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Suruchim12
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 08 Apr 2022, 05:06
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GMATNinja Why cannot A be the answer?

In order to support the scientists conclusion and that this is a one off case where the hole has diminished, doesnt A solidify that statement - its always increased, up until this year - therefore thats not reason enough to believe that ozone layer is recovering. IMO this is a generalisation argument, isnt it?
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 18 Apr 2022, 11:59
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GMATNinja Why cannot A be the answer?

In order to support the scientists conclusion and that this is a one off case where the hole has diminished, doesnt A solidify that statement - its always increased, up until this year - therefore thats not reason enough to believe that ozone layer is recovering. IMO this is a generalisation argument, isnt it?
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Notice the contradiction at the heart of this passage. On the one hand, it tells us that the ozone hole has "diminished by four million square kilometers" this year compared to the previous year. This suggests that the ozone layer is recovering. Yet for some reason, scientists have not concluded that the ozone layer is recovering.

The question then asks for "the strongest reason for the scientists' reaction to the measurements." So the correct answer should explain why scientists believe the ozone layer is not recovering DESPITE the fact that the hole got smaller.

Let's now consider (A):

Quote:
A. The ozone hole has steadily grown in size every year for the past decade except this year.
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This gives us data about previous years, but it does not explain why scientists believe the ozone layer is not recovering DESPITE the fact that the hole got smaller.

You raise an interesting question: does (A) suggest that this year's data is an outlier and can thus be ignored? That's a pretty big leap to make. Simply because the data is different this year than previous years doesn't necessarily mean it's wrong. Maybe this was the first year the ozone layer started recovering? If so, you wouldn't expect to see any recovery in previous years.

Since (A) doesn't explain why the scientists believe the ozone hole is not recovering despite evidence to the contrary, we can throw it out.

I hope that helps!
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 09 May 2022, 10:42
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CrackverbalGMAT
Pre-thinking:

The scientists have not concluded that the ozone layer is recovering despite the area of the hole in the ozone layer reducing by 4 million sq.km. Patently, this is because the scientists suspect that this could be a temporary or one-off development, possibly caused by factors that are also temporary/one-offs.

We get a hint from the statement that ozone depletion occurs below -78 degrees celsius. Potentially, if there is some temporary/one-off factor which has prevented temperatures falling below -78 degrees celsius this year, it would prevent ozone depletion and could be considered a reason for the scientists' reluctance to declare a recovery of the ozone layer.

Armed with this, let us approach the answer options.

A. The ozone hole has steadily grown in size every year for the past decade except this year. This does not support the scientists' reluctance. If anything, creates the opposite impact. If something has been happening year after year, and suddenly stops, it could be considered a halting of the earlier trend unless an explanation is found for it.

B. The length of time that the ozone hole persists fluctuates from year to year. The stimulus does not give any information about the time for which the hole exists. Therefore, it is unlikely to be a factor in the scientists decision making.

C. As a result of international treaties, CFCs have been completely banned for several years. Since CFCs are a causal factor for depletion, their ban should act as a positive reinforcement for ozone recovery. This does not explain why scientists have not concluded the ozone layer to be in recovery.

D. Weather patterns allowed unusual amounts of warm air to mix into the polar regions this year. Correct answer. Since this year has seen unusual amounts of warm air in the polar regions, it can be expected that the polar regions would have seen higher than usual temperatures. Since ozone depletion occurs only below –78°C, this could be a possible explanation for the scientists' reluctance to conclude that the ozone layer is recovering.

E. Human-made CFCs retain their ability to destroy ozone molecules for seventy-five to one hundred years. There is nothing in the stimulus about the length of time that CFCs are active and how this impacts the ozone. This is not a reason for the scientists' decision.

Hope this helps.
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Why does (B) not provide any information?
If the length of time that hole persists fluctuates, then hole may not exist when scientists measure the hole --> Hole is recovering.
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 13 May 2022, 07:24
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Tanchat

Why does (B) not provide any information?
If the length of time that hole persists fluctuates, then hole may not exist when scientists measure the hole --> Hole is recovering.
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According to the passage, measurements taken this spring show that the ozone hole has diminished by "four million square kilometers" compared to the same time last year. At first glance, this seems to suggest that the ozone layer is recovering. Yet for some reason, scientists have not concluded that the ozone layer is recovering.

The correct answer should provide the "strongest reason" for this reaction. In other words, it should tell us why the scientists don't think the ozone layer is recovering, even though the hole was smaller this spring compared to last spring.

Here's (B) again:

Quote:
Which of the following would, if true, provide the strongest reason for the scientists' reaction to the measurements?

B. The length of time that the ozone hole persists fluctuates from year to year.
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The correct answer should explain why scientists don't believe the ozone layer is recovering DESPITE the fact that the hole was smaller this spring than last spring. Notice that (B) doesn't address the size of the hole. Rather, it tells us about the length of time the hole exists. Since it doesn't directly address the size of the ozone hole, (B) wouldn't explain why scientists think a smaller hole fails to suggest the ozone layer is recovering.

You raise an interesting question in your analysis: what would it mean if the hole did not exist when the scientists measured it? While that's an interesting question, it's not directly relevant to the question. The passage never tells us that scientists took a measurement showing the hole didn't exist. Rather, the scientists found that the hole got smaller compared to the same time last spring.

Since (B) isn't directly relevant to the question, it's incorrect.

I hope that helps!
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 15 May 2022, 03:54
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Tanchat

Why does (B) not provide any information?
If the length of time that hole persists fluctuates, then hole may not exist when scientists measure the hole --> Hole is recovering.
According to the passage, measurements taken this spring show that the ozone hole has diminished by "four million square kilometers" compared to the same time last year. At first glance, this seems to suggest that the ozone layer is recovering. Yet for some reason, scientists have not concluded that the ozone layer is recovering.

The correct answer should provide the "strongest reason" for this reaction. In other words, it should tell us why the scientists don't think the ozone layer is recovering, even though the hole was smaller this spring compared to last spring.

Here's (B) again:

Quote:
Which of the following would, if true, provide the strongest reason for the scientists' reaction to the measurements?

B. The length of time that the ozone hole persists fluctuates from year to year.
The correct answer should explain why scientists don't believe the ozone layer is recovering DESPITE the fact that the hole was smaller this spring than last spring. Notice that (B) doesn't address the size of the hole. Rather, it tells us about the length of time the hole exists. Since it doesn't directly address the size of the ozone hole, (B) wouldn't explain why scientists think a smaller hole fails to suggest the ozone layer is recovering.

You raise an interesting question in your analysis: what would it mean if the hole did not exist when the scientists measured it? While that's an interesting question, it's not directly relevant to the question. The passage never tells us that scientists took a measurement showing the hole didn't exist. Rather, the scientists found that the hole got smaller compared to the same time last spring.

Since (B) isn't directly relevant to the question, it's incorrect.

I hope that helps!
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The correct choice must not only strengthen/weaken the conclusion, but also addressed evidence/premise.

GMATNinja Thank you for your response.
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 29 Oct 2023, 09:13
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GMATIntensive
The Story
Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but chlorofluorocarbons (CFCs) in aerosols and other products have thinned this protective layer. - CFCs in aerosols and other products have thinned the layer of Ozone, which blocks harmful ultraviolet rays from the sun. (We can expect more ultraviolet rays reaching the earth, as a result)

Evidence of this is the ozone hole that forms over the South Pole every Antarctic spring as temperatures drop below –78°C, the temperature at which ozone depletion occurs. - This statement provides evidence for the previous statement that CFCs have thinned the Ozone layer. The evidence is a hole in the ozone layer. The hole forms over the South Pole as temperatures drop below a certain level i.e. - 78°C. This is the temperature at which ozone depletion occurs. (Such low temperature together with CFCs causes depletion of the ozone layer)

Measurements of the ozone hole taken at various times this spring show that, compared with the same times the previous year, its area diminished by four million square kilometers. - This statement suggests that the ozone layer has recovered since the measurements show that the area of the ozone hole has diminished.

Nevertheless, scientists have not concluded that the ozone layer is recovering. - This statement presents a contrast to the previous statement. Even though the measurements suggest that the ozone layer has recovered, scientists have not concluded so.

The Gap
Why do scientists not conclude that the ozone layer is recovering even though the area of the hole has diminished?

Do the scientists believe the measurement taken? If the scientists believe that the measurements are not reliable or understate the size of the hole, they wouldn’t conclude that the ozone layer is recovering.

Was there anything else other than a recovery that could explain the diminished size of the hole? If this year was exceptional in a way that the hole became smaller than it usually would be, then it will be premature to conclude that the ozone layer is recovering.

The Goal
The question stem asks us to find a reason for the scientists' reaction to the measurement. We have already discussed two reasons. Of course, as always, there could be others as well. Just that we were able to come up with two.

The Evaluation
A. The ozone hole has steadily grown in size every year for the past decade except this year.
Incorrect.The option means that the ozone hole has steadily grown for nine years before this year. However, this year, it has diminished. Just because it has grown for nine years before diminishing last year, does it provide a reason to support that the ozone layer is not recovering? No.

Think about it. Whether a person declined in performance for one year or ten years before his performance improved last year shouldn’t help us decide whether the person has improved in the ‘last year’. If his performance has improved, he has improved compared to last year, regardless of his track record before that.

B. The length of time that the ozone hole persists fluctuates from year to year.
Incorrect.What we need to pay attention to here is that this option talks about ‘the length of time’, not ‘the size of the hole’. If this option had stated that the size of the hole fluctuates from year to year, it would have been able to explain why scientists haven’t concluded the recovery of the ozone layer from the diminished size of the hole. If the size of the hole fluctuates from year to year, then this year’s decrease in size of the hole could just be a fluctuation and not an indication of the recovery of the ozone layer.

However, the option talks about ‘the length of time’, which has no impact on the discussion at hand.

C. As a result of international treaties, CFCs have been completely banned for several years.
Incorrect.This option is in the opposite direction. If the CFCs have been completely banned and, as given in the passage, there has been a decrease in the size of the hole in the ozone layer, the scientists should have concluded a recovery. Rather than explaining why scientists have not concluded a recovery, this option gives a reason to conclude that there is a recovery underway.

If the option had stated that CFCs continue to be used as before, then this option could have explained why scientists have not concluded a recovery. Because in such a case, scientists would be wary of concluding a recovery on the basis of certain measurements since they see that the cause of the ozone layer depletion continues to be there.

D. Weather patterns allowed unusual amounts of warm air to mix into the polar regions this year.
Correct.It’s easy to reject this option. It talks about neither the ozone layer nor the CFCs. Thus, if you have a habit of rejecting options just because they mention or do not mention certain words, hard questions are going to remain elusive to you.

One can understand this option only if one pays attention to this part of the passage: “ –78°C, the temperature at which ozone depletion occurs”. For the ozone depletion to occur, temperatures need to be below a certain level. Now, if an ‘unusual’ amount of warm air mixes into the polar regions, the temperatures at the polar regions are going to be higher than usual. Thus, the hole in the ozone layer is going to be smaller than usual, not because the ozone layer is recovering but because of the unusual amounts of warm air. Thus, this option gives us a reason why the scientists have not concluded a recovery of the ozone layer.

E. Human-made CFCs retain their ability to destroy ozone molecules for seventy-five to one hundred years.
Incorrect.Here, some of us may think that since CFCs retain the ability to destroy ozone molecules for a long time, we shouldn’t expect a recovery soon. If we think so, we are overlooking the fact that we have seen a reduction in the size of the hole. If these CFCs retain their ability to destroy the ozone molecules for a long time and there are still the same number of CFCs out there, we shouldn’t expect a reduction in the size of the hole.

However, given that there is a reduction, either there is a decrease in the number of CFCs or there is some other positive factor that helps the ozone layer. In either case, the ozone layer has recovered. So, this option doesn’t give us a reason to explain why scientists have not concluded a recovery of the ozone layer.

SC Notes: The use of ‘this’ in the second sentence of the passage without a noun following it. ‘this’ refers to the entire first sentence. This usage is correct.

If you have any doubts regarding any part of this solution, please feel free to ask.
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GMATIntensive

Can you please explain why is the usage of "THIS" correct here?

Thank you
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 29 Oct 2023, 19:57
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Sonia2023
GMATIntensive

Can you please explain why is the usage of "THIS" correct here?

Thank you
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Hi Sonia2023,

This post may be helpful: usage of this. You may want to solve this official question as well.
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 29 Oct 2023, 20:10
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Another one that I found yesterday - https://gmatclub.com/forum/besides-addi ... 96088.html
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, 05 Nov 2024, 05:59
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Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but chlorofluorocarbons (CFCs) in aerosols and other products have thinned this protective layer. Evidence of this is the ozone hole that forms over the South Pole every Antarctic spring as temperatures drop below –78°C, the temperature at which ozone depletion occurs. Measurements of the ozone hole taken at various times this spring show that, compared with the same times the previous year, its area diminished by four million square kilometers. Nevertheless, scientists have not concluded that the ozone layer is recovering.

A. The ozone hole has steadily grown in size every year for the past decade except this year. -- Eliminate since it's doesn't strengthen the ozone layer is not recovering
B. The length of time that the ozone hole persists fluctuates from year to year. -- Eliminate same reason as A, it doesn't provide any evidence that the layer is not recovering
C. As a result of international treaties, CFCs have been completely banned for several years. -- Eliminate since it's irrelevant to the scientists' reasoning
D. Weather patterns allowed unusual amounts of warm air to mix into the polar regions this year. --Yes since warm air can contribute to the depletion of ozone
E. Human-made CFCs retain their ability to destroy ozone molecules for seventy-five to one hundred years. --Eliminate same reason as C
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