托福閱讀真題Official 49 Passage 1（五）

托福閱讀真題Official 49 Passage 1（五）

Ancient Coastlines

Information on past climates is primarily of relevance to archaeology because of what it tells us about the effects on the land and on the resources that people needed to survive.The most crucial effect of climate was on the sheer quantity of land available in each period,measurable by studying ancient coastlines.These have changed constantly through time,even in relatively recent periods,as can be seen from the Neolithic stone circle of Er Lannic,in Brittany,France(once inland but now half submerged on an island)or medieval villages in east Yorkshire,England,that have tumbled into the sea in the last few centuries as the North Sea gnaws its way westward and erodes the cliffs.Conversely,silts deposited by rivers sometimes push the sea farther back,creating new land,as at Ephesus in western Turkey,a port on the coast in Roman times but today some five kilometers inland.

Nevertheless,for archaeologists concerned with the long periods of time of the Paleolithic period there are variations in coastlines of much greater magnitude to consider.The expansion and contraction of the continental glaciers caused huge and uneven rises and falls in sea levels worldwide.When the ice sheets grew,the sea level would drop as water became locked up in the glaciers;when the ice melted,the sea level would rise again.Falls in sea level often exposed a number of important land bridges,such as those linking Alaska to northeast Asia and Britain to northwest Europe,a phenomenon with far-reaching effects not only on human colonization of the globe but also on the environment as a whole—the flora and fauna of isolated or insular areas were radically and often irreversibly affected.Between Alaska and Asia today lies the Bering Strait,which is so shallow that a fall in sea level of only four meters would turn it into a land bridge.When the ice sheets were at their greatest extent some 18,000 years ago(the glacial maximum),it is thought that the fall was about 120 meters,which therefore created not merely a bridge but a vast plain,1,000 kilometers from the north to the south,which has been called Beringia.The existence of Beringia(and the extent to which it could have supported human life)is one of the crucial pieces of evidence in the continuing debate about the likely route and date of human colonization of the New World.

The assessment of past rises and falls in sea level requires study of submerged land surfaces off the coast and of raised or elevated beaches on land.Raised beaches are remnants of former coastlines at higher levels relative to the present shoreline and visible,for instance,along the Californian coast north of San Francisco.The height of a raised beach above the present shoreline,however,does not generally give a straightforward indication of the height of a former sea level.In the majority of cases,the beaches lie at a higher level because the land has been raised up through isostatic uplift or tectonic movements.Isostatic uplift of the land occurs when the weight of ice is removed as temperatures rise,as at the end of an ice age;it has affected coastlines,for example,in Scandinavia,Scotland,Alaska,and Newfoundland during the postglacial period.Tectonic movements involve displacements in the plates that make up Earth’s crust;Middle and Late Pleistocene raised beaches in the Mediterranean are one instance of such movements.

Raised beaches often consist of areas of sand,pebbles,or dunes,sometimes containing seashells or piles of debris comprising shells and bones of marine animals used by humans.In Tokyo Bay,for example,shell mounds of the Jomon period(about 10,000 to 300 B.C.E.)mark the position of the shoreline at a time of maximum inundation by the sea(6,500–5,500 years ago),when,through tectonic movement,the sea was three to five meters higher in relation to the contemporary landmass of Japan than at present.Analysis of the shells themselves has confirmed the changes in marine topography,for it is only during the maximum phase that subtropical species of mollusc are present,indicating a higher water temperature.

Question 9 of 14

According to paragraph 3,why is the height of a raised beach not a straightforward indicator of past sea level?

A.The height of the beach may have been raised or altered by human interventions in the shore environment.

B.The height of the beach may be the result of erosion over a brief period of time.

C.It is difficult to assess if the sea actually existed at that level for any significant period of time.

D.The surface of Earth may have shifted,moving the beach from its original position.

正確答案：D

題目詳解

題型分類：事實(shí)信息題

原文定位：根據(jù)straightforward indicator定位到第三段第三句（原文高亮），此句說上升海灘高度通常并不能簡單說明從前海平面的高度。其原因位于后面一句，即上升海灘在大多數(shù)情況下是被均衡上升或構(gòu)造運(yùn)動(dòng)抬起來的。

選項(xiàng)分析：

D選項(xiàng)說地球表面可能從原有位置移動(dòng)了沙灘shifted,moving the beach，這與原文中的isostatic uplift（均衡上升）或tectonic movements（構(gòu)造運(yùn)動(dòng)）一致。

A選項(xiàng)的human interventions in the shore environment（人類對海岸環(huán)境的干預(yù)）在原文中沒有提及，屬于無中生有。

B選項(xiàng)的erosion over a period of time（一段時(shí)間的侵蝕）在原文中沒有提及，屬于無中生有。

C選項(xiàng)的if the sea actually existed at that level（在那個(gè)高度海洋是否真實(shí)存在）在原文中也沒有提及，屬于無中生有。

Question 10 of 14

According to paragraph 3,which of the following causes an isostatic uplift?

A.Shifts in Earth’s crust

B.A decrease in the pressure of thick ice sheets

C.A decrease in temperature

D.Changes in sea level

正確答案：B

題目詳解

題型分類：事實(shí)信息題

原文定位：根據(jù)isostatic uplift定位到第三段倒數(shù)第二句“Isostatic uplift of the land occurs when the weight of ice is removed as temperatures rise”，這句講到陸地的均衡上升發(fā)生在氣溫上升、冰川重量移除的時(shí)候。

選項(xiàng)分析：

B選項(xiàng)the pressure of thick ice sheets與原句the weight of ice對應(yīng)，deceased與原句is removed對應(yīng)，講厚厚的冰蓋所造成的壓力減少了，與原句意思相同。

A選項(xiàng)張冠李戴。Shifts in Earth’s crust（地殼的移動(dòng)）屬于構(gòu)造運(yùn)動(dòng)，而不是均衡上升的原因。

C選項(xiàng)A decrease in temperature（溫度下降）與原句temperatures rise矛盾。

D選項(xiàng)Changes in sea level（海平面變化）原句沒有提及，屬于無中生有。

>> 雅思 托福 免費(fèi)測試、量身規(guī)劃、讓英語學(xué)習(xí)不再困難<<