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The Earth s rivers constantly carry dissolved salts into its

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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 06 Sep 2012, 00:11
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?

(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 am confused in B and E . Please clarify .
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 26 Jan 2013, 01:01
Level of salt in the ocean = could be use to predict the age of oceans...
How? determining the number of centuries it took to reach current salt-level from less-salt state...

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.
If salt level in the past was also unusually large as now, then perhaps there is no such thing as increase in salt levels that could help determine the age...

(B) At any given time, all the Earth’s rivers have about the same salt levels.
Rivers can have different salt levels and the conclusion will still hold... This is not assumed...

(C) There are salts that leach into the Earth’s oceans directly from the ocean floor.
If there are salts from the ocean floor and salts from river, the comparison of the levels of salt today and past hundred years will still work as an age determinant... TThe conclusion will still hold...

(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
Extreme... There's no claim about the superiority of these method compared to other methods...

(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
Even if salts are used up by the oceans, as long as that consumption rate is the same althroughout.. the method will still work.. This trap is similar to (C) in that it introduces factors other than rivers to contribute to change in salt levels... (e.g. Ocean floor and Biological Process) as long as the salt levels did increase from past to now... then the method will work...

Answer: A
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 24 Sep 2013, 23:56
Option C is a standard trap in an assumption question.

The answer is just the opposite.

The assumption is that salt in ocean is only built through river deposits.

C would've been correct if it were - There are no salts that leach into the ocean directly from the ocean floor.
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 31 Mar 2014, 15:20
Lets see Why It must be A.

Here the issue is about the validity of scale, which is the level of salt, across various time period. And,here,the time period and the consistency of level in that time period only matter. Now all the factors, which are constantly effecting levels across all time periods will not hurt the consistency of salt levels as all these factors are active across the time period consistently.
As far as E is concern, though biological activities effect the level of salt, they do not hurt the consistency of salt levels across the time period ( for instance: they might reduce the level by x% but across all time period so no variation across levels in different time period).

negation of option A will create variation in the salt levels across different time period, creating an error into the method of measuring time period, accurately. Hence will collapse the argument.
Re: The Earth s rivers constantly carry dissolved salts into its   [#permalink] 31 Mar 2014, 15:20
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