In the previous chapters we have learned the basics on the origin of the atmosphere of the Earth. The main conclusion is that the atmosphere was not captured from the nebular gas but was released from the impacts of planetesimals with the Earth surface. There were huge amounts of water vapor that made up the primitive atmosphere. The subsequent cooling of the planet caused the water vapor to condense and forms the oceans. A good part of the remaining water in the atmosphere was split by photodissociationPhotodissociation with the hydrogen and other light gases escaping. One possible proof of this process is the abundance of the inert gases. The recent formed mantle would release volcanic gases starting about 4.0 billion of years ago that would produce a reducing atmosphereReducing atmosphere which was made up of hydrogen, methane and carbon dioxide that would provide the environment for the origin of life.