Cold December evening at sunset. One hundred thousand years ago, the sunset over Manhattan would have looked much the same, but without buildings, bridges, lights, automobiles. Humanity's impact today spreads below the sunset, a great city -- we change the planet in ways benign and malignant, but those terms really define how we change it in its relationship to us. One hundred thousand years from now, the sunset will look the same -- will our species still exist to influence the Earth?