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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?
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.
Option A is the correct answer.
Question type : Find the assumption.
Summary of the argument: The argument says that the age of the oceans can be estimated by estimating the amount of salt that is being carried into it by the rivers from a hypothetical salt-free state.
A) Correct Answer
B) It doesn’t matter if each individual river has the same amount of salt as the argument is concerned about the cumulative amount of salt in the ocean.
C) This weakens the argument. If there are salts that come from other sources then the age of the oceans cannot be determined.
D) A good contender. However, this is a very generic answer choice and doesn’t talk about the methodology of determining the age of the ocean.
E) We are not concerned about the salt consumed by the biological activity.