Why are nitrogen and argon present in the earth's atmosphere?
The outgassings of the Earth was stripped away by solar winds
early in the history of the planet until a steady state was
established, the first atmosphere. Based on today's volcanic
evidence, this atmosphere would have contained 80% water vapor, 10%
carbon dioxide, 5 to 7% hydrogen-sulfur, and smaller amounts of
nitrogen, carbon monoxide, hydrogen, methane and inert gases.