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通过比较山顶与山脚的叶子化石，得出了一个惊人的结论。那就是在60万年前，落基山脉的高度应该是今天的两倍。为什么是这样的？那么大的山怎么会消失一半呢？Daisy很好奇，我要听下文啦！
After the Rockies emerged from the sea, it took them 10 million years to rise. Sixty million years ago, they reached spectacular heights of 28,000 feet, rivaling the Himalayas today. The deep history of the Rocky Mountains is beginning to take shape.
A weak line in the crust explains why the Rockies rose 500 to 1000 miles inland. Fossil leaves show that the young Rocky Mountains were once nearly twice their size. Half of the rock that formed them originally has vanished. Scientists are now trying to unravel the processes that cut them down to the size they are today.
One hundred million years ago, a vast inland sea covered the area where the American Rockies stand tall today. Seventy million years ago, the sea retreated as the Rockies began to rise. Sixty million years ago, the Rocky Mountains reached their pinnacle, towering into the sky with peaks over 28,000 feet high, rivaling the Himalayas.
Since then, the entire mountain range has lost nearly half its height. Geologists investigating the history of the Rockies are trying to discover what happened to the billions of tons of rock that went missing. The investigation starts with a mystery at the Owl Creek Mountains in the Wyoming Rockies. The Mountains are sliced by a river that has formed a deep canyon.
"Well, the Wind River is very perplexing. It chose to take a straight path right through the core of a major mountain range. This is not the way that rivers normally act. Usually it will take the easiest route which is a downhill. But this river cut right through a major mountain range and has been a mystery. It is a very perplexing issue to early geologists in the region."
This river led to confusion as early as 1806 when Marry Whether Louis and William Clark mapped the area during their famous expedition to explore uncharted territory.
小编有约：哦，本期的听力中有一个非常著名的“刘易斯与克拉克远征”，Daisy简单介绍介绍，刘易斯与克拉克远征（Lewis and Clark expedition，1804年–1806年）是美国国内首次横越大陆西抵太平洋沿岸的往返考察活动。领队为美国陆军的梅里韦瑟·刘易斯上尉（Meriwether Lewis）和威廉·克拉克少尉（William Clark），该活动是由杰斐逊总统所发起。大家应该猜到，由总统发起的，一定是想夺得这里的土地啦！呵呵~~具体详情就自己查啰。
课后题目：Daisy想让大家自己了解了解美国的地理，你能告诉我，文中出现的“ Owl Creek Mountains”在美国哪里吗？它有什么特征呢？
