Self-study
On the basis of the available evidence, Antarctica has generally been thought to have been covered by ice for at least the past 14 million years. █████████ ████████ ██████████████████████ ███████ ██ █ ████ ██████████ █████ ████ ██ ███████████ █████████ ████ ██████████ █████ ███ ███ █████ ████████ ███████ ███████████ █████ █████ ███████ █████ ████ ██████████ ███ █████████ ███ █████ ████ ███████████ ████ ███████ █████ ████ ██████ ██████ ████████ ███████ ██ ████████ ████████ ██ ████████████ █████████ █████ ████ ██████ ███ ███ ██████ ████ ███████ ███ ██████ ███ ██████████ ███ ██████████
Stimulus Summary
For a long time, scientists thought Antarctica had been ice-covered for at least 14 million years. Then they found three-million-year-old fossils under the ice in central Antarctica, of a kind that had only ever shown up in ocean-floor sediments before. The author concludes that the ice sheet must have briefly melted about three million years ago.
The thinking goes: these fossils have only been seen in ocean-floor mud, so central Antarctica must once have been ocean floor, which means the ice melted and the sea rose high enough to submerge the continent. The "after all" sentence backs this up by naming two things that could have melted the ice, severe warming or volcanic activity.
The author assumes the only way these fossils could be there is if the spot had been ocean floor, ignoring other ways they might have arrived. And the support only says warming or volcanic activity could have melted the ice, which shows melting was possible, not that it actually happened.
17.
The reasoning in the argument ██ ████ ██████████ ██ █████ ███ ██ ███ █████████ ███████████
a
That a given ████████ ██ ██████ ████████ ██ ██ ████ ██ █████ ██ ████ ████ ███ ████████ ██ ████████ █████ ██ █████ ██ █████
The author’s conclusion that the ice sheet must have melted is not based on the idea that this view is widely believed to be true. We don’t know whether other people besides the author believe the ice sheet melted.
b
That either of ███ ██████ █████ █████████████ ████ ████████ █ █████ ██████ ██ █████ ██ ████ ████ █████ ███ ██████ █████ ███ ████ ████████ ██ ███████████ ██ ███████ ████ ███████
The author does not assume that the melting of the ice sheet could not have been produced by a combination of climatic warming and volcanic activity. The author presents those two things as potential causes for the melting, but never suggests they were mutually exclusive.
c
Establishing that a ███████ █████ ████████ ██ ████████ ████ ██████ ███████████ ███ █████ ██ ████ ██████
This gets the structure backwards. (C) describes an argument that proves an event happened and then mistakes that for proving what caused it. But the author's conclusion is the event itself, that the ice sheet melted, not a claim about what caused the melting. The real problem is that the author has not even shown the melting happened at all. (C) might be tempting because the last sentence does talk about causes, listing warming and volcanic activity, so it can look like the author is reasoning about causation. Those causes, though, are brought in only to show that melting was possible. The author never concludes anything about which cause did it, so there is no confusion between an event and its cause to point to.
d
A claim that ███ █ ████ ███████ ███████████ ██ █████ ████████ ██ ████████ ████ █ ████████ ██████████ █████ ██ ██████
The claim that the ice sheet must have temporarily melted does not have “general application.” It is a claim about a particular ice sheet and that it must have melted around 3 million years ago. This does not apply to other ice sheets or other time periods.
e
An inconsistency that, ██ ██████████ ███ ████ ████ ███ ████████ ██████████ ██ ███████ ██ ██████ ████ ███ ██████████ ██ █████████
This accurately describes the argument's flaw. The puzzling fact is that fossils previously found only in ocean-floor sediments turned up under the central Antarctic ice. That oddity could be resolved in more than one way, but the author settles on a single resolution, that the ice melted and the sea submerged the continent. Other explanations go unaddressed. Maybe the fossils were carried to the site, or maybe the ground there was once seabed for some reason besides melting ice.