There are just two ways a moon could have been formed from the planet around which it travels: either part of the pla...

shunhe on September 13, 2020

Hi @lsatstudier1,

Thanks for the question! So let’s take a look at the stimulus first. We’re told that there’s only two ways a moon could’ve been formed from the planet around which it travels: (1) planet’s outer shell spun off, or (2) large object like comet or meteoroid hits the planet really hard. We’re also told that earth’s moon consists primarily of materials different from those of Earth’s outer shell.

Now we need to look for an answer choice that justifies the following conclusion: Earth’s moon wasn’t formed from a piece of the earth. So we want something that suggests that the moon wasn’t formed from the earth, so something that makes both of these possibilities less likely. We’re not looking for something that supports the second condition, since that would still mean the Earth’s moon was formed from a piece of the earth, just the inside piece. Now take a look at (B), which tells us that earth’s moon consists primarily of elements that differ from those inside Earth. Well, if that’s true, then we know it’s probably not (2). And we already know that it’s probably not (1) because of the last sentence in the stimulus. So adding this sentence in makes us think that the moon probably wasn’t formed from the earth, and that’s the conclusion we want to justify! So (B) is the correct answer.

Hope this helps! Feel free to ask any other questions that you might have.

lsatstudier1 on September 15, 2020

Thanks for clarifying!! I realize I read the question stem wrong...