Volcanic-Eruption Theory

Answer choices

1. A

   Opposite (if anything)4% picked this

   Fragments of meteorites that have struck the Earth are examined and found to have only minuscule amounts of iridium

   If this answer helped us to argue that a meteorite impact is what killed the dinos, we'd consider it. But this answer does nothing like that. Meteorites have iridium in mostly solid form. Volcanos erupt iridium in a gaseous form (iridium hexafluoride). The gas form is more likely to explain the worldwide later of iridium we see from that era than is the solid form, so being told that meteorites don't have much of the gas form makes meteorites seem less likely to be the cause of the global iridium layer that coincides with the dinos' demise.

   4%
2. B

   Correct65% picked this

   Most diapir eruptions in the geological history of the Earth have been similar in size to the one that occurred in India at the

   Why this is right

   This hurts the plausibility of the volcano theory, which held that "diapir eruptions led to releases of CO2 which led to poisonous climate change for the dinos". This is doing a classic Cause w/o Effect style weakener, providing us with tons of data points in which diapir eruptions happened (the supposed Cause), but they didn't cause a period of climate change (the supposed Effect).

   Skill tested: Weaken · how this choice captures the passage's function is the move to repeat next time.

   65%
3. C

   No Impact4% picked this

   There have been several periods in the geological history of the Earth, before and after the Cretaceous period, during which large numbers

   This just tells us that other extinctions have happened, but it isn't giving us any clue about what caused these extinctions (and thus isn't helping us assess what caused the extinctions of the dinos and lots of marine species 66 million years ago).

   4%
4. D

   Too Weak7% picked this

   The frequency with which meteorites struck the Earth was higher at the end of the Cretaceous period than at

   This is telling us that closer to the end of the Cretaceous period (which is when the dinosaur extinctions occurred, 66 million years ago), there was an uptick in Earth getting hit by meteorites. That would start to seem like support for the Alternate Explanation that the dino extinctions were caused by a large meteorite, not by volcanic eruptions. But the Earth is always getting hit by meteorites (we have yearly meteor showers that are harmless displays of "shooting stars"). The meteorite theory is specifically about one huge mamma-jamma that hit the earth. It doesn't really matter whether that gigantic meteorite happens during a period of higher or lower meteorite impacts in general. In other words, saying that the Earth was getting hit by more meteorites than in a previous era isn't suggestive enough that ONE of those meteorites was a huge one that killed the dinos.

   7%
5. E

   No Impact19% picked this

   Marine species tend to be much more vulnerable to extinction when exposed to a dramatic and relatively sudden change in sea level than when

   This answer makes it seem surprising that there were lots of marine extinctions that coincided with the dinos' demise, since the sea level had changed pretty gradually. But we already know there WERE marine extinctions. We're trying to assess whether they were caused by a meteorite impact, bad eruptions, or something else.

   19%