The sands of the Sahara seem endless – in time as much as distance – but the world's largest desert is of surprisingly recent origin. Lake Chad's borders reveal just how dramatically the region's climate has changed; only 6,000 years ago this inland sea was larger than North America's five Great Lakes combined, making it the largest freshwater lake in the world.
Lake Chad still exists, indeed 70 million people depend on it for water. However, it is a shadow of its former self, having declined dramatically since the 1960s. Even the mid-20th century version was small compared to its ancestor, known as Palaeolake Mega-Chad.
The existence of a giant paleolake is well established, but a paper in the Proceedings of the National Academy of Sciences has mapped its changes over a period of 15,000 years, revealing the North African climatic history in the process.