In the early history of the Earth, the atmosphere was dominated by carbon dioxide (CO2CO_2CO2) and nitrogen, with surface temperatures regulated by a strong greenhouse effect. Over geological timescales, atmospheric CO2 CO_2\,CO2 levels decreased dramatically.
Which planetary-scale process was primarily responsible for this long-term drawdown of atmospheric carbon dioxide?
Direct thermal decomposition of CO2CO_2CO2 into elemental carbon and oxygen gas in the thermosphere.
The weathering of silicate rocks by acidic rainfall, leading to the deposition of carbonate minerals on the seafloor.
The physical entrapment of gaseous carbon dioxide inside clathrate hydrates within the deep oceanic crust.
The reduction of carbon dioxide by hydrogen gas during intense volcanic outgassing events to form methane.