This blue moon of 1999 inspires dreams of a time when the climate was more like January year-round. Fifteen thousand years ago: I stroll in a moist forest of basswood, sugar maple, alder, birch, and spruce munched on by elephants called mastodons. There are no other people. I watch while five thousand years pass, and most cool-wet adapted trees disappear as prairie develops. Farther north a stupendous ice blanket a mile thick melts back toward the Arctic. Now, mammoths are hunted by newly arrived predators who kill at a distance with spears and fire, exterminating them and most other large animals within a few millennia.

Remaining bison are half the bulk of their Ice Age predecessors, and camels, horses, and lions are gone. Sugar maple takes refuge in other ravines, as oaks and junipers invade, invited by the hotter, dryer climate. Human hunters give up on the dwindling herds and settle into farming villages, some cleared from the ravine's forest. Nine more millennia pass, and the rate of change accelerates as newer, paler, human invaders displace the first ones and extirpate bison, black bears, and red wolves in only a century. Then, they use fossil fuels to pave the land, warm the climate, punch holes in the ozone layer, and increase their own cancer and storm damage.