Question

When most people imagine an archetypal desert landscape—with its relentless sun, rippling sand and hidden oases—they often picture the Sahara. But 11,000 years ago, what we know today as the world’s largest hot desert would’ve been unrecognizable. The now-dessicated northern strip of Africa was once green and alive, pocked with lakes, rivers, grasslands and even forests. So where did all that water go? The Sahara has long been subject to periodic bouts of humidity and aridity. These fluctuations are caused by slight wobbles in the tilt of the Earth’s orbital axis, which in turn changes the angle at which solar radiation penetrates the atmosphere. At repeated intervals throughout Earth’s history, there’s been more energy pouring in from the sun during the West African monsoon season, and during those times—known as African Humid Periods—much more rain comes down over north Africa.

a) Sahara will turn green again in some time, and humans cannot influence this
b) Changes in the Earth’s axis cause the changes of Sahara climate
c) The deserts are produced by the changes of the Earth’s axis
d) The water reducing caused Sahara to become a desert

Answer 1

Answer: b) Changes in the Earth’s axis cause the changes in Sahara's climate.

Explanation: The passage discusses the transformation of the Sahara desert over 11,000 years ago when it was once a green and vibrant landscape with lakes, rivers, grasslands, and forests. The change from a lush environment to the arid desert we know today is attributed to periodic fluctuations in the Earth's orbital axis. The slight wobbles in the tilt of the Earth's axis affect the angle at which solar radiation reaches the atmosphere, leading to alternating periods of humidity and aridity in the Sahara's climate. These fluctuations are known as African Humid Periods, during which more solar energy is received during the West African monsoon season, resulting in increased rainfall over North Africa. As the Earth's axis continued to change over time, it influenced the climate of the Sahara, causing it to transition from a green paradise to the arid desert it is today.