What do we measure when we measure time? The gloomy answer from Hawking, one of our most implacably cheerful scientists, is that we measure entropy. We measure changes and those changes are all for the worse. We measure increasing disorder. Life is hard, says science, and constancy is the greatest of miracles.

Of course anyone who truly loves books buys more of them than he or she can hope to read in one fleeting lifetime. A good book, resting unopened in its slot on a shelf, full of majestic potentiality, is the most comforting sort of intellectual wallpaper.

Evolution as described by Charles Darwin is an scientific theory, abundantly reconfirmed, explaining physical phenomena by physical causes. Intelligent Design is a faith-based initiative in rhetorical argument. Should we teach I.D. in America's public schools? Yes, let's do - not as science, but alongside other spiritual beliefs, such as Islam, Zoroastrianism and the Hindu Idea that Earth rests on Chukwa, the giant turtle.

By the cold Darwinian logic of natural selection, evolution codifies happenstance into strategy.

You can hike into the Yellowstone backcountry. You can camp in the Yellowstone backcountry. You can take food into the Yellowstone backcountry, and you're surrounded by grizzly bears. And it's - it's a very, very thrilling, peculiar situation. Every sound that you hear in the night, you wonder is this a grizzly bear coming to tear into my tent?

If you're Maasai Mara National Park in Kenya, if you're in Serengeti National Park in Tanzania, you don't get out of your vehicle and go walking around amid the lions and the leopards. You stay in your Land Rover. You stay in your safari van, and you look out the windows or you look out the pop top at these animals. I know by experience how badly that can work out if you violate those guidelines.

Whether you like the label 'Anthropocene' or not, whether you find the prospect of what it signifies inevitable or appalling (or both), the time has come to address its implications, as these thoughtful, battle-tested authors attempt to do. The time has long since come.