سؤال قراءة ستيب محلول — الفكرة الرئيسية (تدريب 6023)

(1) New research by tree-ring scientists from Columbia University’s Lamont-Doherty Earth Observatory and West Virginia University may have uncovered the reason why an obscure band of nomadic Mongol horsemen were able to sweep through much of Asia in a few meteoric decades 800 years ago, conquering everything in their path: They enjoyed an unprecedented, and yet-to-be-repeated, 15-year run of bountiful rains and mild weather on the normally cold and arid steppes. (2) By sampling tree rings in the gnarled and twisted Siberian pines in the Hangay Mountains in central Mongolia, the team pieced together a remarkably precise chronology of local climatic conditions stretching from the year 900 A.D. to the present. The study, published in the National Academy of Science offers a new interpretation of why the Mongols suddenly went on the move. (3) The traditional view has been that the Mongols were desperately fleeing harsh conditions in their craggy, mountainous homeland. The Lamont-Doherty team, however, found just the opposite: Between 1211 and 1225. a period that neatly coincides with the rise of Genghis Khan and the Mongol empire, central Mongolia enjoyed a spell of sustained benign weather unlike anything the region has experienced during at least the past 1,100 years and probably much longer. (4) “What makes our new record distinctive is that we can see 15 straight years of above-average moisture,” says the study’s lead author. Neil Pedersen, a tree-ring scientist with the Lamond-Doherty Earth Observatory. “It falls during an important period in Mongol histone and is singular in terms of persistently wet conditions.”