# In the troposphere, the lowest level of the earth's atmosphere, the temperature decreases as one progresses straight ...

kens on May 11, 2020

question 18

Can you elaborate more on this question? Thanks

Victoria on May 11, 2020

Hi @kenken,

Happy to help!

This is a "must be true" question. We are looking for the answer choice which must be true based on the stimulus

This stimulus is a collection of facts. We are looking for the answer choice which is supported by the facts presented in the passage.

What does the passage tell us?

1) The troposphere (T) is the lowest level of the earth's atmosphere.
2) As you move upward in T, the temperature decreases.
3) At the top of layer T, the temperature ranges from -50 over the poles to -85 over the equator.
4) The next layer after T is called the stratosphere (S).
5) As you move upward in S, the temperature increases.
6) S is warmed by ozone which generates heat when it absorbs ultraviolet sunlight.

Now that we have an understanding of what the passage is telling us, let's go through the answer choices.

Answer choice (A) is incorrect because there is no information in the passage to support this. We are not provided with any information on the thickness of the layers.

Answer choice (B) is incorrect because there is not enough information to support this. We know that it is warmer over the poles than over the equator in T. This does not mean that we can conclude the same about S.

Answer choice (C) is incorrect because there is not enough information to support this. We are not provided with any information on the varying temperatures at different levels/regions of the S layer.

Answer choice (E) is incorrect because the opposite is suggested by the passage. We know that S is warmed by ozone. Therefore, it would make sense that if the amount of ozone surrounding the earth was depleted, the temperature of S would decrease.

Now let's look at (D). We know that directly above the top of T, the S layer begins and that the temperature increases as you move upwards in S.

Therefore, it follows that the temperature at the top of S would be at least as great as the temperature at the top of T directly beneath it because the temperature increases as you move upwards in S. While it follows that the temperature would therefore likely be greater, we can definitively conclude that the temperature would be at least as great as the top of T based on the information we are provided with.

Hope this is helpful! Please let us know if you have any further questions.