Self-study
Although the geological record contains some hints of major meteor impacts preceding mass extinctions, Support there were many extinctions that did not follow any known major meteor impacts. █████████ █████ ███ ████ ███████ ██ █████ ██████ ███████ ████ ██ ███ ████ ██ ████ ████ ████████ ██ ████ ████████████ ████ ███ ██████████ ██████ ████████ ████ █████ ██ ██ ██████████ ██████ ████ ███████ █████ ██████ ███████ ███ ████ ████████████
Summary
The author concludes that there is no consistent causal link between major meteor impacts and mass extinctions. This is the based on the following:
Many extinctions didn’t follow major meteor impacts.
Many major meteor impacts were not followed by mass extinctions.
Missing Connection
The premises don’t establish what implies that there’s “no consistent causal link” between major meteor impacts and mass extinctions. Although we know that many extinctions didn’t follow such impacts, and that many impacts weren’t followed by such extinctions, how do we know that this isn’t a consistent causal link?
We want to establish that if many extinctions didn’t follow major meteor impacts or if many major meteor impacts were not followed by mass extinctions, then this proves there’s no consistent causal link between such impacts and such extinctions.
21.
Which one of the following ███████████ ███████ ███ ██████████ ██████████ ██ ██ ████████ █████████
a
If there were █ ██████████ ██████ ████ ███████ █████ ██████ ███████ ███ ████ ████████████ ████ ███ █████ ██████ ███████ █████ ██ ████████ ██ ████ ████████████
(A) establishes that in order for there to be a consistent causal link between the impacts and mass extinctions, then ALL major meteor impacts would be followed by such extinctions. We know from one of our premises that many major meteor impacts were NOT followed by such extinctions. This triggers the contrapositive of (A), which would establish that there is NO consistent causal link.
b
Major meteor impacts ███ ████ ███████████ ██████ ██ ████████████ ████████ ██████ ██████ ████ ████ ███████████ ████ ████████ █████ ██████ ████████
(B) establishes that in order for there to be a consistent causal link, it’s required that many mass extinctions have followed major meteor impacts. But we don’t know that this requirement hasn’t been met. Although we do know that many mass extinctions have not followed major meteor impacts, it’s still possible that many such extinctions have followed such impacts, too.
c
Of the mass ███████████ ████ ███ ███ ██████ ███ █████ █████ ██████ ████████ ███ ██ ███ ████████ █████ ██████ ███████ ██ █████ ███ ██████████ ██████ ████████ ██ ██████
(C) doesn’t establish what is required for a “consistent causal link” between extinctions and meteor impacts, so it can’t make the argument valid.
d
If there is ██ ██████████ ██████ ████ ███████ █████ ██████ ███████ ███ ████ ████████████ ████ ███ ███ ████ ███████████ █████ ████ ████████ █████ ██████ ████████
(D) establishes what would be true IF there is no consistent causal link. But we’re trying to reach the conclusion that there is no consistent causal link. We don’t want “no consistent causal link” to appear in the “IF” part of an “If, then” answer. We want it to appear in the “then” part.
e
There could be █ ██████████ ██████ ████ ███████ █████ ██████ ███████ ███ ████ ███████████ ████ ██ ███ █████ █████ ██████ ██████ ███ ████ ████████ ██ █ ████ ███████████
(E) tells us about one circumstance under which there can be a consistent causal link. But we’re trying to prove that there’s NO consistent causal link.