Yes on your edit. The origin of Earth's atmospheric nitrogen is thought to be in part due to outgassing (in other words, gas that was stored inside rocks in the early Earth and then released from inside), but is highly uncertain & debated. It's actually so poorly constrained that it may end up being my PhD thesis topic (astrophysics and origins of planetary systems). So not even the experts know, yet, although cometary delivery in cyanide ices from comets is a leading hypothesis (similar to the delivery of water ices).