Critical Reasoning

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

The argument is dissolved salts from rivers go into the ocean which incerases ocean salt levels. So calculating rate increase in salt levels will tell us a time when there was no salt in the ocean (perhaps when the Earth was born)

IMO, its E. I used the 'Negation Technique' i.e. take the opposite of E and see its effect on the argument. If E is to be false then the proposed method to calculate Earth's age will not work.

B was another choice but I felt E did the job better.

What is the OA?

I agree with sankruth, It should be E

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.
Out of scope

C. There are salts that leach into the Earth’s oceans directly from the ocean floor.

Weakens not an assumption

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

E. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans

If the determination process is going to take place by measuring the increase in salt for last 100 years then this does not make sense ...because it wont matter

Hence it seems out of scope ..


Hence A

IMO E becoz the argument is based on the assumption that the source of salt is only rivers and also the age can be calculated by the amount of salt increase...if the ocean salt is being used for any biological purpose then the amount of salt in ocean over the past years will not be correct (as calculated against the source...i.e river)..hence E is the assumption.

OA please?

jcmsolis 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

IMO A is the answer, if the quantity of salts put into ocean by the rivers is unusaually large during last century, we can not consistently determine the amount ejected by the rivers previous to this century, hence the argument falls apart

B is pretty good, however, variations in the amount of salt in any particular river over the past is not relevant since they only meassure increase in salt levels in the oceans. How salt was contributed to the oceans' salt increase from any particular river is irrelevant since the final level of salt in the ocean is considered. I still almost chose B, but I think its E. Negation technique helps one arrive at E, I agree.

IMO - E

OA please

A. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Well it doesn't tell if the quantity of salts dissolved was large earlier before either.
So not A

I narrowed down between B and E.

E has a fall out that if the consumption of biological activity is constant throughout( which is not stated), then also we could have determined the age.

But i still go with E.

Whats the OA.

A

in consistency in salt deposition will impact results of analysis....

whts the OA..??

OA ???

I think its E. "A" does say that the salt deposit not been constant therefore might be hard to predict, but the key is that it has been deposited, so you can take it into account. Whereas for E, the assumption that the salt stays there and is not used by an external source is correct.

I'll go with A

If the deposits of salt were unusually high in last hundred years, the calculation of the max age of ocean would not at all be accurate. As author is taking a sample of 100 years data and considering it as a reference, the deposits needs to be comparable and not unusually high.

E states that none of salts is used by biological activity in ocean. Even if it is used up by, thats fine. Say for eg 10% of deposited salt in last 100 years was used up by biological activity. This activity could probably persist earlier also and same 10% percentage would have been used up in earlier years. So 90% of deposited salt amount refers to 100 years. With this data we can still find the max age of ocean.

I will go with A too.

Another vote for E.