#23 - Geologist: The dominant view that petroleum formed

[Administrator]

Complete Question Explanation

Weaken. The correct answer choice is (D).

A geologist tells us that while some people have challenged the dominant view of how petroleum formed, claiming that it came not from living material but from very old deep carbon deposits, those people have to be wrong because petroleum has biomarkers in it, which are the remains of living things. We are then tasked with weakening this claim, which means we have to attack the geologist who is attacking the other people, a potentially mind-bending double negative. To weaken her attack, we want to either 1) strengthen the opposition (by providing evidence that deep carbon, rather than living material, is the source of petroleum), or undermine her evidence (by showing that the presence of biomarkers may not mean what she thinks it means). With that in mind, we can move to the answers - no more specific prephrase should be required.

Answer choice (A): The first answer choice neither supports the deep carbon theory nor challenges the geologist's reliance on those biomarkers, and is therefore a loser. The absence of biomarkers in some fossils tells us nothing about what their presence in petroleum does or does not prove.

Answer choice (B): The fact that living organisms came much later than when those deep carbon deposits formed still tells us nothing about where petroluem did or did not originate, since we don't know how old petroleum is or how long it would have taken to form from either source. This also does nothing to undermine the importance of the biomarkers found in petroleum.

Answer choice (C): Much like answer B, the time it takes for petroleum to form does not, by itself, support the deep carbon theory or weaken the argument based on the presence of biomarkers. Perhaps petroleum formed from living material that is many millions of years old?

Answer choice (D): This is the correct answer choice. This answer matches the second part of our prephrase by weakening the value of biomarkers in petroleum as evidence. If bacteria (which are living things, even if they are not plants or animals) are found deep in the earth's crust, down where the deep carbon is, it's possible that petroleum formed from deep carbon and just happened to have captured some living material in it in the process. Their presence in the petroleum tells us nothing about how the petroleum itself formed. This answer is the equivalent of saying that a fly in your soup does not prove that it is not vegetable soup.

Answer choice (E): Don't be distracted by this answer, which deals with the wrong carbon deposits. The author is saying that petroleum could not have formed from deep carbon deposits dating to the earth's formation, because there are biomarkers in petroleum. Any carbon deposits that formed from decaying living material must have been formed long after the formation of the earth, and in any event this answer tells us nothing about whether the "some" deposits mentioned have anything to do with the formation of petroleum.

This argument does have a strong causal element to it, discussed in Dave Killoran's post from November 2018 in this thread, which is worth reading next if this explanation proves insufficient to satisfy your needs.

[Brandonhsi]

Hello,

I selected (A) as my answer choice. I can understand why (D) weakens the argument. However, I believe (A) also weakens the argument a bit.

Since it is possible fossils doesn't have biomarkers (from (A)), it is possible the petroleum is not from living material (therefore, could be from others, like deep carbon deposits). Therefore, (A) weakens the argument a bit.

Am I interpret this question wrong in this way? Thanks!

Brandon

[Emily Haney-Caron]

Hi Brandon,

A does not weaken the argument because it only tells us about fossils, not about petroleum - even if fossils exist without biomarkers, that doesn't help explain why petroleum DOES have biomarkers.

Does that help?

[emilysnoddon]

I had a lot of difficulty with this problem. I am having a hard time seeing why D weakens the argument. I don't understand what certain trains of bacteria has to do with petroleum. Can someone please clarify this for me? Thank you!!

[Clay Cooper]

Hi emily,

Thanks for your question.

There are some who argue that petroleum could have formed, not from plants and animals, but from carbon deposits left over from the earth's formation; our geologist claims that these people are wrong, because there are biomarkers in petroleum, and biomarkers indicate the presence of life; our geologist clearly thinks that these biomarkers are left over from the plants and animals that decayed to form the petroleum.

However, if D were true, the bacteria within the earth's crust could have provided the biomarkers, and it might still be possible that petroleum does not come from plants and animals, but instead from carbon deposits left over from the earth's formation. (Note that bacteria are neither plants nor animals.)

The bacteria, in other words, would provide a plausible alternate cause for biomarkers' having come to be in the petroleum, and would thus weaken its evidentiary value. Since the presence of these biomarkers is the only evidence the geologist offers us, doing so would significantly weaken his conclusion.

[emilysnoddon]

Thank you, that explanation helps a lot. I just want to make sure my train of thought follows similarly... my prephrase for the question was to find an answer that showed that petroleum came from deep carbon and not living organisms, instead my prephrase should have been to show that petroleum didnt come from plants and animals. I eliminated D because I felt as though since bacteria is a living organism, it would strengthen the geologists argument. So basically I misunderstood the argument to be broader (encompassing all living things) than it really was. Is this correct?

Thanks!

[Clay Cooper]

Hi emily,

Yes, that is basically correct. Bacteria is living but is not a plant or animal, so you were thinking of it too broadly if you included bacteria in that category. But don't feel bad, I did the same thing at first (hence my note in the previous post).

Also, don't stress too much about your prephrase. If anything, I would try to be less specific with it - it's possible that evidence will be introduced that bolsters the carbon deposit theory without affecting the living thing theory, or its possible that what will happen here happens, and the living thing theory will be weakened. I think it is unreasonable to expect yourself to be able to prephrase as specifically as it sounds like you do.

[bk1111]

Hi, I had a very hard time with this question as well - all of the answer choices seemed out irrelevant to me. At the end, I went with B, as I thought it boosted the argument of the scientists who challenged fossilized plants/animals theory.

For this question, am I simply weakening the geologists' argument in favor of the deep carbon deposits theory? I think that is what led me to choose B.

[AthenaDalton]

Hi bk111,

Yes, the prompt asks us to weaken the geologist's argument (who believes that petroleum formed from living organisms), so focus on the choices that undercut the geologist's theory.

[dbpk]

When the geologist says "their theory is refuted", he refers to the scientists who argue that petroleum was formed "NOT from LIVING material" but from carbon deposits.
Although the dominant view refers specifically to plants and animals, the scientists to whom the geologist's argument is directed claim that petroleum does not form from living material generally. This is why I ruled out D because bacteria would count as living material, which would fail to weaken the geologist's argument.

Am I misreading the stimulus? Any help appreciated!