Logical ReasoningDifficulty: Easy

PT5 S1 Q17 Explanation

Sedimentary rock hardens within the

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsWeaken

Keep going in LSAT Lab

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Free to start

Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

Sedimentary rock hardens within the earth’s crust as layers of matter accumulate and the pressure of the layers above converts the layers below into rock. One particular layer of sedimentary rock that contains an unusual amount of the element iridium has been presented as support for a theory that a meteorite collided other matter, and as new layers accumulated above it, it formed a layer of iridium-rich rock.

What this question is testing

Weaken

Your task

Find the choice that makes the argument's conclusion less likely to be true.

Common trap

Answers that look negative but attack a claim the argument never relied on.

Winning move

Find the assumption the argument depends on, then pick the choice that undermines it.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
17.

Which one of the following, if true, would counter the claim that the iridium-rich layer described in the passage is evidence for

Answer choices

  1. No Impact3% picked this

    The huge dust cloud described in the passage would have blocked the transmission of sunlight and

    This doesn't achieve either of our goals: - what else could have caused this layer of iridium rock? - what could ruin the story that a meteorite caused this layer? We can't argue that "since the dust cloud would have cooled off the earth, the dust would not have settled into an iridium layer of rock".

  2. No Impact2% picked this

    A layer of sedimentary rock takes millions of years

    This doesn't achieve either of our goals: - what else could have caused this layer of iridium rock? - what could ruin the story that a meteorite caused this layer? We can't argue that "since the dust would have taken millions of years to harden into rock, this story must be wrong". After all, this collision happened 65 million years ago, so there's plenty of time for those millions of years of hardening to have occurred.

  3. No Impact2% picked this

    Layers of sedimentary rock are used to determine the dates of prehistoric events whether or

    This doesn't achieve either of our goals: - what else could have caused this layer of iridium rock? - what could ruin the story that a meteorite caused this layer? This is just telling us a fun fact about what geologists do with sedimentary rock in their jobs.

  4. Correct91% picked this

    Sixty million years ago there was a surge in volcanic activity in which the matter spewed from the volcanoes

    Why this is right

    This achieves one of our goals: - what else could have caused this layer of iridium rock? - what could ruin the story that a meteorite caused this layer? This provides us with the alternate explanation that the layer of iridium isn't evidence of a meteorite collision; it's evidence of a surge in volcanic activity, which is what supplied the extra helping of iridium.

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

  5. Opposite (if anything)2% picked this

    The iridium deposit occurred at about the same time that many animal species became extinct and some scientists have theorized that mass dinosaur extinctions

    This answer sounds more like it's corroborating the meteorite collision theory, saying "We already believed, for a different reason, that there might have been a meteorite collision around this time period."

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free