jainrahul1985 wrote:The Earth's rivers constantly carry dissolved salts into its oceans. Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth's oceans can be accurately estimated.
Which of the following is an assumption on which the argument depends?
A.The quantities of dissolved salts deposited by rivers in the Earth's oceans have not been unusually large during the past hundred years.
B.At any given time, all the Earth's rivers have about the same salt levels.
C.There are salts that leach into the Earth's oceans directly from the ocean floor.
D.There is no method superior to that based on salt levels for estimating the maximum age of the Earth's oceans.
E.None of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans.
Confused b/w
A and E . Please suggest
Conclusion: We can count the increases in salt levels in order to determine the age of the earth.
Premise: Rivers deposit dissolved salt into the oceans.
Assumption: That we can use the salt levels to determine the maximum age of the earth's oceans.
The assumption is the answer choice that
must be true in order for the conclusion to remain valid.
A.The quantities of dissolved salts deposited by rivers in the Earth's oceans have not been unusually large during the past hundred years.
Correct. The argument assumes that we can use data from the past hundred years to make deductions about the previous centuries. If the quantities over the past 100 years have been unusually large, we can't use them to learn about the previous centuries.
B.At any given time, all the Earth's rivers have about the same salt levels.
No. Every river does not have to hold the same amount of salt in order for us to determine the age of the earth's oceans.
C.There are salts that leach into the Earth's oceans directly from the ocean floor.
No. This answer choice would weaken the conclusion. The assumption should help the conclusion by connecting it to the premise.
D.There is no method superior to that based on salt levels for estimating the maximum age of the Earth's oceans.
Out of scope. The argument does not claim that the salt-level method is better than any other method.
E.None of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans.
Too extreme. Even if some of the salts are used up, the amount could be so small that we could still use the salt levels to determine the age of the earth's oceans.
[Please note that my thoughts about A and E have been edited -- post-caffeine -- as per the discussion below.]
Last edited by
GMATGuruNY on Sun Sep 12, 2010 7:10 am, edited 2 times in total.
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