Self-paced
Support There are just two ways a moon could have been formed from the planet around which it travels: either part of the planet’s outer shell spun off into orbit around the planet or else a large object, such as a comet or meteoroid, struck the planet so violently that it dislodged a mass of material from inside the planet. █████████ ████ ████████ █████████ ██ █████████ █████████ ████ █████ ██ ███ █████████ █████ ██████
Objective: Justify a Conclusion
Although the stimulus just gives us facts rather than a full argument, we're still asked to justify a certain conclusion. That conclusion, found in the question stem, is that Earth's moon was not formed from a piece of the Earth.
The existing support we have from the stimulus tells us that there are only two ways that the Moon could have been formed from a piece of the Earth. First, it could be a detached piece of the outer shell—but the Moon is made of different materials than Earth's outer shell. Second, it could result from a violent meteoroid strike that dislodged materials from inside the Earth.
Essentially, the stimulus presents two exhaustive possibilities, and eliminates one. If we want to more fully justify the conclusion that the Moon was not formed from a piece of the Earth, our best approach is to eliminate the remaining possibility of a meteoroid strike dislodging materials from inside the Earth. That's what the correct answer will do.
13.
If the statements above are █████ █████ ███ ██ ███ ██████████ ██ ████ █████ █████ ████ ████ ██ ███████ ███████ ███ ██████████ ████ █████████ ████ ███ ███ ██████ ████ █ █████ ██ ███ ██████
a
The moons of ████ ███████ ██ █████████ █████ ██████ ████ ███ ██████ █████████ ████ ███ ██████████ █████ ███████
We already know Earth's moon wasn't formed from Earth's outer shell, because it's made of different materials. (A) doesn't help us eliminate the remaining possibility that the Moon was formed from materials inside the Earth.
b
Earth’s moon consists █████████ ██ ████████ ████ ██████ ████ █████ ██████ ███ ██████
In other words, the Moon likely was not formed from materials inside the Earth that were dislodged by a meteoroid strike. If that had been the case, we would expect the material composition to match. (B) lets us eliminate the remaining possibility for how the Moon could have been formed from a piece of the Earth.
c
Earth’s gravity cannot ████ ███████ █ █████████ ███ ██████ ██ ████ ███ █████ ██ ███ █████
(C) does the opposite of what we want: it eliminates a possible mechanism for the Moon not having been formed from a piece of the Earth. This only makes it less likely that our desired conclusion is true.
d
The craters on ███ ███████ ██ █████████ ████ ████ ████ ██ ███ ████ ██████ ██ ████ █████████ ██ █████ ███████████
The only meteoroid strikes we're interested in are strikes on the Earth that could have dislodged material to become the Moon. And even then, we want to show that such a thing didn't happen. Meteorites striking the Moon doesn't help with that.
e
Comets and large ██████████ ████████ ████ ██ ████ ████ ███████
We already know it's possible for comets and meteoroids to hit planets so hard that they create new moons. Moving at high speeds is consistent with this, but regardless, we want to eliminate the possibility of a meteoroid strike creating the Moon.