Logical Reasoning

PT149 · S4 · Q4 It has been hypothesized

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It has been hypothesized that our solar system was formed from a cloud of gas and dust produced by a supernova — an especially powerful explosion of a star.

Conclusion (thereby)

The hypothesis is disproved.

rephrase: Our solar system was not formed from a cloud of gas and dust produced by a supernova.

Intermediate Conclusion (so)

If our solar system were formed from the remnants of a supernova, then iron-60 would have been present in the early history of the solar system.

Evidence

Supernovas produce the isotope iron-60.

But researchers have found no iron-60 in meteorites that formed early in the solar system's history.

Evaluate

The author's argument is structured as a Rebuttal that uses Contrapositive Logic to defeat the conclusion, by showing that a certain implication of the conclusion does not follow. Here is that structure:

- Some people say X. - But if X were true, Y would be true. - Y isn't true. - Thus, X isn't true.

In this case, the argument is like this: - Some people say [solar system from supernova] - If [solar system from supernova] were true, then [iron-60 in early history] would be true. - but [iron-60 in early history isn't true]. - Thus, [solar system from supernova] not true.

The author failed to establish that 3rd claim.

We need to hear that to trigger that contrapositive.

She only told us that, .

Goal

So a Linking idea being assumed is that,

iron-60 wasn't found → iron-60 wasn't present in early meteorites in early solar system

Or by contrapositive,

iron-60 was present → iron-60 would be present in early solar system in early meteorites

The author is also assuming Defender ideas like there are not other places we should look for iron-60 besides meteorites / we will not eventually find iron-60 inside an early meteorite / the iron-60 that was once in these meteorites has not decayed away

Which one of the following is an assumption required by the argument?

If a meteorite is formed
Opposite: unlikely
The author is thinking that a meteorite from around the time of the early solar system would be likely (if not certain) to contain chemical elements (such as iron-60) that were present in the supernova.
3% picked this
Other solar systems are not
Out of Scope: other solar systems
This argument is only about the story of our solar system, so the author doesn't need to assume anything about what goes on elsewhere.
1% picked this
Supernovas do not produce significant
Trap
Negation Doesn't Weaken Only Thing Mentioned ≠ Only Thing Tons of correct answers on Necessary Assumption are written in a ruling-out "not" style, so we can negate this and see if it weakens. Would it hurt the argument to say that, "Supernovas do produce significant quantities of other forms of iron as well"? No, that does nothing. The author's argument could also work by saying, "Supernovas also produce iron-45, but there's no iron-45 in meteorites either", but that's not any objection to the argument the author is making. This answer is doing the classic Necessary Assumption trap of acting like "since the argument only mentioned iron-60, they must be assuming that iron-60 is the only type of iron we care about". We can never assume that because an author chooses to say "Y is true of X" that he's assuming that X is the only thing / the most important thing for which Y is true.
5% picked this
Researchers have found iron-60 in
Out of Scope: late history
The author's argument has nothing to do with later in the solar system's history. She doesn't really care whether iron-60 meteorites were or weren't found later. She is simply saying, since they weren't found early, that proves that the solar system wasn't created from a supernova's debris.
2% picked this
Correct
If there had been iron-60
Why this is right
This shows us the Linking move we predicted, but in contrapositive form (as most correct answers on Assumption like to do, in order to better "hide" its correctness). We knew that the argument fell short of establishing the contrapositive trigger that "iron-60 was not present in the early history of the solar system" because all it told us was "iron-60 wasn't found in meteorites in the early solar system". The author was assuming that link of, "If we didn't find it meteorites, then it wasn't in the early solar system". And by contrapositive, "If it was in the early solar system, then we would find it in meteorites." Generally, it's unwise to negate conditional answers, but if we're negating (if X, then Y), we're getting "it's possible that X is true and Y isn't". So the negation here is, "It's possible that there was iron-60 in the early solar system, but not iron-60 in meteorites."
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
89% picked this

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