What did scientists hypothesize about earths early atmosphere and the way the ocean was formed?

The first ever atmosphere was hydrogen and helium (they call this the primary atmosphere) because these elements are light they were knocked off due to solar storms (charged particles from the sun)

The dense rocks that formed the and the vast temperatures beneath caused many volcanic erupts which spat out carbon monoxide, carbon dioxide, ammonia, hydrogen sulphide, methane and water vapour forming the secondary atmosphere, these heavier elements did not get "knocked" off by solar storms. As the surface of the earth began to cool the water vapour in the atmosphere condensed into perciperation(rain) which ultimately over-time continued to cool the earths surface and make the oceans in the depressions in the earths surface. The oceans are salty because they erode away at the rocks and other elements beneath the surface.

The ocean and rain began to dissolve the ammonia and carbon dioxide in the atmosphere, ultraviolet light shining through the earths atmosphere also broke down water molecules into hydrogen and oxygen and broke remaining ammonia that (in effect is too high) to be dissolved by the ocean into nitrogen and hydrogen.

The combination of nitrogen, hydrogen, oxygen (and of course other small amounts of other elements) is what are atmosphere is now made of.

Makes you wonder what could happen to change our atmosphere in the future, let's hope not too dramatically so we have atleast some time to evolve? :p