Ga. A probably cold and alkaline marine environment is associated with a high impact flux. Hence, if there was an interval of an enhanced impact flux, that is, Late Heavy Bombardment, similar conditions may have existed in the early Archean. Therefore, if the origin of life occurred in the Hadean, life likely emerged in a cold global environment and probably spread into an alkaline ocean.
URL: https://doi.org/10.1029/2019GC008734