Earth’s atmosphere formation began 4.57 Ga ago, when the solar wind stripped
off the Hydrogen and Helium. Volcanic gases (water, carbon dioxide, sulfur
dioxide, nitrogen, ammonia) accumulated in 3.9 Ga, causing a secondary
atmosphere to form. As the planet began to cool, condensed rain formed what is
now ocean water, overall level of carbon dioxide decreased, and stable N2 level
increased. Photosynthetic cyanobacteria also decreased levels of CO2, and thus
added O2 to the atmosphere, yielding to the formation of many other life forms
over a span of time.
Ozone comes from a two step reaction, with normal oxygen O2 reacting with the
sun, which separates the two into individual atoms. Then the individual 0 atoms
react with another oxygen atom, 02, to form ozone, 03. Ozone is important
because it absorbs radiation from solar radiation.
The air is made of 78% Nitrogren, 21% Oxygen, and 1% of the following: argon,
carbon dioxide, methane, sulfur dioxide, ozone, and radon.