How have volcanoes, earthquakes, and tectonic plates changed the earth's atmosphere?
I'm assuming that all three of the events you listed in your question deal with the gases released during a volcano, earthquake, and the movement of tectonic plates (which produce volcanoes and earthquakes). There are three gases in particular that have potential to alter the atmosphere:
H20: During the earth's early history, so much water was released by the boiling, churning surface, that ALL water present on earth today is a result of that steam. H20 has been also linked to climate effects. Too much H20 (in the form of clouds) covers the surface below, making it cooler. In addition, clouds eventually lead to a lot of rain.
CO2: After water this is the next big gas. Today, CO2 makes up less that 0.3% of the atmosphere. Much debate continues as to people's contribution to the increasing (small but increasing) amount of CO2 in the atmosphere. CO2 is definitely a greenhouse gas (as is water too by the way). The question is: how much does atmospheric CO2 influence temperature here on earth? I leave that one to greater minds. (Note: in earth's early history, as much as 33% of the atmosphere was CO2--bad for you and me, but great if you're a plant!)
SO2: Pretty much bad any way you look at it. It is a greenhouse gas and causes acid rain. However, life has been found that actually flourishes in boiling water that is made highly acidic from SO2 (creating sulfuric acid). Some speculate that this gas (which was much more prevalent in earth's early atmosphere) was essential for life to begin. If you study the chemical elements needed in DNA and RNA, you will find that sulfur, although in minor amounts, is essential for RNA and DNA to maintain their twisted ladder structure.
Hope this long digression helps.