Showing the same for me

I really focused on the "should have" part of this question.

At first I chose A because I thought the "should have" implied that there was A theory (not necessarily a theory in the passage) that hypothesized LHB struck Earth. While this theory wasn't mentioned or talked about in detail in the rest of the passage, I thought the author was phrasing it with a degree of uncertainty to explain that the theory existed or that at least you couldn't say with certainty that it DID affect Earth. I realized that "support" was a little too far for this answer, and I changed my tune on BR.

On BR, I chose B because, again, the "should have" part of the sentence made me think that the author was trying to imply something about the lack of evidence to make a conclusive statement regarding LHB's effect on Earth. It seemed to me the author would not have chosen to use this language unless they did not have the evidence necessary to make a conclusive statement. It did not seem necessary to me that the author continue this line of questioning in the passage for the purpose of this sentence to be questioning. The explanation indicates that it's wrong for this reason - that the author does not imply or explain any lack of Earth-based evidence anywhere else. I understand that, but I don't completely agree that the sentence cannot be taken to mean that there is a question/some uncertainty about the LHB evidence on Earth. I understand that the purpose of the passage as a whole is not to investigate this line of questioning, but why does that mean this sentence does not explore that idea?