Outgassing

Origin of the Atmosphere and Oceans

Earth’s primitive atmosphere, which consisted mainly of H2O vapor and CO2, formed by a process called outgassing
Gases trapped in the planet’s interior are released by volcanic eruptions
This process continues today  

Water vapor condensed to form clouds and rainwater that formed the oceans
About 3.5 billion years ago, photosynthesizing bacteria began to release oxygen
Oxygen levels steadily increased over time
Eventually oxygen levels were sufficient for ozone to develop in the atmosphere  

Outgassing produced acidic conditions that caused an accelerated rate of weathering of Earth’s rocky surface
Products of this weathering were carried to the oceans, thus increasing the salinity of the oceans
Oceans also served as a depository for carbon dioxide