The atmospheric changes I had in mind were the expansion of human population and burning of wood. I wrote about cultural factors in a sibling comment.
I am not expert in these areas, but the main reason my comment was so brief was that I was working on something else at the time and glanced at HN while waiting for computations to render.
I am not expert in these areas, but the main reason my comment was so brief was that I was working on something else at the time and glanced at HN while waiting for computations to render.