Logical Reasoning

PT151 · S2 · Q16 Scientist: An orbiting spacecraft detected

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Scientist: An orbiting spacecraft detected a short-term spike in sulfur dioxide in Venus’s atmosphere.

Conclusion

We shouldn't conclude that volcanic activity caused the sulfur dioxide spike on Venus.

Evidence

No active volcanoes have been identified on Venus, and the sulfur dioxide spike may just be from a cyclical variation in the chemical composition of Venus's planetary atmosphere (planets are known to have variations).

Evaluation

If we want to argue that the spike in sulfur dioxide is caused by volcanoes, we have a couple possible ways to weaken:

- we can make it seem like "cyclical variations" is unlikely to be the cause of what we saw. Maybe cyclical variations are known to happen, but they don't spike as dramatically or change as quickly as what we just saw from Venus's short-term spike.

- we can try to address the "no active volcanoes have been identified" premise, maybe by arguing in an Unproven vs. Proven False style that . Maybe we've only ever seen one side of Venus, so there might be active volcanoes "hiding" on part of Venus's surface that we can't get a good look at.

Goal

Look for something undermining the alternate explanation that it's just a cyclical change in Venus's atmosphere, or for something defending the possibility that it might be volcanoes that are the cause.

16.

Which one of the following, if true, most weakens the scientist's argument?

  1. Correct

    Conditions on Venus make it

    Why this is right

    This answer responds to the first premise, diluting its logical force. AUTHOR: we can't conclude this spike of sulfur is from volcanoes US: yes, we can. It's from volcanoes! AUTHOR: Oh yeah, then how come no active volcanoes have been identified on Venus? US: Because we can't identify them, not because they aren't there. It would be hard for any instrument on Earth to detect a volcano there, given the conditions on the planet (Venus's atmosphere is a thick fog of noxious chemicals). This is saying that even if there are active volcanoes, we are unlikely to be able to directly perceive it. So a lack of direct evidence for active volcanoes isn't really conclusive in terms of whether or not there are active volcanoes there. It's almost like if the argument were, "Bruce's fingerprints weren't at the crime scene, so Bruce didn't commit the crime", and this answer is saying, "Well, given the conditions at the crime scene, we would have been very unlikely to find fingerprints no matter what instrument we used to hunt for them."

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

    66% picked this

  2. Evidence suggests that there was

    Opposite

    This somewhat strengthens the author's hypothesis that sulfur dioxide spikes are cyclical variations.

    4% picked this

  3. Levels of sulfur dioxide have

    Out of Scope Comparison

    We don't care how Venus's sulfur dioxide levels compare to Earth's. We're only interested in why Venus's current levels are higher than Venus's recent levels.

    4% picked this

  4. Traces of the sulfur dioxide

    No Impact / Thin Ice

    We might try to use this to say, "Sure, author, I know you haven't identified any active volcanoes on Venus, but you know there were active volcanoes in the past, so maybe the short term spike of sulfur we just observed is from one of those past volcanoes! (After all, that sorta thing happens on Earth.) But there are a couple problems with that storyline: (1) the idea of an active vs. dormant volcano is something that plays out over geologic time scales, like a volcano is active if it's erupted in the last 10,000 years. So when the author is saying, "we haven't identified any active volcanos on Venus", she's saying we don't know of any volcano that's erupted in thousands of years. This answer is talking about traces lingering "for years", but most people would interpret that somewhere in the 5-100 range, not in thousands of years. So we can't argue our way around "no active volcanoes" by saying, "I know there aren't currently, but a few years ago there were, so maybe this sulfur spike is leftover from that." If there are no active volcanoes, then there haven't been any eruptions for thousands of years. (2) The answer is about 'traces of sulfur' not a 'spike'. A spike is when something goes up. A trace is a measurable amount, but traces exist even as something is lessening in concentration. When you have an eruption, there is a spike in atmospheric sulfur (the level of sulfur goes up). Then slowly over many years the sulfur will disperse throughout the atmosphere and start to dissipate. But there will still be measurable traces that whole time. So you could observe TRACES years after a volcano, but you wouldn't observe a short-term spike (a quick increase) in sulfur years after a volcano.

    24% picked this

  5. Most instances of sulfur dioxide

    No Impact / Opposite

    Since we don't think there are aliens on Venus who are burning fossil fuels, this has no real relevance to analyzing what's going on with Venus. However, if anything, it would suggest that the most common source of a sulfur dioxide spike is not volcanic activity, so that would support the author's conclusion.

    2% picked this

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