http://www.geocities.com/ramin1102000/13.html That explains what I was thinking... "Richard> "Also, if gravity was low 200 million years ago, which, as you claim, meant larger dinosaurs, how did they breath? Lower gravity mean less air." Ramin> Speaking about increasing of Earth's gravity, my mean is a very gradually increase. As you see in article No. 6 , a very small change of gravity can make lots effects on live animates. So my mean is this, in the past, the gravity was so small, as the atmosphere could be thin remarkably. The interesting this is this in despite of being small for gravity in the past, viscosity and pressure of atmosphere was more than is now. Because viscosity and pressure of atmosphere depends on type of molecules which form it, in addition to the amount of gravity. If atmosphere will be formed of heavy molecules, it's viscosity and pressure will increase. As we know, the combination of atmosphere has been constant from past up to now. High beeing of pressure in the past, is the same another reason for better living of giant animates. Also, the increase of pressure is the same factor which increases the growth speed of animates. "