Question

What gasses did the extensive volcanic eruptions add to the atmosphere in the early in the history of Earth?

Answer 1

Pretty much the same ones that are added by today's volcanoes.

Explanation:

The principal components of volcanic gases are water vapor (H2O), carbon dioxide (CO2), sulfur either as sulfur dioxide (SO2) (high-temperature volcanic gases) or hydrogen sulfide (H2S) (low-temperature volcanic gases), nitrogen, argon, helium, neon, methane, carbon monoxide and hydrogen.
https://en.wikipedia.org/wiki/Volcanic_gas