GWD-11-Q41

伊布拉莫维琨

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old. Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.
E(D)
Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?

A. Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.
B. Another campsite was found in New Mexico with remains dated at 16,000 years old.
C. A computer simulation of glacial activity showed that it would already have been impossible for humans to travel south overland from Alaska 18,500 years ago.
D. Using new radiocarbon dating techniques, it was proved that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge at least 11,400 years ago.
E. Studies of various other hunting-gathering populations showed convincingly that, once the glaciers allowed passage, humans could have migrated from Alaska to Colorado in about 20 years.

Answer: D

没思路啊 请大虾指点

sundayydf

我做这题也选错了，选了C，发现C只是说18500年前，而跟18000差了500年，所以insufficient，看来数字和percentage真实在做逻辑的时候真实非常关键；D答案直接attack premise，说新技术证实了有一条ice-free通道（不受glacial activity影响）让人类迁徙成为可能

hebelong

排除无关剩下C,D
C. A computer simulation of glacial activity showed that it would already have been impossible for humans to travel south overland from Alaska 18,500 years ago.没可能……18500年前

原文"humans must have come to the Americas more than 18,000 years ago." 18000前
二者没矛盾，不削弱

D. Using new radiocarbon dating techniques, it was proved that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge at least 11,400 years ago. —— 允许11400年前

prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago
----------受阻止在18000到11000年前，“11400年前”在之间吧，矛盾了，PICK IT !

不知道说得是否清楚，欢迎指教~

wsgy

因为冰川阻止人类在18000到11000年前这段时间向南迁徙，而矿的年代正好处于这个区间。所以得出结论，人类肯定是18000前就跑到南边儿来了。

选项D否认了人类没法在18000到11000年前这段时间向南迁徙的说法，因为人类可以利用距近11400（早于11200）的无冰走廊来到南方。

明白？

leadlife

premise1：我们可以知道在11200年前人类已经在使用这个矿了，因为发现了矿在hearth（灶台）这里，说明11200年前这个时间点再往前人类肯定就在这里了。（地点是南边）
premise2：glaciers阻止了人类在11000年前-18000年前这段时间里往南迁徙来到这个发现有矿的hearth的地方。（说明11800年前是可以过来的）
conclusion：人类肯定是18000年前就已经迁徙到这里了（南方）
weaken思路：证明人类在11200年前（用矿的时候）-18000年前就可能已经在南方这里了。

D选项：这个通道至少在11400年前年就有了————这样就可以推出：人类有可能在11400年前就通过这个通道过来了，从而weaken了结论。

A：把这个矿的使用时间往前推到11400年前，不能削弱。
B：无关
C：18500年前不能南移，不能削弱18000年前人类就在那里了，可以在18500年前---18000年前这段时间到这里。
E：无关