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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]

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20 Dec 2007, 16:47
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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.
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20 Dec 2007, 16:59
A. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. it has to be same all the time, not only recent years
B. At any given time, all the Earth’s rivers have about the same salt levels. Required assumption
C. There are salts that leach into the Earth’s oceans directly from the ocean floor. unrelated
D. There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans. unrelated
E. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans. age can still be determined if biological activity consumes same amount every year of salt so wrong assumption

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20 Dec 2007, 19:24
The following seem to be the assumptions:

1. The deposited salts are not used by any other activity (option E)
2. The salt deposited by various rivers into the ocean at different times in history can be estimated. This is different from option B which states that all rivers carry same salts at a given time.

Whats the OA?
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Re: CR - ocean Salt [#permalink]

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20 Dec 2007, 19:24
gregspirited 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.

Will go for 'E'..
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24 Dec 2007, 04:50
Also E. Finally, the argument depends on not the salt levels in the rivers but the salt level in the ocean.
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24 Dec 2007, 19:43
Chose B as well.
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Re: CR - ocean Salt [#permalink]

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25 Dec 2007, 03:02
A states that the amount of salt rivers deposit into the oceans remains constant, so the age of oceans could be easily detected. B is actually interesting but, after all, we do not care for the amount of salt in the rivers...we care for the amount deposited in the oceans. E refers to the possibility that the amount of salt could change if biological activity takes place....but it refers only to recent times..even though I am the only one..in my opinion A is correct. what's OA?
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25 Dec 2007, 03:30
E.
according to the assumption, no salt is consumed by any biological activitiy in the ocean so all the salt brought in by rivers is available which would provide a correct estimate of ocean's age.
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29 Dec 2007, 15:21
I considered E but discarded it for the following reason: we are given no reason not to think that such biological activity wouldnt have been occuring since the birth of earth's oceans. thus we'd still be comparing apples with apples when measuring the increase in salt levels and then extrapolating back in time.

HOWEVER with A: we are assuming that what we now measure is identical to past performance, which was NOT measured. if the rate of salt increase has increased dramatically, WE WONT KNOW and thus our measurements will be wrong.

A.
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Re: CR - ocean Salt [#permalink]

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03 Jan 2008, 23:34
I am pretty sure it's B

We are assuming the salt levels are increasing constantly over the earths age, so we can use the sample of the last 100 years. If at any point the Earth had lets say for example 90% of its salt deposited at one time in the past in one instance , you wouldnt be able to estimate the age of the earth by just using the increase in salt over the last 100 years. If you assume that the levels of salt were entering the river were constant then u can accurately predict using the last 100 years as a sample.

E is wrong because just because a fish uses salt in its biological process doesnt mean the salt ever leaves the ocean...maybe a fish uses it and excretes it, it's still in the ocean.
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Re: CR - ocean Salt [#permalink]

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04 Jan 2008, 11:40
I will go for 'B'.

B and E are close.

To have an accurate estimates of age, we have to make sure that the rivers have the uniform level of salt at any time. so 'B' is correct.

E does not talk about the uniform level of salt in river water.
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Re: CR - ocean Salt [#permalink]

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04 Jan 2008, 12:02
i think its time for OA.
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Re: CR - ocean Salt [#permalink]

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04 Jan 2008, 18:38
I am a newbi

I think D should be OA

You negate D, you will see D will weaken the argument.
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Re: CR - ocean Salt   [#permalink] 04 Jan 2008, 18:38
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