Critical Reasoning

It is theoretically possible that bacteria developed on Mars early in its history and that some
were carried to Earth by a meteorite. However, strains of bacteria from different planets would
probably have substantial differences in protein structure that would persist over time, and no
two bacterial strains on Earth are different enough to have arisen on different planets. So,
even if bacteria did arrive on Earth from Mars, they must have died out. The argument is
most vulnerable to which of the following criticisms?
A. It fails to establish whether bacteria actually developed on Mars.
B. It fails to establish how likely it is that Martian bacteria were transported to Earth.
C. It fails to consider whether there were means other than meteorites by which Martian bacteria
could have been carried to Earth.
D. It fails to consider whether all bacteria now on Earth could have arisen from transported
Martian bacteria.
E. It fails to consider whether there could have been strains of bacteria that originated on Earth
and later died out.

[spoiler]Why not E?[/spoiler]

Sub conclusion: No two bacterial strains on Earth are different enough to have arisen on different planets

Conclusion: Even if bacteria did arrive on Earth from Mars, they must have died out.

D. It fails to consider whether all bacteria now on Earth could have arisen from transported
Martian bacteria. => Weaken the conclusion. If bacteria developed from the Mar's bacteria, bacteria on Earth today is the descendant of the ancestor bacteria, which belongs to Mar. So, Mar's bacteria was not died out, it evolved.

Conclusion: Bacteria from Mars must have died out.

Evidence: Earth's bacteria strains aren't diff. enough.

Assumption: The bacteria couldn't have evolved enough to appear totally diff. All of Earth's bacteria couldn't be from Mars.

Question Rephrase: What is a weakness of the argument?

Prediction: The assumption might not be true.

The answer is D since it it the closest match to our prediction. E is irrelevant since the question is only concerned with whether there could be bacteria from Mars on Earth.

ya, it is D

Reasoning - No two strains on earth are different
Conclusion: bacteria are not originated from The meteorite from Mars.

Hit conclusion+Respect the reasoning -- What is the whole bacteria on earth are developed from the bacteria imported through Meteorite only? Solves

VivianKerr wrote:Conclusion: Bacteria from Mars must have died out.

Evidence: Earth's bacteria strains aren't diff. enough.

Assumption: The bacteria couldn't have evolved enough to appear totally diff. All of Earth's bacteria couldn't be from Mars.

Question Rephrase: What is a weakness of the argument?

Prediction: The assumption might not be true.

The answer is D since it it the closest match to our prediction. E is irrelevant since the question is only concerned with whether there could be bacteria from Mars on Earth.

I agree D is more apt. But I feel E is definitely not irrelevant, rather a close second.

So, what if the Earth's bacteria died out, and only the martian bacteria is present on Earth currently. Then also we could have a single protein structure.
The only difference between D & E have is the word 'all'. So if not all the structures of bacteria, which originated on Earth died (referring to E) then there might be some still present and hence that does not weaken the argument. Because it might have happened that some Earth bacteria died out and all Martial bacteria died out and hence we have some Earth bacteria still left and therefore we found only a single protein structure.
Let me know if I've gone too far with my imagination here.

@Jumsumtak But remember the question asks about "most vulnerable." Keep the focus on the argument, itself. The argument would be MOST vulnerable if proof was found that bacteria from Mars did NOT die out (a reversal of the conclusion). Mars is not mentioned in E.