托福閱讀真題Official 45 Passage 1（五）

托福閱讀真題Official 45 Passage 1（五）

The Beringia Landscape

During the peak of the last ice age,northeast Asia(Siberia)and Alaska were connected by a broad land mass called the Bering Land Bridge.This land bridge existed because so much of Earth’s water was frozen in the great ice sheets that sea levels were over 100 meters lower than they are today.Between 25,000 and 10,000 years ago,Siberia,the Bering Land Bridge,and Alaska shared many environmental characteristics.These included a common mammalian fauna of large mammals,a common flora composed of broad grasslands as well as wind-swept dunes and tundra,and a common climate with cold,dry winters and somewhat warmer summers.The recognition that many aspects of the modern flora and fauna were present on both sides of the Bering Sea as remnants of the ice-age landscape led to this region being named Beringia.

It is through Beringia that small groups of large mammal hunters,slowly expanding their hunting territories,eventually colonized North and South America.On this archaeologists generally agree,but that is where the agreement stops.One broad area of disagreement in explaining the peopling of the Americas is the domain of paleoecologists,but it is critical to understanding human history:what was Beringia like?

The Beringian landscape was very different from what it is today.Broad,windswept valleys;glaciated mountains;sparse vegetation;and less moisture created a rather forbidding land mass.This land mass supported herds of now-extinct species of mammoth,bison,and horse and somewhat modern versions of caribou,musk ox,elk,and saiga antelope.These grazers supported in turn a number of impressive carnivores,including the giant short-faced bear,the saber-tooth cat,and a large species of lion.

The presence of mammal species that require grassland vegetation has led Arctic biologist Dale Guthrie to argue that while cold and dry,there must have been broad areas of dense vegetation to support herds of mammoth,horse,and bison.Further,nearly all of the ice-age fauna had teeth that indicate an adaptation to grasses and sedges;they could not have been supported by a modern flora of mosses and lichens.Guthrie has also demonstrated that the landscape must have been subject to intense and continuous winds,especially in winter.He makes this argument based on the anatomy of horse and bison,which do not have the ability to search for food through deep snow cover.They need landscapes with strong winds that remove the winter snows,exposing the dry grasses beneath.Guthrie applied the term“mammoth steppe”to characterize this landscape.

In contrast,Paul Colinvaux has offered a counterargument based on the analysis of pollen in lake sediments dating to the last ice age.He found that the amount of pollen recovered in these sediments is so low that the Beringian landscape during the peak of the last glaciation was more likely to have been what he termed a“polar desert,”with little or only sparse vegetation.In no way was it possible that this region could have supported large herds of mammals and thus,human hunters.Guthrie has argued against this view by pointing out that radiocarbon analysis of mammoth,horse,and bison bones from Beringian deposits revealed that the bones date to the period of most intense glaciation.

The argument seemed to be at a standstill until a number of recent studies resulted in a spectacular suite of new finds.The first was the discovery of a 1,000-square-kilometer preserved patch of Beringian vegetation dating to just over 17,000 years ago—the peak of the last ice age.The plants were preserved under a thick ash fall from a volcanic eruption.Investigations of the plants found grasses,sedges,mosses,and many other varieties in a nearly continuous cover,as was predicted by Guthrie.But this vegetation had a thin root mat with no soil formation,demonstrating that there was little long-term stability in plant cover,a finding supporting some of the arguments of Colinvaux.A mixture of continuous but thin vegetation supporting herds of large mammals is one that seems plausible and realistic with the available data.

Question 9 of 14

In paragraph 5,the amount of pollen in Beringian lake sediments from the last ice age is used to explain

A.how long the ice age lasted

B.how important pollen is as a source of food

C.how many different kinds of plants produce pollen

D.how little vegetation must have been present at that time

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)the amount of pollen定位到第五段第二句

選項(xiàng)分析：

D選項(xiàng)little vegetation對(duì)應(yīng)定位句little or only sparse vegetation，D選項(xiàng)正確。

A選項(xiàng)how long無中生有。

B選項(xiàng)a source of food無中生有。

C選項(xiàng)different kinds of plants無中生有。

Question 10 of 14

According to paragraph 5,how did Dale Guthrie use the information about radiocarbon analysis of bones from Beringian deposits?

A.To suggest that Colinvaux should have used different methods to measure the amount of pollen in ice-age lake sediments

B.To argue that the large Beringian mammals must have eaten plants that produce little,if any,pollen

C.To show that the conclusions that Colinvaux drew from the analysis of pollen in ice-age lake sediments cannot be correct

D.To explain why so-called polar deserts are incapable of supporting such large animals as mammoth,horse,and bison

正確答案：C

題目詳解

題型分類：事實(shí)信息題

原文定位：根據(jù)radiocarbon analysis定位到第五段最后一句

選項(xiàng)分析：

最后一句說Guthrie通過放射性碳的研究來反駁前文Paul Colinvaux的觀點(diǎn)，C選項(xiàng)cannot be correct對(duì)應(yīng)定位句argued against。C選項(xiàng)正確。

A選項(xiàng)，measure the amount of pollen無中生有。

B選項(xiàng)，produce little,if any,pollen無中生有。

D選項(xiàng)，incapable of supporting such large animals與原文the bones date to the period of most intense glaciation（來自最嚴(yán)寒冰期的化石）矛盾。

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