Scientists believe the Sahara desert is twice as old as we previously thought. Science books generally say the Sahara is around three million years old. However, a new study from a centre for climate research in Norway says it could be around seven million years old. Researchers used computers to try and calculate when large parts of North Africa became desert. Their tests showed that global warming seven million years ago dried a lot of the land in what is today the African nation of Chad. A sea called the Tethys Sea started shrinking. This made the African summer monsoons less frequent, which helped form sand dunes in Chad. The scientists say this is how the Sahara first started.
The Sahara is one of the world's best-known and largest deserts. It covers about 10 per cent of the whole African continent and forms large parts of Algeria, Chad, Egypt, Sudan and other nations. The sands stretch from the Atlantic Ocean in the west to the Red Sea in the east. Not everyone agrees that the Sahara is as old as the Norway research says it is. Stefan Kröpelin, a geologist in Germany, says real geological evidence is needed to be sure. He said the Norway research is based on numbers and not evidence, saying: "Nothing you can find in the Sahara is older than 500,000 years old". He added that our knowledge of the Saharan climate is only from 10,000 years ago and that our knowledge is "full of gaps".