Examine the power that water, sunshine, and the seasons have over animals and ecosystems. Zoom in on a critical move by a polar bear family, a mass caribou migration, an epic elephant trek, and the ebb and flow of life for master predators.

Shudder in the presence of the geological and volcanic forces that have created Earth's mightiest mountain ranges. Meet extreme animal climbers in the Andes and the Himalayas, and track the highest land predator on Earth, the shy snow leopard.

Follow rivers from their mountain sources to the sea and get a look at the unique wildlife that live in them. Dive with Earth's only freshwater seal in fathomless Lake Baikal, spy on giant salamanders in Japan, and frolic with Amazon river dolphins.

Slide into the shady realm of subterranean spaces, including a Mexican cave that's as deep as the Empire State Building and a crystal-lined American cavern. Observe millions-strong bat colonies, blind fish, and troglodytes who never see daylight.

Trek across the arid desert climates that cover 30 percent of our world. Discover how snow-eating Bactrian camels in the Gobi, dew-licking guanacos in Chile's Atacama, and some of Africa's largest mammals get by in these inhospitable landscapes.

Plunge into winter darkness and blink in the never-ending summer daylight at the world's polar extremes. Cast a wide net with humpback whales, ply the sea ice with breeding emperor penguins, and stalk a hungry polar bear as his world melts away.