第40期:人类的发展

Scientists believe that the entire world beyond Africa was populated from descendants of these two hundred individuals. Over time our ancestors multiply and spread out;

to India, onto Asia and into Europe. But while humans head north, a giant wall of ice travels south.

Europe, 40,000 years ago. Homo sapiens arrive, only to find a world that's quickly changing.

It should be the height of summer, but it's getting colder. The plants are frostbitten, and the rivers are frozen.

Natural changes in the Earth's orbit, CO2 levels, and the flow of warm water around the planet conspire to lower the Earth's temperature. The Earth, and its inhabitants, enter an ice age.

Glaciers as high as skyscrapers creep over the northern hemisphere about a foot every day, Slow, and powerful, they sculpt the landscape, gouging out great depressions.

The planet will never look the same again. Now, around twenty thousand years ago, they grind to a halt.