I'm a bit confused regarding questions which are not allowed here on PF. There is this recent question that was closed - https://www.physicsforums.com/showthread.php?p=4508302#post4508302 It asked if the earth atmosphere's thickness differed, then how will it affect temperature, weather and life forms? I don't understand why is this closed. It requires knowledge of how atmosphere affects earth and more of earth sciences. Similar questions in which you change one aspect and question how would it affect the surroundings, are sometimes closed. Why is this? I don't think this is speculation.