A world map published by the National Geographic Society has this notation: “Earth’s mass is 6.6 sextillion tons.” And what supports all that weight? Nothing. The planet we inhabit spins on its axis at 1,000 miles per hour as it hurtles through space in its orbit around the sun. But it’s easy for that to remain unnoticed in the midst of our daily concerns about health, relationships, and how to pay the bills.