Columbia University

When the Sahara turned to sand

The Sahara wasn't always a desert. Trees and grasslands dominated the landscape from roughly 10,000 years ago to 5,000 years ago. Then, abruptly, the climate changed, and north Africa began to dry out.

Nov 11, 2013 4.4 / 5 (12) 4

Tackling an Ice Age mystery

In the northern hemisphere, ice sheets ebb and flow in 100,000-year cycles, driven by varying amounts of sunlight falling on Earth's surface as its orbit and orientation toward the sun changes. But astronomical variations ...

Sep 05, 2013 4.8 / 5 (5) 0