What was the composition of the primary atmosphere of the planet?

The primary atmosphere of the Earth consisted mainly of water vapor, hydrogen and ammonia. Under the influence of ultraviolet radiation from the sun, water vapor decomposed into hydrogen and oxygen. To a large extent, hydrogen went into outer space, oxygen reacted with ammonia, and nitrogen and water formed. At the beginning of geological history, the Earth, thanks to the magnetosphere that isolated it from the solar wind, created its own secondary carbon dioxide atmosphere. Carbon dioxide came from the bowels during intense volcanic eruptions.