Asteroids necessary assumption question help

LRLang26

Prep test 31 section 3 - Necessary assumption - Asteroids and extinction of dinosaurs

The answers to this question are as follows:
A) any collision of an asteroid with the Earth would have occurred on a land area rather than an ocean
dinosaurs in the neighborhood of an asteroid impact but not within the zone of direct impact would have survived such an impact
C) any event that takes place over a long period of time has many different causes
D) dust from the impact of an asteroid on the Earth would not have had any cooling effect on the climate
E) no more than one large asteroid struck the Earth during the period when the dinosaurs were becoming extinct

Why in AC "D" do we not get to make the assumption that the cooling effect on the climate could lead to the extinction of dinosaurs, but in AC "E" (the correct answer) we are supposed to make the assumption that more asteroid impacts could lead to the requisite amount of dust, rendering the dinosaurs extinct?

Any help on this would be great. Thanks.

gs556

This is one of those questions where the LSAT writers are taking advantage of our biases.

Trent's argument does not address the effects of an asteroid impact, rather only that the Mexican impact couldn't have produced all the dust.

All he's saying is that there's a disconnect between the dust necessary to kill the Dinos and how much dust the Mexican crater could've created. As a test taker this question tricks us into thinking he's arguing about the effects of the crater impact, but he's not.

Once you realize his argument is about the mismatch between the required dust to wipe out the Dinos and the size of the Mexican crater, it is obvious that he assuming that the Mexican impact was the only one. So, if (E) is not true, his argument is wrecked.

LRLang26

Right on. After giving it some thought i started thinking along the lines of what you just said. Thanks for clarifying!