It is one of the most man-made spaces on the planet, but everything in New York from the height of the skyscrapers to the way the subway was constructed to the position of the harbor is governed by the extraordinary forces outside of man's control.

Why do we have ice ages and when is the next one due? Chart the progress of different ice ages through the history of our planet, from Snowball Earth hundreds of millions of years ago to the recent ice ages.

Not so long ago, civilization learned that it was no match for just a few degrees drop in temperature. Scientists call it the Little Ice Age--but its impact was anything but small.

A certain mystique lingers in its very name. It's a haunting and hostile arena with a past as captivating as its landscape. In this desert blanketing 11 nations in Northern Africa, nature has crafted a world of mesmerizing desolation and across its scorching sands humanity has dared to carve history. Our cameras explore a land of mirage and myth--from a mountain fortress of ancient freedom fighters to a vast stadium filled with gladiators' gore to the vibrant chaos of a camel auction to the fabled metropolis of Timbuktu. Historians chronicle how a devastating climate change turned a lush savanna into the world's harshest desert. The Sahara...sinister and seductive, mythic and mysterious...as tantalizing and elusive as a mirage.

The story of a century-and-a-half of tireless research that led humans to discover their ape-like origins. In this 2-hour special, we review several stories of discovery, each a crucial turning point in the understanding of our pre-historical past. Our heroes are the men and women who uncovered the clues, often after backbreaking and obsessive labor in some of Earth's most hostile environments. Their stories are told with dramatic reconstructions and tantalizing glimpses of the lives of ancestral humans they uncovered, together with newspaper headlines, news reports and archive footage, and expert interviews. In the course of this enthralling journey, we uncover stunning facts, wild theories, and compelling conclusions unearthed by pioneering investigators of human origins. This is the story of how 150 years of sweat and toil brought our extraordinary origins into the light.