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TOEFL Reading: Inference question, K-T event

 

TOEFL reading inference question

  1. The microscopic meteoritic Ir deposition takes 1 mil years.

  2. The Ir deposition of the boundary clay did not take 1 mil years

  3. Therefore, the Ir deposition of the boundary clay could not have come from microscopic meteorites   


The argument employs Modus Tollens: 

  1. P → Q (If microscopic meteorites → Ir deposition takes 1 mil years).

  2. Not Q (not 1 mil)

  3. Therefore, Not P (not microscopic meteorites)


So, you need to look for a choice that is consistent with 3, which is that the  situation was not normal in the case of the Ir deposition of the boundary clay.


  1. the Ir in microscopic meteorites reaching Earth during the Cretaceous period would have been incorporated into Earth’s core

  2. the Ir in the boundary clay was deposited much more than a million years ago

  3. the concentration of Ir in the boundary clay is higher than in microscopic meteorites

  4. the amount of Ir in the boundary clay is too great to have come from microscopic meteorites during the time the boundary clay was deposited

 

A: Not possible. Meteoritic Ir only stays on the surface of the earth. The Ir in the earth’s core is intrinsic to the earth and incorporated into Earth’s core when the earth was formed (Hint: first sentence) 


B is not mentioned


C is a trap as you can misread it. The amount (not the concentration) of Ir in the boundary clay is higher than in microscopic meteorites. Also C does not relate to 3.


D is what 3 is saying, so D is what we are looking for.



TOEFL reading