Sedimentary rock hardens within the earth’s crust as layers of matter accumulate and the pressure of the layers above converts the layers below into rock. ███ ██████████ █████ ██ ███████████ ████ ████ ████████ ██ ███████ ██████ ██ ███ ███████ ███████ ███ ████ █████████ ██ ███████ ███ █ ██████ ████ █ █████████ ████████ ████ ███ █████ ████ █████ ███████ █████ ████ ██████████ ███ ████ ██ ███████ ████████ ██ ███ █████████ ██████ ███ ██████████ ████████ ████ █ █████████████ █████████ ████ ███ █████ ██████ █ ████ █████ ██ █████████████ █████ ███ █████ ████ ████ ██████████ ███████ ██ █████ █████ ██ ████████ ████ █████ ███████ ███ ██ ███ ██████ ███████████ █████ ███ ██ ██████ █ █████ ██ ████████████ █████
Here we have a phenomenon-hypothesis argument, concluding with the hypothesis that a meteorite hit earth about 60 million years ago. The key evidence supporting this hypothesis is a layer of iridium-rich sedimentary rock. This is useful evidence because meteorites contain more iridium than does the earth's crust, and a collision could have released a huge amount of iridium dust that later settled into a new layer of rock.
That's a lot of information, but we can still fall back on the same weakening strategies as with any phenomenon-hypothesis argument. We can find an alternative explanation to account for the iridium layer, without needing to involve meteorites at all. We could also find evidence to rule out a meteorite collision directly.
Which one of the following, ██ █████ █████ ███████ ███ █████ ████ ███ ████████████ █████ █████████ ██ ███ ███████ ██ ████████ ███ ███ █████████ █████████ ███████
The huge dust █████ █████████ ██ ███ ███████ █████ ████ ███████ ███ ████████████ ██ ████████ ███ ███████ ███ █████████ ████████████
This is just a secondary effect of the hypothesized collision. Since we don't know whether this secondary effect actually happened or not, it doesn't help us to weaken the hypothesis.
A layer of ███████████ ████ █████ ████████ ██ █████ ██ ███████
This isn't an issue for the argument, since the hypothesized collision would have occurred 60 million years ago. That's plenty of time for a dust cloud to settle and harden.
Layers of sedimentary ████ ███ ████ ██ █████████ ███ █████ ██ ███████████ ██████ ███████ ██ ███ ████ ███████ ████████
(C) is ultimately unrelated to the argument, which aims to explain why this layer of rock is so rich in iridium. The uses of sedimentary rock to determine dates isn't relevant to how the iridium got to this particular layer in the first place.
Sixty million years ███ █████ ███ █ █████ ██ ████████ ████████ ██ █████ ███ ██████ ██████ ████ ███ █████████ ██████ ████ ████████████ ████ ███████
Here we have our alternative explanation for why this layer of rock has so much iridium. (D) accounts for the phenomenon without any need for meteorites, which then leaves the argument's conclusion without support.
The iridium deposit ████████ ██ █████ ███ ████ ████ ████ ████ ██████ ███████ ██████ ███████ ███ ████ ██████████ ████ █████████ ████ ████ ████████ ███████████ ████ ██████ ██ █ █████████ ██████████
If anything, (E) strengthens the argument by providing corroborating evidence that there was a meteorite collision around 60 million years ago. It certainly doesn't undermine such a collision having happened.
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