A big-screen, family-friendly (well . . . friendlier) version of the enthralling BBC/Discovery series Planet Earth, Earth follows three animal families—polar bears scavenging for food in the High Arctic; elephants trekking across the Kalahari Desert in search of water; a humpback whale and her young calf on their annual 4,000-mile migration—as they struggle to survive the unrelenting harshness of their disparate climates, a task made all the more difficult by a dangerously warming planet (a point repeated subtly throughout the film). State-of-the-art camera equipment captures images of startling clarity and proximity. There isn’t one frame of CGI. (Much of the material appeared in the television series, but 30 percent of the footage is new.) Death always occurs off-camera, but tension levels remain high: A leopard catches a young gazelle, but the camera turns away before the actual kill; the plight of a polar bear is left to the imagination (but proves heartbreaking nonetheless). Lighter moments also abound. Venturing outside their tree house for the first time, Mandarin ducklings test their tiny wings, only to drop straight down onto the ground. Their fall cushioned by a bed of leaves, they pop up and waddle off, none the worse for wear.