Professor Robinson: A large meteorite

Answer choices

1. A

   Correct61% picked this

   The crater indicates an impact of more than sufficient size to have caused

   Why this is right

   The author doesn't need to assume that the crater was big enough to have caused the mass extinction. He's arguing that the meteorite didn't cause the mass extinction. This answer would actually weaken the author's argument, so he wouldn't be assuming it.

   Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

   61%
2. B

   Assumed9% picked this

   The recovered rocks recrystallized shortly after

   If the recovered rocks didn't recrystallize for a long time after they melted, then that creates a possible timeline like this: Meteorite hits during a time of reversed polarity and causes the mass extinction. The rocks recrystallize much later, by which point Earth has already switched back to normal polarity. That's why they show mismatching polarity.

   9%
3. C

   Assumed10% picked this

   No other event caused the rocks to melt after the impact

   If some other event caused the rocks to melt, after the meteorite impact, then that creates a possible timeline like this: Meteorite hits during a time of reversed polarity and causes the mass extinction. At that point, the rocks would have reversed polarity. But then, some other event later causes the rocks to melt. By that point, Earth has already switched back to normal polarity. So when the rocks recrystallize after that later melting, they end up with normal polarity.

   10%
4. D

   Assumed7% picked this

   The recovered rocks melted as a result of the impact that

   If the recovered rocks didn't melt as a result of the meteorite impact, then looking at the rocks' polarity as a timestamp for when the meteorite hit would no longer make any sense. This negation would allow for the rocks to have melted and recrystallized during some period of normal polarity (could be before the impact or after, doesn't really matter). This means the meteorite could have impacted during reverse polarity, and caused the mass extinction. And the rocks don't have that reverse polarity "fingerprint", because they didn't actually melt and re-crystallize from that event.

   7%
5. E

   Assumed12% picked this

   The mass extinction would have occurred soon after the impact that

   If the mass extinction didn't occur for long after the impact, then that creates a possible timeline like this: Meteorite hits during a time of normal polarity and causes the rocks to have that normal polarity "fingerprint". The mass extinction caused by the meteorite impact takes a long time to develop, and by that point Earth has switched back to reverse polarity. That's why the rocks have different polarity from the polarity that occurred during the extinction.

   12%