It has generally been agreed that desert began to form in northern Africa about 3 million years ago, leading to today’s Sahara. But now scientists discovered it may be twice as old as  originally thought, with desertification starting around 7 million years ago.

Climate simulations suggest the shrinking of the Tethys Sea coupled with the uplift of the Arabian peninsula weakened the summer monsoon, forming the vast desert that exists today much longer ago than previously concluded.

The research, published in Nature, was co-authored by Dr Zhongshi Zhang, a palaeoclimatologist at the Bjerknes Centre for Climate Research inBergen,Norway. The evidence comes partially from dune deposits in northern Chad that were estimated to be seven million years old.

Other studies also found evidence for extended dry period in the region starting eight million years ago. The reason why this was so was not known, but now Dr Zhang says he may have an answer. His team’s climate simulations suggest a gradual rearrangement of land masses in northern Africa. One particular shift was thought to occur in the Tethys Sea that once bordered northern Africa. The sea gradually shrunk around seven to 11 million years ago, and it’s thought this may have weakened the African summer monsoon. The uplift of theArabian peninsulawas also thought to play a part. The reduction of the monsoon would in turn have weakened westerly winds, shifting a flow of moisture from the tropical Atlantic further south.

This suggests the desertification, and ultimately the formation of the Sahara desert, may have formed earlier than thought. ‘Not only did the Tethys shrinking change the average climate of the region, it also increased the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extended waving,’ the researchers write.

‘These important climatic changes probably caused the shifts in Asian and African animals and plants development during the same period.'

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1.What is the means by which scientists made the new discovery of Sahara Desert?

A Studying historical records.

B Making long-term observation.

C Going on archeology.

D Making climate simulations.

解析：选D。D 细节理解题。根据文章第二段Climate simulations suggest…可知，本文主要介绍了电脑模拟的气候变化与地质变化对于撒哈拉沙漠形成的影响。科学家的研究手段是电脑模拟。

2.What was the consequence of the uplift of the Arabian Peninsula?

A It led to the reduction of the Tethys Sea.

B It made the summer monsoon weaker.

C It formed the duns in northern Chad.

D It led to rearrangement of land masses.

解析：选B。B 细节理解题。根据文章第二段…coupled with the uplift of the Arabian peninsula weakened the summer monsoon可知，阿拉伯半岛地势抬高，减弱了非洲夏季季风，减少了降雨量，为形成沙漠提供了气象条件。

3.What was the cause of the Sahara extended waving?

A The shrinking of the Tethys Sea.

B Orbital forcing.

C The westerly winds.

D The African monsoon.

解析：选D。D 细节理解题。根据文章倒数第二段…the sensitivity of the African monsoon to orbital forcing, which subsequently became the major driver of Sahara extended waving可知，非洲季风受轨道驱动力影响，使撒哈拉沙漠某些区域形成波动。

4.What can be implied in the passage?

A Sahara Desert formed after a serial of geographical and climatic incidents.

B Orbital forcing played a part in the increase of the desert area on the earth.

C The previous research of the formation of Sahara Desert was misleading.

D Seasonal winds played the key role in the formation of the Sahara Desert.

解析：选A。A 推理判断题。综合全文可知，撒哈拉沙漠的形成与古地中海的缩小、阿拉伯半岛的抬升，夏季季风与西风的减弱，甚至与轨道驱动力有关，由此判断，撒哈拉沙漠是一系列地质与气候事件的综合结果。

5.What can be the best title of the passage?

A Shrinking of Sea Caused the Form of Sahara Desert.

B New Discovery Proved Previous Study of Sahara Desert Wrong.

C Climate Simulation Found Sahara Desert Older.

D Space Power Left Mark on World’s Greatest Desert.

解析：选C。C 主旨大意题。通读全文可知，文章的主要内容是，科学家通过模拟实验发现撒哈拉沙漠的形成时间早于早期研究。故选C。