““Mrs. Turton says that if you lived to be eighty years old, your heart would beat three billion times. I was thinking about that, trying to imagine a number that large. Three billion. Count back three billion hours, and modern humans don’t exist—just wild-eyed cave people, all hairy and grunting. Three billion years, and life itself barely exists. And yet here’s your heart, doing its job all the time, one beat after the next, all the way up to three billion.””
