(1-9 p.m. ET) Any marathon of this nature series would be worth watching, but this one is TV Worth Hearing as well. For this special Earth Day showing, Discovery Channel is presenting this series with its original narration by Sir David Attenborough, not the swapped-out U.S. narration by Alec Baldwin. And it makes the series seamless, since tonight’s special finale – shown for the first time by Discovery – is hosted by Attenborough on-camera. It’s called On Thin Ice, and it’s the respected naturalist’s personal view of how the world has changed, and why, in the more than 50 years he’s been exploring it. For related TVWW coverage, see my Bianculli’s Blog review HERE and Jane Boursaw’s just-posted Reel Life with Jane overview HERE.