Two different dates have been offered as the approximate end point of the last ice age in North America. The first date was established by testing insect fragments found in samples of sediments to determine when warmth-adapted open-ground beetles replaced cold-adapted arctic beetles. The second date was established by testing pollen grains in those same samples to determine when ice masses yielded to spruce forests. The first date is more than 500 years earlier than the second.

Summary
Two dates have been proposed as the approximate end point of the last ice age in North America:
First Date: Based on the presence of warmth-adapted open-ground beetles replacing cold-adapted arctic beetles in sediment samples.
Second Date: Based on the emergence of spruce forests as indicated by pollen grains found in the same sediment samples.
The first date (beetles) is over 500 years earlier than the second date (spruce forests).

Strongly Supported Conclusions
Warm adapted beetles appeared before the emergence of spruce forests.

A
Toward the end of the ice age, warmth-adapted open-ground beetles ceased to inhabit areas where the predominant tree cover consisted of spruce forests.
There is no information about what happened to warm-adapted beetles after the emergence of spruce forests. The forests emerged *after* the beetles
B
Among those sediments deposited toward the end of the ice age, those found to contain cold-adapted arctic beetle fragments can also be expected to contain spruce-pollen grains.
This is anti supported. The cold beetles came before the warm beetles, which in turn came before the spruce pollen grains. There is no support for them being together.
C
Ice masses continued to advance through North America for several hundred years after the end of the ice age.
The stimulus says nothing about whether ice masses advanced or not.
D
The species of cold-adapted arctic beetle that inhabited areas covered by ice masses died out toward the end of the last ice age.
The stimulus does not give information as to when the ice age *actually* ended (there are just two proposed dates). Thus, it is unreasonable to assume that the cold beetles died towards the end.
E
Toward the end of the ice age, warmth-adapted open-ground beetles colonized the new terrain opened to them faster than soil changes and seed dispersion established new spruce forests.
The stimulus says that the warm-adapted beetles replaced cold-adapted beetles 500 years before the emergence of spruce forests. Thus, it is supported that the beetles colonized the terrain faster than the establishment of the forests.

43 comments

Essayist: Common sense, which is always progressing, is nothing but a collection of theories that have been tested over time and found useful. When alternative theories that prove even more useful are developed, they gradually take the place of theories already embodied in common sense. This causes common sense to progress, but, because it absorbs new theories slowly, it always contains some obsolete theories.

Summary

Common sense is always progressing.

Common sense is a collection of theories that have been tensed and found useful over time.

Alternative theories that are even more useful gradually replace the theories that are common sense.

This replacement happens slowly, so common sense always contains some obsolete theories.

Notable Valid Inferences

In common sense, there are always at least some theories that have more useful alternatives.

A
At least some new theories that have not yet been found to be more useful than any theory currently part of common sense will never be absorbed into the body of common sense.

This could be false. The stimulus discusses theories that are already developed and proven to be more useful. Further, the stimulus doesn’t discuss which theories will never be absorbed into common sense.

B
Of the useful theories within the body of common sense, the older ones are generally less useful than the newer ones.

This could be false. The stimulus does not give any relationship between age of theory and usefulness.

C
The frequency with which new theories are generated prevents their rapid absorption into the body of common sense.

This could be false. The stimulus just says that common sense absorbs new theories slowly; we don’t know the reason for this slow progress.

D
Each theory within the body of common sense is eventually replaced with a new theory that is more useful.

This could be false. We know that some theories are eventually replaced; we don’t know that each theory will be replaced.

E
At least some theories that have been tested over time and found useful are less useful than some other theories that have not been fully absorbed into the body of common sense.

This must be true. Progress is slow, so it takes time for alternative theories that have been proven to be more useful to be absorbed into common sense. Until these alternatives are absorbed into common sense, the theories in common sense are less useful than the alternatives.


17 comments

Editorialist: Some people argue that we have an obligation not to cut down trees. However, there can be no obligation to an entity unless that entity has a corresponding right. So if we have an obligation toward trees, then trees have rights. But trees are not the sort of things that can have rights. Therefore, we have no obligation not to cut down trees.

Summary
The author concludes that we don’t have an obligation not to cut down trees. Why?
Because if an entity doesn’t have a corresponding right not to be cut down, then there is no obligation to that entity. And we know trees aren’t the kind of thing have have rights.

Notable Assumptions
We know from the premises that trees don’t have rights; so we don’t have any obligation toward trees not to cut them down. But does that prove we have no obligation at all not to cut down trees?

The flaw in the argument is that we might have an obligation to entities besides trees not to cut trees down. For example, maybe we’re obligated to our future children not to cut down trees.

The author must assume that we do not owe an obligation to other entities not to cut down trees.

A
If an entity has a right to certain treatment, we have an obligation to treat it that way.
Not necessary, because we already know that trees don’t have rights. So whatever must be true about things that do have rights doesn’t relate to the author’s reasoning.
B
Any entity that has rights also has obligations.
Not necessary, because we already know that trees don’t have rights. So whatever must be true about things that do have rights doesn’t relate to the author’s reasoning.
C
Only conscious entities are the sort of things that can have rights.
The concept of “conscious entities” has nothing to do with the reasoning of the argument. So (C) isn’t necessary.
D
Avoiding cutting down trees is not an obligation owed to some entity other than trees.
Necessary, because if it were not true — if avoiding cutting down trees IS an obligation owed to some entity other than trees — then we actually may still be obligated not to cut down trees, even if that obligation isn’t owed to the tree itself.
E
One does not always have the right to cut down the trees on one’s own property.
The argument concerns whether we have an obligation not to cut down trees. Whether we have a right to cut down trees is a separate issue.

29 comments