A mother polar bear teaches her two cubs to hunt in the Arctic. An African elephant herd crosses the Kalahari Desert in search of water. A humpback whale and her calf migrate thousands of miles from calving grounds in the tropics to feeding grounds in the Southern Ocean. "Earth" loosely weaves together the tales of these three animal families’ struggle to survive over the span of a year. It’s the first feature film from Disney's new division, Disneynature, and marks the company’s return to family-friendly nature documentaries, a genre that it created with its “True Life Adventures” series in the 1950s. About half of the "Earth" footage will likely be familiar to the many moviegoers who have seen the Discovery Channel’s series, “Planet Earth,” which came out in 2007. In fact, Disneynature repackaged much of that footage for the film. But rather than feeling stale, the spectacular cinematography comes to life on the big screen. The film touches lightly on the creatures’ changing environments—there are brief mentions of melting polar ice caps and desertification, for instance. But the thrust of the film, narrated by James Earl Jones in his unmistakable sonorous voice, is really the exploits of the animals, and not just the three families. There are also plenty of asides, from shots of caribou migrating across the tundra, to mandarin ducklings’ first flight, to incredible slow-motion footage of a cheetah, muscles rippling, chasing down a gazelle. In this instance, and several others, the audience doesn’t actually see the animal’s bloody death. It is, after all, a G-rated production. “Earth” opened Wednesday, April 22.