A.The Sahara was a savanna
Northern Africa was a place of trees, grasslands, lakes and people. Today, it is the Sahara — a desolate area larger area than Australia. Lake Yoa, in northeastern Chad, has remained a lake through the millennia and is still a lake today, surrounded by hot desert. Although little rain falls, Lake Yoa’s water is replenished from an underground aquifer. By analyzing thousands of layers sediment in a core drilled from the bottom of this lake, an international team of scientists has reconstructed the region’s climate as the savanna changed to Sahara.