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# The Earth s rivers constantly carry dissolved salts into its

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The Earth s rivers constantly carry dissolved salts into its [#permalink]  14 Aug 2008, 22:45
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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.
[Reveal] Spoiler: OA
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Re: CR Salt content [#permalink]  15 Aug 2008, 00:23
hibloom 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?

* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
* At any given time, all the Earth’s rivers have about the same salt levels.
* There are salts that leach into the Earth’s oceans directly from the ocean floor.
* There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
* None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

Between A & E.

I am more inclined towards A though, but confusing.
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Re: CR Salt content [#permalink]  15 Aug 2008, 04:11
ill say E. Without E, the authors method wont work since he relies on none of the salt being used up .... if it were, the age would be inaccurate
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Re: CR Salt content [#permalink]  15 Aug 2008, 06:06
IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result
* At any given time, all the Earth’s rivers have about the same salt levels.
OOS
* There are salts that leach into the Earth’s oceans directly from the ocean floor.
OOS
* There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
OOS
* None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
If biological process uses the same salt, concentration will definitely fall
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Re: CR Salt content [#permalink]  15 Aug 2008, 11:33
hey alpha y dont you share your line of reasoning
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Re: CR Salt content [#permalink]  15 Aug 2008, 17:17
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Conclusion: the maximum age of the Earth’s oceans = (Current Salt Level - hypothetical initial salt-free state) / (the oceans over the past hundred years)

Assumption: For every year there is constant salt deposit in the ocean. If not, this argument falls apart.

B
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Re: CR Salt content [#permalink]  15 Aug 2008, 18:24
Only B & E makes sense

B : only if the salt content carried by the river is constant, will the calculation of salt content in the ocean be possible.

E : this seems to more directly implied than the previous one.

Hence I would go with E

Whats the OA??
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Re: CR Salt content [#permalink]  15 Aug 2008, 18:37
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priyankur_saha@ml.com wrote:
IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result

If the quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years , it will surely affect the result.

Consider the salts deposited in the past century is X.

The current salt level is say 5X

so as per the result ocean's age is 5 centuries.

But if X is unusually large and the deposited salt level of previous centuries were say only X/4 per century then the result will have a blunder!
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Re: CR Salt content [#permalink]  15 Aug 2008, 21:05
alpha_plus_gamma wrote:
priyankur_saha@ml.com wrote:
IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result

If the quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years , it will surely affect the result.

Consider the salts deposited in the past century is X.

The current salt level is say 5X

so as per the result ocean's age is 5 centuries.

But if X is unusually large and the deposited salt level of previous centuries were say only X/4 per century then the result will have a blunder!

I'm confused between A and E, but I think A is the best. Partly I agree with alpha_plus_gamma, partly I think E is too an extreme assumption
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Re: CR Salt content [#permalink]  15 Aug 2008, 21:14
OA is A
nice explanation by alpha
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Re: CR Salt content [#permalink]  15 Aug 2008, 21:23
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between A and E...
one of the best ways for CR assumption questions
negate the assumption and the argument should fall apart.

negate E
Some of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
OK.. but if the portion of salt consumed by biological activities has remained constant over the years ... we can still predict the age of the oceans ... the argument doesnt fall apart

negate A
The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years.
it means that the rate has not been constant .... we cant predict the age .... agrument falls apart ...

right Option A
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Re: CR Salt content [#permalink]  05 Oct 2010, 04:08
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+1 for OA.

Have not been large is same as constant.. i.e. over the last 100 years the the amount of salt dissolving into sea is constant
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Re: CR Salt content [#permalink]  05 Oct 2010, 06:10
alpha_plus_gamma wrote:
priyankur_saha@ml.com wrote:
IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result

If the quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years , it will surely affect the result.

Consider the salts deposited in the past century is X.

The current salt level is say 5X

so as per the result ocean's age is 5 centuries.

But if X is unusually large and the deposited salt level of previous centuries were say only X/4 per century then the result will have a blunder!

the problem says "...from a hypothetical initial salt-free state..."

in every century, there could be an increase and this increase should be roughly constant, then we could calculate the result. if portion of the salt was used in other way, ie. not calculated, then the result cannot be produced.

imo, E.
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Re: CR Salt content [#permalink]  05 Oct 2010, 07:29
hibloom wrote:
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.

i was a difficult choice between a and e.
I eliminated E with the foll. reasoning.
If at the beginning of the last century,the ocean contained x kgs of salt.
If in the last 100 years , 100 kgs of ice was dropped into the ocean by the rivers.
and suppose that in the past 100 yrs 5 kgs of salt was used up by the ocean because of its biological activity.
then 95 kgs was dropped in the last century.
So the level becomes x + 95
still we can find out the age of the ocean by taking 95 kgs as the average increase in 1 century.
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Re: CR Salt content [#permalink]  05 Oct 2010, 09:02
Got it right.Good One thanks.
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Re: CR Salt content [#permalink]  05 Oct 2010, 09:09
ankitranjan wrote:
Got it right.Good One thanks.

u can add value to this forum by explaining.This forum is for give as well as take.
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Re: CR Salt content [#permalink]  05 Oct 2010, 09:11
A
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Re: CR Salt content [#permalink]  05 Oct 2010, 18:24
I initially had a strong urge to choose E after I narrowed down A and E.

However after some time thought option E could be broken but not A. Here is why:

Option E talks about "none of the salt getting used up". By taking the resulting increase in salt levels in the oceans over the past hundred years we could accommodate the the condition wherein some of the salt is being used up.

Hence option E is not the safe assumption to make. Hence A is the answer.
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Re: CR Salt content [#permalink]  05 Oct 2010, 19:10
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Has to be A as biological activity will happen every year.

So if rivers bring salt S and biological consumption is s then for a year the Salt increase would be S-s.
So even if we look at a long period every year s amount of salt gets consumed by biological consumption.
That way we can calculate the no of years based on X/(S-s) where X is total increase in the Salt content. So biological activity should not be a problem.

Thanks
Arun
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Re: CR Salt content [#permalink]  05 Oct 2010, 21:30
C and D are out .
From A, B and E
I chose E.
For A-it is not about large quantities or small quantities.
For B-We are concerned about the total salt content of all rivers to be same not independent rivers.
For E-it is a perfect answer.
Furthermore if you negate E.conclusion weakens that we may not get the true age.

Please let me know if i am correct
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Re: CR Salt content   [#permalink] 05 Oct 2010, 21:30

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