I guess I'm thinking more along the lines of very early atmospheric and oceanic conditions. It seems that there is some disagreement on the oxygen content of the atmosphere and the gravitatioal attraction. From what I've read on these threads lately there are fossils that support both the oxygen rich and oxygen poor atmosphere. There was also the discussion about a flying creature that would have required a denser atmosphere to fly which would have required a stronger gravitational attraction. Aren't there also dinosaurs which would have required less graviation to survive; for example: for the blood to flow up their necks?
I do believe that different conditions have existed at different times throughout the earth's history. And some of that is confirmed by geological processes. BUT again, things have been different at different times. We just don't know EXACTLY when. With all sorts of flying things now, I don't know about the flying stuff.