Self-study
Geologist: The dominant view that petroleum formed from the fossilized remains of plants and animals deep in the earth's crust has been challenged by scientists who hold that it formed, not from living material, but from deep carbon deposits dating from the formation of the earth. ███ █████ ██████ ██ ███████ ██ ███ ████████ ██ █████████ ██ ███████████ █████████ ██████████ ███ ████ ██ ███████ █████████ ██ █ ██████ █████████
Untangling the Argument
This stimulus packs three different viewpoints into a short space, so it's worth slowing down to untangle them.
The dominant view is that petroleum formed from the fossilized remains of plants and animals deep in the earth's crust. In short: petroleum comes from ancient life.
The challenging scientists disagree. They think petroleum formed not from living material but from deep carbon deposits dating from the formation of the earth. In other words, they believe petroleum's origin is geological, not biological.
The geologist (the author) sides against the challenging scientists. She concludes that
You can think of this argument through a phenomenon-hypothesis lens. The phenomenon is the presence of biomarkers in petroleum. The geologist's hypothesis is that these biomarkers are there because the petroleum itself formed from living things. And from this, she concludes that the competing theory (deep carbon deposits) must be wrong.
Anticipation
For the geologist's argument to work, the biomarkers in petroleum have to be evidence that the petroleum formed from living things. But is that the only possible explanation for why biomarkers are in the petroleum? What if the biomarkers got into the petroleum some other way, even if the petroleum actually formed from deep carbon deposits?
If an answer can provide an alternate explanation for how biomarkers ended up in petroleum, that would show that the geologist's premise (biomarkers are present) doesn't guarantee her conclusion (the deep-carbon-deposit theory is wrong).
Here's a subtle hint from the stimulus that points in this direction. Notice the definition of biomarkers: molecules indicating
23.
Which one of the following, ██ █████ ████ ███████ ███ ███████████ █████████
a
Fossils have been ██████████ ████ ███ ██████ ██ ███████████
If you're attracted to (A), you might be reading it as "fossils don't have biomarkers," which would undercut the idea that fossilized life could be the source of the biomarkers in petroleum. But that's not what (A) says. It just says there have been fossils without biomarkers. In other words, some fossils don't have biomarkers. But plenty of other fossils could still have biomarkers, and those fossils could be the source of the biomarkers we find in petroleum.
Illusory inconsistency
Illusory inconsistency
Answer is attractive because it seems to (but doesn't actually) contradict the premises or conclusion. In other words, it feints an attack on the premises or conclusion. If correlation is present, the answer choice is often merely an outlier datapoint, which is actually entirely consistent with the correlation.
b
Living organisms only ███████ ████ █████ ███ ███████ ██████████
If you're attracted to (B), you might be assuming that petroleum had to form around the time the earth was formed. If that were true, then the fact that living organisms came along much later would suggest the petroleum couldn't have come from life. But the stimulus never says petroleum formed at or near the time of the earth's formation. That's what the deep carbon deposits date to, not the petroleum itself.
Petroleum could have formed long after the earth's formation, well after living organisms emerged. Maybe organisms lived, died, became fossils, and then the petroleum formed from those remains. (B) doesn't create any timeline conflict with the geologist's reasoning.
Illusory inconsistency
Illusory inconsistency
Answer is attractive because it seems to (but doesn't actually) contradict the premises or conclusion. In other words, it feints an attack on the premises or conclusion. If correlation is present, the answer choice is often merely an outlier datapoint, which is actually entirely consistent with the correlation.
c
It would take ████ ████████ ██ █████ ███ █████████ ██ ██████ ██████████
Even if it takes many millions of years for organisms to become petroleum, that doesn't make it unlikely. The earth is billions of years old. There's been plenty of time for organisms to live, die, and slowly transform into petroleum over millions of years. If you're attracted to (C), you might be assuming that petroleum had to form quickly, but nothing in the stimulus requires that assumption.
Illusory inconsistency
Illusory inconsistency
Answer is attractive because it seems to (but doesn't actually) contradict the premises or conclusion. In other words, it feints an attack on the premises or conclusion. If correlation is present, the answer choice is often merely an outlier datapoint, which is actually entirely consistent with the correlation.
d
Certain strains of ████████ ██████ ████ ██████ ███ ███████ ██████
This provides an alternate explanation for how biomarkers could have ended up in petroleum. The geologist assumed the biomarkers in petroleum are there because the petroleum formed from living things. But (D) offers a different possibility: bacteria thrive deep inside the earth's crust, which is where the deep carbon deposits are located. If living bacteria are present in the same area where petroleum forms from deep carbon deposits, those bacteria might be the source of the biomarkers.
Remember, biomarkers indicate the past or present existence of a living organism. The geologist treated the biomarkers as evidence of petroleum's ancient biological origin. But (D) suggests the biomarkers might reflect the present existence of bacteria living alongside the petroleum, not the origin of the petroleum itself. Petroleum could have formed from deep carbon deposits and still contain biomarkers, because the bacteria living nearby might have contributed those markers.
(D) doesn't prove the geologist is wrong. It doesn't establish that petroleum definitely came from deep carbon deposits. But it doesn't have to. It just needs to show that the geologist's evidence (biomarkers in petroleum) doesn't guarantee her conclusion (the deep-carbon-deposit theory is wrong). By providing a plausible alternate source for the biomarkers, (D) weakens the argument.
Alternate explanation
Alternate explanation
Weaken: Introduce or support an alternate explanation for a phenomenon.
Strengthen: Helps to eliminate an alternate explanation for a phenomenon.
e
Some carbon deposits ████ ██████ ████ ███ ██████████ ███████ ██ ███████
Pay close attention to which carbon deposits the scientists are talking about. The scientists' theory involves
Even if some carbon deposits out there were formed from plants, those aren't the deposits at issue in this argument. The geologist is responding to a theory about carbon deposits that predate life entirely. (E) has no impact on that debate.
Directionally wrong
Directionally wrong
Answers that, if they have any effect, do the opposite of what we want (weaken when we're trying to strengthen, or strengthen when we're trying to weaken).