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How might volcanic outgassing have changed Earth’s early atmosphere?
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Volcanic outgassing was the primary driver in the formation of Earth’s early atmosphere, releasing "excess volatiles" such as water vapour, carbon dioxide, and acid gases like hydrogen chloride.123
As the planet’s crust cooled, these gases fundamentally altered the environment:
- Hydrosphere Formation: Once surface temperatures dropped below 100 °C (212 °F), water vapour condensed to form the early oceans.23
- Atmospheric Neutralization: Acid gases reacted with igneous crustal minerals to form sedimentary rocks, a process that neutralized the initial acidity of the surface environment.3
- Greenhouse Effect: Carbon dioxide, which remained in the atmosphere while water condensed, likely existed at concentrations significantly higher than today. This created a strong greenhouse effect that helped keep the early oceans liquid despite a less luminous Sun.13
- Compositional Shift: Molecular oxygen was notably absent from volcanic products. Over time, as carbon dioxide was consumed by weathering and water vapour condensed, molecular nitrogen became the most abundant gas in the atmosphere.13
It is important to note that volcanic outgassing did not produce free oxygen; the oxygenated atmosphere we rely on today only emerged later through photosynthetic organisms.13