rulez161 wrote:
Although the geological record contains some hints of major meteor impacts preceding mass extinctions, there were many extinctions that did not follow any known major meteor impacts. Likewise, there are many records of major meteor impacts that do not seem to have been followed by mass extinctions. Thus the geological record suggests that there is no consistent causal link between major meteor impacts and mass extinctions.
Which one of the following assumptions enables the argument’s conclusion to be properly inferred?
(A) If there were a consistent causal link between major meteor impacts and mass extinctions, then all major meteor impacts would be followed by mass extinctions.
(B) Major meteor impacts and mass extinctions cannot be consistently causally linked unless many mass extinctions have followed major meteor impacts.
(C) Of the mass extinctions that did not follow any known major meteor impacts, few if any followed major meteor impacts of which the geological record contains no hints.
(D) If there is no consistent causal link between major meteor impacts and mass extinctions, then not all mass extinctions could have followed major meteor impacts.
(E) There could be a consistent causal link between major meteor impacts and mass extinctions even if not every major meteor impact has been followed by a mass extinction.
Argument:
There are some hints of mass extinctions after meteor impacts.
There were many extinctions that did not follow any known major meteor impacts.
There are many records of major meteor impacts that do not seem to have been followed by mass extinctions.
(Basically, the argument is saying that though some mass extinctions happened after major meteor impacts, many mass extinctions did not happen after known meteor impacts. Also, many meteor impacts were not followed by mass extinctions. )
Conclusion: So, record suggests that there is no consistent causal link between major meteor impacts and mass extinctions.
We want the conclusion to be properly drawn. So if we take the correct option to be true, it MUST lead to the conclusion to be true.
Let's see what happens when we take each option to be true.
(A) If there were a consistent causal link between major meteor impacts and mass extinctions, then all major meteor impacts would be followed by mass extinctions.
If condition - If A (consistent causal link between major meteor impacts and mass extinctions) then B (all major meteor impacts would be followed by mass extinctions)
A implies B
Not B implies not A.
It is given to us that all major meteor impacts were not followed by mass extinctions. There were many major meteor impacts that were not followed by mass extinctions. So it is given to us that B is not true. So 'Not B' is given to us.
Not B implies Not A.
So we CAN CONCLUDE that there is no consistent causal link between major meteor impacts and mass extinctions. This is the conclusion of our argument. We can conclude the conclusion if we take this option to be true.
Hence (A) is the answer.
(B) Major meteor impacts and mass extinctions cannot be consistently causally linked unless many mass extinctions have followed major meteor impacts.
This tells us that "Many mass extinctions have followed major meteor impacts" is necessary for "consistently causally linking major meteor impacts and mass extinctions". We do know that some mass extinctions have followed major meteor impacts. Have many mass extinctions followed major meteor impacts, we don't know.
(C) Of the mass extinctions that did not follow any known major meteor impacts, few if any followed major meteor impacts of which the geological record contains no hints.
Doesn't help us conclude that there is no consistent causal link. We don't know when can we establish whether there is a consistent causal link or not. Option (A) defines when there is a consistent causal link.
(D) If there is no consistent causal link between major meteor impacts and mass extinctions, then not all mass extinctions could have followed major meteor impacts.
If condition - If A (NO consistent causal link between major meteor impacts and mass extinctions) then B (not all mass extinctions could have followed major meteor impacts)
A implies B
Not B implies not A.
We need to establish A (NO consistent causal link between major meteor impacts and mass extinctions). With an if condition, nothing establishes A. We can establish B or 'not A'.
Hence, this option is incorrect.
(E) There could be a consistent causal link between major meteor impacts and mass extinctions even if not every major meteor impact has been followed by a mass extinction.
This is premise against our conclusion.
Answer (A)