But the Earth is a rather large place and making significant changes (I suppose we can argue over what constitutes significant) to its very atmosphere is a profound thing. We are not the first to do so obviously; the first photosynthesizers left their waste oxygen behind which was rather bad news for a lot of the other life on Earth prior to them. I would have hoped that collectively humans might have more agency than bacteria, but when you look at a chart of carbon dioxide in the atmosphere, it is hard to make that argument.