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The Earth's rivers constantly carry dissolved salts into its oceans.

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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 21 Oct 2011, 19:37
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A tough one and after much deliberation I choose option A.

To simplify this lets consider that I can walk at a constant rate of 10 km/hr. On a given day I walk 20 kms. It took me 2 hours to cover the distance. The result (time to cover the distance) is depending on the walking rate and not the distance I covered. If I start walking at a higher rate it will take me less time to cover the distance.

Similarly the age of the ocean = Increase in salt level/rate of deposition per century. The assumption is that the rate of deposition is constant; otherwise the result will be inaccurate.

Option A: The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. –this means that the rate of deposition is constant and thus we can accurately calculate the age of the ocean.

Using method of negation
Option E – All (polar opposite of none) of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans. – extreme assumption. Moreover it doesn’t weaken the conclusion as we can still calculate the age of the ocean.

Option A - The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years. – the rate of deposition is not constant. The conclusion falls apart. We can’t accurately calculate the age of the ocean
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 28 Jan 2012, 08:10
Argument concludes the following:
(Inc. in salt levels(caused by the continuous flow of rivers) in the past 100 years) X No. of centuries = Oceans' Accurate age

Two questions that I can think of are;
Q1. What if the increase in salt levels in the past 100 years is different from rest of the centuries? Then, we will not be able to accurately determine the age of the oceans.

2. What if there is another way by which salt levels are increasing?

Let us look at the options now. Our main aim is to keep the relevant and throw out the rest.
(A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. Now, look at Q1. What do you think? This option says that Inc. is unusually large in the past 100 years. BINGO.
(B) At any given time, all the Earth’s rivers have about the same salt levels. We're not talking about ALL the earth's rivers. Too extreme.
(C) There are salts that leach into the Earth’s oceans directly from the ocean floor. Weakens the argument. This says that there are other ways by which salt levels are increasing. This means that Inc. because of the continuous flow of rivers may not be the case.
(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans. Nothing about superiority mentioned. Irrelevant.
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans. Negating this option does not harm the conclusion. Even if salt are used by bio. activity, the value may be constant, still enabling us to find the age.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 16 May 2012, 01:23
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?

(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.



Between A and E.

E is also a strong contender. However, to negate E one will have to make another assumption. (something like: salts have not been used up by biological activities at a constant rate) which goes far from the argument. Hence, A is the best answere dervied through negation technic.

:wink:
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 29 May 2012, 10:55
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. (if it is unusually large, this will not reveal the true age of the oceans)
(B) At any given time, all the Earth’s rivers have about the same salt levels. (Out of scope, salt levels of river do not come into the picture. We are concerned about the salt deposited by these rivers in the oceans)
(C) There are salts that leach into the Earth’s oceans directly from the ocean floor. (out of scope)
(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. (contender. But if we negate A and E, we find A to be stronger)
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 31 May 2012, 01:40
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.


IMO, choice A is the correct one, if the quantities of dissolved salts deposited by rivers in the Earth's oceans have been unusually large during the past hundred years, the estimation will become incorrectly or difficultly to calculate the age of the Earth.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 07 Jun 2012, 02:11
(A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. - Only when it is confirmed there is no unusually large deposits of salt by rivers into the oceans, will we be able to conclude that the age can be calculated precisely. - Correct
(B) At any given time, all the Earth’s rivers have about the same salt levels. - Irrelevant information - No logical outcome for calculation of the age of earth - Incorrect
(C) There are salts that leach into the Earth’s oceans directly from the ocean floor. - Arguement speaks about salts deposited by the rivers - Irrelevant - Incorrect
(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans. - Arguement only mentions about calcluation of earth's age using the salt deposited by rivers. No mention of any other methods - Irrelevant - Incorrect
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans. - If that is the case, then just by calculating the salt deposit by rivers would give us the age of earth. Assuming this does no change to the outcome - Incorrect
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 24 Jun 2012, 06:24
A close call between A and E. I fell for the E trap because if the biological activity uses up the salt the calculations will be inaccurate. But I think the problem is one of extent. In this case, both A and E are assumptions but
In A: if the salts have been unusually high during the past hundred years then there is a greater probability of a more skewed calculation than in a scenario where some salts are being eaten up by the biological activity.

Also if biological activity consumes the salt, there may be a possibility it does so all along. In that case the calculations may not be thrown off. So, there is still a possibility that calculations are accurate. There maybe a uniform offset in the rates due to the biological activity.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 22 Aug 2012, 06:39
I think it is 'E'.
'A' is is talking about the total amount of salt deposited by rivers, not the rate. What does the total amount of salt (be it unusually large or unusually small) have to do with the conclusion? the conclusion is about rate of salt increase, not the total amount deposited during the last hundred years.

The only thing mentioned that can affect the 'rate' of salt increase is the biological consumption mentioned in E.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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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 oceans. [#permalink]

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A will be the correct answer .

E states that the salt is not being used by any biological activity . But , if we are to measure the age of the oceans this will not hamper that measurement as the quantity of salt, if being used by any biological activity would have been constant since the beginning . So , that constant will not affect the measurement .

A assumes that the quantity of salts deposited in recent hundred years is larger than other hundreds of years , thus the experiment will give an inconsistent answer .

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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 31 Mar 2014, 16:20
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.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 25 Apr 2014, 11:53
lexis 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.


Conclusion : By measuring the increase in salt over the past hundred years and by extrapolating the results, we can determine the maximum age of the Earth's Ocean.

Option A) Negation :
The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years.
More quantities of salt is added in the past 100 years, So if we extrapolate it over thousand of years, the years required will be lesser as compared to the actual age. That can impact the Maximum age calculation. Hence an assumption.

Option B) Doesn't matter as argument talks about the cumulative salt in the ocean.
Option C) Salt leach into the Earth's ocean from the floor. This would be captured the data for the last 100 years and it will be constant over the years. Hence it doesn't affect.
Option D) Out of scope.
Option E) Negation.
Some of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
In that case, this would be factored in the measurement done for the past 100 years and can be extrapolated over the thousands of years.

hence A)

BTW : It is from GMATPrep Question Pack 1.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 28 Jan 2015, 23:34
jainshruti64 wrote:
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 .


For anyone else confused about B and E, here's my take on these:

(B) At any given time, all the Earth’s rivers have about the same salt levels.
This talks about salt levels in rivers. I am not sure whether I'm technically right, but I figure salt levels is a per unit calculation. I feel, the salt level alone, without knowing the volume of water, cannot determine the total amount of salt in each river.
Example: River A is 10km long and river B is 50km long. Both have salt levels of 100, but I would think river B has more salt because its larger.
Hence salt levels would have no bearing.
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
Even if some of the salts are used up, E does not say that the people measuring salt levels would be unaware of it. Hence it is possible that the ocean uses 10% of the salt it receives for a certain activity, and the people measuring salt levels already know about it, thus factoring for it in their calculations.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 07 Feb 2015, 07:46
The argument proposes a method of oceans age calculation using the salt levels in oceans.
A - CORRECT.If yes, the method would be wrong to estimate the number of centuries it takes by taking the last century level as a representative amount. If not, the method can be right.
B - OOS. It's not deal with the salt level comparison among all rivers.
C - OOS.
D - OSS.
E - Whether this happens or not, it can be reflected in the ocean's annual salt level.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 09 May 2015, 06:05
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.



Between A and E.
Negate E.
Few of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
Still we can predict age.Only few salts are used,its not "most".
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 05 Jun 2016, 22:41
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.



Let us do it in a speed-time manner.

The author says that we can find the total age (time) of ocean by the rate at which salt is deposited (speed) from the total salt in the ocean (distance)

So time = distance/speed.

Distance ( amount of salt in ocean currently) is a constant.

But what about speed? We need an assumption that caters to " there have been no unusual rate of salt deposition since the beginning... ie; rate has been somewhat constant"

A perfectly does that. If the rate was huge in the last 100 years, the entire hypothesis behind this is destroyed.

Clarifying confusing options :

B At any given time, all the Earth’s rivers have about the same salt levels.

We are talking about the level of salt in the sea, not in the river. Could be that the salt level in river stays the same but due to summer or something the rate at which they deposit goes down and hence there is drop in the rate they are depositing ( Nien)

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

Biological activities must be occurring since a long long time. This is not an anomaly and has no effect on the outcome of the hypothesis
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 12 Sep 2016, 01:46
The whole thing here is to carefully read the premise. Scientists want to estimate the Earth's maximum age. For that they need to find rate in [salt per year] units.
a) Correct. If for the past hundred years the quantities are unusually large, then the rate will be unusually large too -> ruins the estimation
b) Doesn't matter. Even if all rivers have different salt level, scientists estimate the overall effect, not the individual impact
c) Doesn't matter. Scientist take into consideration the overall change, and they don't care how did that change happened.
d) Out of scope
e) Doesn't matter again. Scientists will observe the overall change, and they don't care how did that change happened
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 12 Oct 2016, 02:06
I know this is an old question. I fell for E too but realized why A is correct:

Conclusion: current salt level / salt deposited in the past century.

suppose 1st year salt level was 10, 2nd year an increase of 5, 3rd year an increase of 5, etc. up to the 100th year, i.e. the conclusion is true only when the ratio remains unchanged which implies that there needs to be a constant increase of salt year on year. This is exactly what (A) states and negating A implies that there is no constant increase of salt year on year.

Does my reasoning make sense? Please correct me if I'm wrong. Hope it helps.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 12 Oct 2016, 10:33
jainshruti64 wrote:
I am confused in B and E . Please clarify .

Option B would not be correct because it is not necessary that all the rivers of the earth have about the same salt levels at any given time. They can actually have different salt levels. In other words, it is possible that the salt level of one river is different from the salt level of another river.

When I closely think about it, I believe that possible assumption could have been that rivers have actually been carrying approximately the same “quantity” of salt across centuries. In fact, this is pretty much what option A is saying, and hence is the right answer.

The only other option that comes close to this is option E. However, I believe that this is not the correct option because even if this assumption was false it would mean that rivers are carrying salt along with them to the sea and some of that salt is being consumed by biological activity in the oceans. This is actually ok, because even if that was the case, then for every century, the measured salt quantity increase would actually be a “net” of the salt carried by the rivers into the oceans minus the salt consumed by the biological activity in the oceans. Since this is going to be a uniform pattern all through the history, it would in no way give wrong calculation of the maximum age of the oceans of the earth.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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New post 20 Dec 2016, 23:18
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
* 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


The problem is that the argument clearly does not rely on this assumption. Nowhere in the QS does it mention biological activity. It does, however, mention the method that is being used to estimate the age of the earth
Re: The Earth's rivers constantly carry dissolved salts into its oceans.   [#permalink] 20 Dec 2016, 23:18

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The Earth's rivers constantly carry dissolved salts into its oceans.

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