Unit 1 Great scientists using language课时作业

阅读理解

　　A

　　(2019·蚌埠高三第二次质检)A new study suggests climate conditions in the Sahara Desert, one of the hottest, driest and most deserted areas in the world, have changed from wet to dry about every 20, 000 years.

　　But previous evidence has suggested the Sahara did not always experience such extreme heat and dry conditions.At times, the Sahara changed to a very wet climate.This permitted plants and animals to develop and grow and led to the creation of human settlements.Now, the researchers have discovered more evidence, which, the lead researcher David McGee says, supports the idea that the Sahara's climate kept changing between wet and dry about every 20, 000 years.

　　McGee reported these climate changes were mainly driven by changes in the Earth's axis(地轴) as the planet travels round the sun.This process affects the amount of sunlight between seasons.Every 20, 000 years the Earth receives more strong summer sunlight.When the Earth's axis changes again, the amount of sunlight is reduced.This season change happened continuously every 20，000 years.The other part of the season produced rainy conditions, resulting in a wetter, greener, plant­rich environment.When the rainy activity weakens, the climate becomes hot and dry, like the Sahara remains today.

　　The scientists based their research on dust samples collected from ocean sediment(沉积物) in the Atlantic Ocean bottom off the coast of West Africa.The dust contained layers(层) of ancient sediment built up over millions of years.Each layer could contain tracks of Saharan dust as well as the remains of life forms.This information used to assess over what time period the dust had built up.This led to the overall finding that the Saharan changes from wet to dry climates happened every 20, 000 years.

　　David McGee said that today we only see the Sahara Desert as an extremely deserted and "inhospitable" place.The new study suggests that the area's climate has changed between grasslands and a much wetter environment, and back to dry climates, even over the last quarter million years.McGee says he thinks the latest research can be valuable in studying the Sahara's history as it relates to human settlement.

　　【解题导语】　本文主要介绍了撒哈拉沙漠自然环境的演变，以及其环境改变的原因。

　　1．What does the new study find about the Sahara Desert?

　　A．It is one of the hottest, driest and most deserted areas in Africa.

　　B．It always experiences extreme conditions because of its position.

　　C．Its climate changes between wet and dry about every 20, 000 years.

D．Its environmental conditions stop plants and animals from surviving.