Nature constantly adjusts the atmospheric carbon level. An increase in the level causes the atmosphere to hold more heat, which causes more water to evaporate from the oceans, which causes increased rain. Rain washes some carbon from the air into the oceans, where it eventually becomes part of the seabed. A decrease in atmospheric carbon causes the atmosphere to hold less heat, which causes decreased evaporation from the oceans, which causes less rain, and thus less carbon is washed into the oceans. Yet some environmentalists worry that burning fossil fuels may raise atmospheric carbon to a dangerous level. It is true that a sustained increase would threaten human life. But the environmentalists should relax-nature will continually adjust the carbon level.
Which one of the following, if true, would most weaken the argument in the passage?
(A) Plant life cannot survive without atmospheric carbon.
(B) It is not clear that breathing excess carbon in the atmosphere will have a negative effect on human life.
(C) Carbon is part of the chemical "blanket" that keeps the Earth warm enough to sustain human life.
(D) Breathing by animals releases almost 30 times as much carbon as does the burning of fossil fuels.
(E) The natural adjustment process, which occurs over millions of years, allows wide fluctuations in the carbon level in the short term.
OA: E
What's the best approach to determine the answer? Can any experts help?
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Nature constantly adjusts the atmospheric carbon level. An i
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BTGmoderatorAT
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No expert, but E is the only logical answer choice here. The argument of the passage is made clear in the last sentence - people should not be concerned about controlling the increase of carbon levels because nature adjusts atmospheric carbon levels continuously. First step is identifying that. Now the question asks you which answer choice weakens the argument the most. Choices A and D have almost nothing to do with the main argument (do not try and control carbon emissions, nature will adjust for it) and choices B and C may actually be seen to strengthen the argument, but they are definitely not countering what's being proposed. By elimination you arrive at answer choice E, which is a clear counter-argument when you examine it. Choice E is saying that the natural adjustment process "allows wide fluctuations in the carbon level in the short term" which would be dangerous, thus the argument of "environmentalists should relax-nature will continually adjust" is weakened by the fact that natural adjustment occurs over millions of years and allows for wide fluctuations in the short term.
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ErikaPrepScholar
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pdutra19's analysis is great! Since this question asks us about the argument of the passage, we should start by clearly defining what the argument of the passage is - this will help us not to get caught up in trap answer choices. Restating the last two sentences of the paragraph gives us: "Nature will adjust the carbon level such that it will not threaten human life." We want to weaken this argument.
A talks about plants. We're really only concerned about human life here. Eliminate.
B indicates that more carbon may not actually hurt human life. If anything, this strengthens the argument - even if the carbon level gets higher, human life won't be threatened. Eliminate.
C indicates that carbon is important for human life. Again, this could be taken to strengthen the argument - more carbon = good for human life. Eliminate.
D indicates that other sources of carbon are more significant than fossil fuels. While the paragraph does mention fossil fuels as something environmentalists are concerned about, they aren't particularly relevant to the argument itself: that nature will adjust the carbon levels, wherever they come from. Eliminate.
E tells us that nature adjusts the carbon levels over a long, long time. This means that the carbon levels can go way way up or way way down during the millions of years, but by the end of that time, it will have leveled out. This means that humans could be exposed to way higher levels of carbon for, say, hundreds of years. If this is the case, it doesn't really matter for human life whether carbon levels level off after millions of years - hundreds of years of much higher carbon levels WILL threaten human life. This weakens the argument that natures adjustment will keep human life from being threatened, so E is the correct answer.
A talks about plants. We're really only concerned about human life here. Eliminate.
B indicates that more carbon may not actually hurt human life. If anything, this strengthens the argument - even if the carbon level gets higher, human life won't be threatened. Eliminate.
C indicates that carbon is important for human life. Again, this could be taken to strengthen the argument - more carbon = good for human life. Eliminate.
D indicates that other sources of carbon are more significant than fossil fuels. While the paragraph does mention fossil fuels as something environmentalists are concerned about, they aren't particularly relevant to the argument itself: that nature will adjust the carbon levels, wherever they come from. Eliminate.
E tells us that nature adjusts the carbon levels over a long, long time. This means that the carbon levels can go way way up or way way down during the millions of years, but by the end of that time, it will have leveled out. This means that humans could be exposed to way higher levels of carbon for, say, hundreds of years. If this is the case, it doesn't really matter for human life whether carbon levels level off after millions of years - hundreds of years of much higher carbon levels WILL threaten human life. This weakens the argument that natures adjustment will keep human life from being threatened, so E is the correct answer.
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