Sir David Attenborough takes us deep into caves this week.

Delving in to the deep dark places beloved on bears and Batman

There is a deep and abiding truth resonating in the title of Attenborough's Planet Earth (One, 7.30pm): it truly is David Attenborough's planet, and we're just living on it. Which we might not be able to do for all that much longer, and you get the sense that Sir David is a little vexed by this. To be honest it's always a little bit surprising — a pleasant surprise, I hasten to add — when you remember that Attenborough is still alive, and one can't shake the impression that he has simply decided he's not shuffling off the coil until the rest of us get our bloody act together. Happily, this means he should be here for some time yet. Unhappily, of course, we won't be. But at least when the gigantic hyper-intelligent prawn-people who evolve to inhabit the blighted planet in millions of years look back at the records of the feckless land-apes who came before them, they'll be able to take a squiz at programs like this and see what a cracker of a planet Earth used to be.