★★★

文章分析：

①For years, the leading theory for what caused the Younger Dryas (a dramatic reversal, about 12,900 years ago, in a global warming trend)?was?a release of water from Glacial Lake Agassiz. ②The theory posited that?this meltwater flooded into the North Atlantic, lowering the salinity and intensity of surface waters enough to prevent them from sinking.?③Ocean currents were changed in such a way that?northward transport of heat in the ocean diminished, and the North Atlantic regions plunged back into near-glacial conditions. ④However, evidence has emerged that the Younger Dryas began long before freshwater flooded the North Atlantic. ⑤Additionally, the temperature changes included by a shutdown in the North Atlantic heat conveyor system?are?too small to explain the Younger Dryas.

S1?觀點(diǎn)

release water?導(dǎo)致??YD

S2?順承觀點(diǎn)

水導(dǎo)致表面水域鹽度和濃度的變化使之不下沉

S3?順承事實

洋流改變

S4?轉(zhuǎn)折事實

YD早就發(fā)生

S5?順承事實

溫度變化不足以解釋YD

①?觀點(diǎn)v1=release water?-->YD

↓

②+③?順承觀點(diǎn)+事實∈v1 ??④+⑤ 轉(zhuǎn)折事實，×v1

①

↓? ? ? ? ? ?? ④+⑤

②+③

題型解析：

1. The author of the passage implies which of the following about the release of water from glacial Lake Agassiz??又是一題定位失效，考場上先做下一題

D

A. The notion that the release occurred has been challenged by more recent findings.（相反，的確發(fā)生了，我要看的是因果關(guān)系，不是這件事本身）

B.The release probably occurred much earlier than scientists have generally assumed.（occur earlier的是YD，不是release，相反）

C.The release would not have been sufficient to cause anytemperature change in the North Atlantic.（最后一句說了溫度發(fā)生過變化，相反）

D.The timing of the release is such that it probably did not trigger the onset of the Younger Dryas.

E.The release was probably unrelated to the global warming trend that was taking place.（沒有證據(jù)，無法證明或證偽，不算implication）

2. The passage is primarily concerned with

A

A. presenting evidence that undermines an explanation

B.?explaining the nature?of a climatological phenomenon（無關(guān)，只是細(xì)節(jié)）

C.?questioning the timing?of a particular event（無關(guān)，只是論據(jù)）

D. discussing a?new explanation?for a phenomenon（沒有證據(jù)，不存在新解釋）

E. suggesting?revisions?to apopular theory（態(tài)度相反/沒有證據(jù)）

背景拓展：

新仙女木事件

The Younger Dryas (c. 12,900 to c. 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum started receding around 20,000 BP. It is named after an indicator genus, the alpine-tundra wildflower Dryas octopetala, as its leaves are occasionally abundant in the Late Glacial, often minerogenic-rich, like the lake sediments of Scandinavian lakes.?

冰河世紀(jì)結(jié)束以后，地球氣候于大約1.7萬年前開始變暖，氣溫逐漸地回升。兩極、北美和北歐的冰川開始消融，海平面逐漸上升，渤海、黃海、挪威海的草原被水淹沒。到了1.3萬年前，北美和北歐的冰雪已經(jīng)融化了相當(dāng)大一部分，南北半球春暖花開，一片繁榮景象。但是，就在這時，在12640年前，氣溫又驟然下降了，世界各地轉(zhuǎn)入嚴(yán)寒，兩極和阿爾卑斯、青藏高原等地的冰蓋擴(kuò)張，許多本來遷移到高緯度地區(qū)的動植物大批死亡。這一次降溫是很突然的，在短短十年內(nèi)，地球平均氣溫下降了大約7、8℃。這次降溫持續(xù)了上千年，直到11500年前，氣溫才又突然回升。這就是地球歷史上著名的新仙女木事件。它的得名由來是：在歐洲這一時期的沉積層中，發(fā)現(xiàn)了北極地區(qū)的一種草本植物——仙女木的殘骸。更早的地層里也有同樣的兩次發(fā)現(xiàn)，分別稱為老仙女木事件和中仙女木事件。

薔薇科仙女木屬?

Evolution of temperatures in the Post-Glacial period, after the Last Glacial Maximum (LGM), showing very low temperatures for the most part of the Younger Dryas, rapidly rising afterwards to reach the level of the warm Holocene. Based on Greenland ice cores.

仙女木事件發(fā)生非常突然，但是至今仍未有足夠的證據(jù)證明其發(fā)生的原因。比較流行的假說是彗星撞擊地球?qū)е聹囟认陆怠?br>