Self-study
Scientists analyzing air bubbles that had been trapped in Antarctic ice during the Earth's last ice age found that Support the ice-age atmosphere had contained unusually large amounts of ferrous material and surprisingly small amounts of carbon dioxide. ███ █████████ █████ ████ █████ ██████ ██████ ███████ ████ ███ ███████████ ███ █████████ ████████████ ████ ███ ███████ █████████ █████ ███ █████████ ██ ███████████ █████ ███ ████████ █ █████ ████████ ██ ███ ██████████ ██ █████████ █████ ████ ██ ████████
Summarize Argument: Phenomenon-Hypothesis
The scientist hypothesizes that ferrous material in the atmosphere promoted a great increase in the population of Antarctic algae. This is supported by the observation that air bubbles in ice-age ice had surprisingly high levels of ferrous material and low levels of carbon dioxide. What's more, algae absorb carbon dioxide from the atmosphere.
Notable Assumptions
The scientist assumes that more ferrous material causes more algae. This means assuming that ferrous material has a positive effect on algae growth, and that there isn’t some other cause that’s actually responsible algae growth. The scientist also assumes that algae were actually present in Antarctica at this time, in quantities sufficient to affect the composition of the atmosphere.
4.
Which one of the following, ██ █████ █████ ████ █████████ █████████ ███ ███████████ ███████████
a
Diatoms are a ███████████ ████ ██ █████ ████ ███ ████████ ███████ █████████ █████ ███ ████ ███ ████
This doesn't tell us anything more about the connection between ferrous material and algae. Also, it's not clear how changes or lack of changes to diatoms after the last ice age have any bearing on the population of diatoms during the last ice age.
b
Computer models suggest ████ █ █████ ████████ ██ ███████ ████████ █████ █████ ███████ ███████ ███ ██████ ██ ███████ ██████
If anything, this supports the scientist’s argument by reinforcing the causal connection between ferrous material and algae. We want to weaken this connection, not strengthen it.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).
c
The dust found ██ ███ ███ ███████ ███████ ██ █████████ ███ █████████ █████ ████████ ██ ████████ ██ ███ ███████ █████████
Did these other minerals cause algae growth? Did they have some other effect? We don’t know enough to say whether these minerals are relevant at all, much less whether they weaken the argument.
Failed alternate explanation
Failed alternate explanation
Weaken Qs: Answers that try to introduce an alternate explanation, but fall short, or try to explain a different phenomenon.
Strengthen Qs: Answers that try to eliminate an alternate explanation, but fall short, or try to eliminate an explanation for a different phenomenon.
d
Sediment from the █████ █████ ████ ██████████ ████████ ██ █████████ ██████ ███ ████ ███ ████ ██ ███ ████ ██ █████ ███ ██████ ████ ███████ █████ ████ ████ ███ ████████████
In other words, at least one population of algae didn’t seem to increase at all in Antarctica during the period in question. This suggests the ferrous material wasn’t causing algae growth, thus undermining the argument.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
e
Algae that currently ████ ██ ███ ██████ ████ ██████████ ██ ███ ██████ ██ ██ ██████ ██ ████ █ █████ ████████ ██ ████████ ██ ███████ █████████
Ferrous material doesn't harm algae. This doesn’t weaken the scientist's claim, and in fact defends against a possible problem, that too much ferrous material is harmful to algae.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).