GMAT阅读资料第18篇
To estab***sh such a chronology it is ***cessary *** determ***e the relative amounts of land ***e that exist*** at various ti***s *** the Earth's past. A recent dis***very (10) makes such a determ***ation possible: relative land-***e volu*** f*** a given period can be d***uc*** from the ratio of two o***gen iso***pes, 16 and 18, found *** ocean s***i- ***nts. Almost all the o***gen *** water is o***gen 16, but a few molecules out of every thousand ******rp***ate the (15) he**ier iso***pe 18. When an ***e age beg***s, the ***nti- ***ntal ***e sheets grow, steadily r***uc***g the amount of water evap***at*** from the ocean that will eventually return *** it. Bec***se he**ier iso***pes tend *** be left behid when water evap***ates from the ocean surfaces, (20) the rema******g ocean water be******s progressively enr***h*** *** o***gen 18. The degree of enr***h***nt can be determ****** by analyz***g ocean s***i***nts of the period, bec***se these s***i***nts are ***mpos*** of calcium carbonate shells of mar***e ***ganisms, shells that were (25) ***nstruct*** with o***gen a***ms drawn from the sur- round***g ocean. The higher the ratio of o***gen 18 *** o***gen 16 *** a s***i***ntary speci***n, the m***e land ***e there was when the s***i***nt was laid down.
As an ***d***a***r of shifts *** the Earth's c***mate, the (30) iso***pe re***rd has two advantages. First, it is a global re***rd: there is remarkably ***ttle variation *** iso***pe ratios *** s***i***ntary speci***ns taken from different ***nt***ental locations. Se***nd, it is a m***e ***nt***uous re***rd than that taken from rocks on land. Bec***se of (35) these advantages, s***i***ntary e***dence can be dat*** with suff***ient a***uracy by radio***tr*** ***thods *** estab***sh a precise chronology of the ***e ages. The dat*** iso***pe re***rd ***ws that the fluctuations *** global ***e volu*** over the past several hundr*** thousand years (40) h**e a pattern: an ***e age o***urs roughly once every 100,000 years. These data h**e estab***sh*** a strong ***n***ction between variations *** the Earth's ***bit and the period***ity of the ***e ages.
However, it is imp***tant *** note that other fac***rs, (45) such as volcan*** part***ulates *** variations *** the amount of su***ight receiv*** by the Earth, ***uld potentially h**e affect*** the c***mate. The advantage of the Milanko***tch the***y is that it is testable: changes *** the Earth's ***bit can be calculat*** and dat*** by apply***g New***n's laws (50) of gr**ity *** progressively ear***er ***nfigurations of the bodies *** the solar system. Yet the lack of ***f***mation about other possible fac***rs affect***g global c***mate does not make them unimp***tant.
1. In the passage, the ***th*** is primarily ***terest*** ***
(A) suggest***g an a***ernative *** an outdat*** research ***thod
(B) ***troduc***g a ***w research ***thod that calls an a***ept*** the***y ****** question
(C) emphasiz***g the ***stabi***ty of data gather*** from the app***cation of a ***w scientif*** ***thod
(D) present***g a the***y and describ***g a ***w ***thod *** test that the***y
(E) ***itiat***g a debate about a widely a***ept*** the***y
2. The ***th*** of the passage would be most ***kely *** agree with wh***h of the follow***g state***nts about the Milanko***tch the***y?
(A) It is the o***y possible explanation f*** the ***e ages.
(B) It is ***o ***mit*** *** pro***de a pl***sible explanation f*** the ***e ages, despite recent research f***d***gs.
(C) It cannot be test*** and ***nfir***d until further research on volcan*** acti***ty is do***.
(D) It is o*** pl***sible explanation, though not the o***y o***, f*** the ***e ages.
(E) It is not a pl***sible explanation f*** the ***e ages, a***hough it has ope***d up promis***g possibi***ties f*** future research.
3. It can be ***ferr*** from the passage that the iso***pe re***rd taken from ocean s***i***nts would be less useful *** researchers if wh***h of the follow***g were true?
(A) It ***d***at*** that ***ghter iso***pes of o***gen pr***om***at*** at certa*** ti***s.
(B) It had far m***e gaps *** its sequence than the re***rd taken from rocks on land.
(C) It ***d***at*** that c***mate shifts did not o***ur every 100,000 years.
(D) It ***d***at*** that the ratios of o***gen 16 and o***gen 18 *** ocean water were not ***nsistent with those found *** fresh water.
(E) It stretch*** back f*** o***y a mil***on years.
4. A******d***g *** the passage, wh***h of the follow***g is true of the ratios of o***gen iso***pes *** ocean s***i***nts?
(A) They ***d***ate that s***i***nts found dur***g an ***e age ***nta*** m***e calcium carbonate than s***i***nts f******d at other ti***s.
(B) They are less re***able than the e***dence from rocks on land *** determ******g the volu*** of land ***e.
(C) They can be us*** *** d***uce the relative volu*** of land ***e that was present when the s***i***nt was laid down.
(D) They are m***e unpr******table dur***g an ***e age than *** other c***mat*** ***nditions.
(E) They can be us*** *** determ***e atmospher*** ***nditions at various ti***s *** the past.
5. It can be ***ferr*** from the passage that precipitation f******d from evap***at*** ocean water has
(A) the sa*** iso***p*** ratio as ocean water
(B) less o***gen 18 than does ocean water
(C) less o***gen 18 than has the ***e ***nta****** *** ***nt***ental ***e sheets
(D) a different iso***p*** ***mpo***ion than has precipitation f******d from water on land
(E) m***e o***gen 16 than has precipitation f******d from fresh water
6. A******d***g *** the passage, wh***h of the follow***g is (are) true of the ***e ages?
Ⅰ. The last ***e age o***urr*** about 25,000 years a***.
Ⅱ. Ice ages h**e last*** about 10,000 years f*** at least the last several hundr*** thousand years.
Ⅲ. Ice ages h**e o***urr*** about every 100,000 years f*** at least the last several hundr*** thousand years.
(A) Ⅰ o***y
(B) Ⅱ o***y
(C) Ⅲ o***y
(D) Ⅰand o***y
(E) Ⅰ,Ⅱ and Ⅲ
7. It can be ***ferr*** from the passage that calcium carbonate shells
(A) are not as susceptible *** deteri***ation as rocks
(B) are less ***mmon *** s***i***nts f******d dur***g an ***e age
(C) are found o***y *** areas that were once ***ver*** by land ***e
(D) ***nta*** radioactive material that can be us*** *** determ***e a s***i***nt's iso***p*** ***mpo***ion
(E) reflect the iso***p*** ***mpo***ion of the water at the ti*** the shells were f******d
8. The purpose of the last paragraph of the passage is ***
(A) offer a note of c***tion
(B) ***troduce ***w e***dence
(C) present two recent dis***veries
(D) summarize material *** the prec******g paragraphs
(E) offer two explanations f*** a pheno***non
9. A******d***g *** the passage, o*** advantage of study***g the iso***pe re***rd of ocean s***i***nts is that it
(A) ***rresponds with the re***rd of ***e volu*** taken from rocks on land
(B) ***ws ***ttle variation *** iso***pe ratios when samples are taken from different ***nt***ental locations
(C) ***rresponds with pr******tions already made by c***ma***logists and experts *** other fields
(D) ***nfirms the re***rd of ***e volu*** ***itially estab***sh*** by analyz***g variations *** volcan*** emissions
(E) pro***des data that can be us*** *** substantiate re***rds ***ncern***g variations *** the amount of su***ight receiv*** by the Earth
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