Can you walk on the ground, not in the clouds? We have civilizations because we changed the environment. Somewhere 12,000 years ago, give or take a few thousand years, humans started agriculture, converting prairies into arable land. Draining marshlands and burning forests was the next step. Building cities came along. Nomads were the last humans who did not cause any planetary destruction. If you want me to go back there, I am not for it.