[turnipsock (OP)]

The Earths atmosphere is made up of about 80% Nitrogen...where does that come from?

Oxygen and Carbon Dioxide come from various sources, but Nitrogen never gets a mention...why?

[JimBob]

"In the beginning ..."

I'll be unable to give much of a rational explanation except to mention the assumption that the original atmosphere of earth was mostly a methane-ammonia concoction. Were it not weighted heavily to the ammonia end, life would not have formed Amino acids, the building blocks of life, which are made of a carboxyl group(s) and an ammonia atom (with one hydrogen missing).

Yet all of this is just the accepted speculation of 3-4 generations of organic life scientists - I know of little concrete evidence from the fossile record of the conditions of the atmosphere during the Archean geologic period.

 

[Soul Surfer]

The glib answer is that it came from the same stars that made the carbon and the carbon.  There is just quite a lot of nitrogen around in the universe