Researchers have discovered that Sahara desert, the largest sub-tropical desert after Antarctica and the Arctic, is may be twice as old as they previously thought.

According to researchers, the process of changing the land into desert would have started about seven million years ago.

Climate simulations in the desert show that Tethys Sea would have shrunk and alongside, Arabian Peninsula's level was uplifting. These two situations would have weakened the summer monsoon and formed Sahara desert much longer ago than researchers previously thought.

The study co-authored by Dr. Zhongshi Zhang, a geologist at the Bjerknes Centre for Climate Research in Bergen, has found the evidences from one of the dunes of northern Chad, which is about 7 million years old.
Some other studies also showed the evidence of expanded dry spells in Sahara desert beginning about 8 million years ago.

Climate simulation models made by Dr. Zhongshi Zhang and other researchers show a gradual rearrangement in northern Africa's land. According to the climate simulations of researchers, a rearrangement has been thought to have occurred occur in Tethys Sea.

The study has also shown that the sea would have shrunk about 7 to 11 million years ago, which possibly would have weakened the African summer monsoon. Arabian Peninsula's uplift would have played a significant role in weakening summer monsoon of Africa.

The weakened monsoon would further have weakened westerly winds, which would have become the reason of formation of the Sahara desert.

Researchers said, "Not only did the Tethys shrinkage alter the mean climate of the region, it also enhanced the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extent fluctuations".

Climate changes would have shifted to Asian and African flora and fauna, researchers said. According to Zhongshi Zhang, the research was surprising and they have never thought such a big impact from the sea's retreat.