Continuing its buildup to this Saturday’s premiere of Blue Planet II – which, by the way, I recommend as enthusiastically as I recommend anything – BBC America today presents a marathon repeat of yet another of its previous nature documentary triumphs, 2007’s Planet Earth: Life. All 10 episodes are shown, in order, then repeated again beginning at 8 p.m. ET. Sir David Attenborough, the best in the business, narrates.