Big Ideas in Volcanology #08:


#08.2 _ Volcanism contributed to the formation of a secondary atmosphere and oceans

Study of zircons has found that liquid water must have existed as long ago as 4.4 Ga, soon after the formation of the Earth. This requires the presence of an atmosphere, probably formed at first by the steam escaped from the crust and other gases due to severe volcanism and similar to those emitted by volcanoes at the present day (e.g. water vapor, SO2, CO2), plus NH3 (ammonia) and CH4 (methane).

Example of gases emitted by volcanoes

A cooling phase covers the period from about 4.4 to 4.0 Ga, when heat from radioactivity and gravitational accumulation started to decrease.

The rock vapor condensed leaving behind hot volatiles which probably resulted in a heavy CO2 atmosphere with H2 and water vapor. As the planet cooled, clouds formed and a heavy rainfall created the oceans. These may have begun forming by 4.2 Ga or as early as 4.4 Ga, but a major part of CO2 exhalations were soon dissolved in water and built up carbonate sediments. Liquid water oceans existed despite a surface temperature of about 230 °C because of the pressure of the heavy CO2 atmosphere. As cooling continued, subduction and dissolving in ocean water removed most CO2 from the atmosphere but levels oscillated as new surface and mantle cycles appeared.

Pillow basalts and deep marine sediments in greenstone belts provide evidences of oceans formation and indicates that much of the primordial volcanism was underwater.

Pillow andesites at Alitak Bay, Alaska (USA)

Credit: Kodiak Islands NSF project (Western Washington University, University of California-Davis)


Earth’s hydrosphere comes from Volcanic Degassing

#08.1                    #08.2                    #08.3                    #08.4                    #08.5                    #08.6