Logical Reasoning

PT5 · S1 · Q17 Sedimentary rock hardens within the

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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.

Curious Fact

Why is there a layer of iridium-rich rock?

Geologists' Explanation

A meteorite, which is rich in iridium, collided with earth. That collision raised an iridium-rich cloud of dust, which then settled to the ground and new layers accumulated on top, flattening it in to this iridium-rich rock layer.

Goal

Our task here is weird. We're supposed to find an answer that helps us say, .

So we probably need to do one of our two classic moves when we're dealing with Explain Curious Fact type situations:

- suggest an alternate explanation for the curious fact what else could have caused this layer of iridium rock?

- make the author's explanation seem less plausible what could ruin the story that a meteorite caused this layer?

17.

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

The huge dust cloud described
No Impact
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".
3% picked this
A layer of sedimentary rock
No Impact
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.
2% picked this
Layers of sedimentary rock are
No Impact
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.
2% picked this
Correct
Sixty million years ago there
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.
91% picked this
The iridium deposit occurred at
Opposite (if anything)
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."
2% picked this

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