Q14 - The axis of Earth's daily

[orangecellny]

i am having trouble understanding how to approach this problem. i am unable to understand the proper diagramming that needs to be done in order to determine the correct answer.

i would greatly appreciate any help


thanks in advance

[timmydoeslsat]

i am having trouble understanding how to approach this problem. i am unable to understand the proper diagramming that needs to be done in order to determine the correct answer.

i would greatly appreciate any help


thanks in advance

This is definitely a stimulus that would be beneficial to diagram, as is often the case with must be true questions.

So the first sentence tells us that the Earth's axis is tilted at an angle of roughly 23 degrees.

So far this is just a fact that we know.

Next sentence says that the angle can be kept stable only by the grav. influence of Earth's moon.

This is a conditional relationship. Can be kept stable only by X.

Stable ---> X

Or in this case:

Stable tilt ---> Grav. influence of Earth's moon

So far we have a fact and a conditional statement that are not interacting with each other.

Next sentence states that without a stable and moderate tilt, a planet's climate is too extreme and unstable to support life.

We can diagram this statement like this:

~Stable tilt ---> ~Planet support life

So we do see now that these statements can be linked up and we can make inferences or conclusions about them.


Stable tilt ---> Grav. influence of Earth's moon
~Stable tilt ---> ~Planet support life


There are two nice things about these conditional statements.

1) We can combine them.
2) We know what happens when stable tilt and we know what happens when ~stable tilt.

Those are the only two possibilities in existence, and we have information about either occurrence.

I can see that to combine these two statements, I need to take the contrapositive of the second statement to align the statements in logical order to where we get this:

Stable tilt ---> Grav. influence of Earth's moon

Planet support life ---> Stable tilt

........

Planet support life ---> Stable tilt ---> Grav. influence of Earth's moon


Answer choice B must be true. It is a statement using the contrapositive of our long logic chain.

[ohthatpatrick]

Sweet reply!

Let me just add onto that wonderful explanation the other way that chain could look.

Timmy gave us:

Planet Support Life --> Stable Tilt --> Grav Infl of Moon

And the contrapositive of that chain would look like (B):

~Grav Infl of Moon --> ~Stable Tilt --> ~Planet Support Life

====other answers
(A) as discussed, the only conditional we have about Supporting Life is Planet Support Life --> Stable Tilt
whereas this answer is saying,
Sufficient Moon --> Planet Support Life
You know this answer is unjustified if you realize that Support Life was given to us as a Suff condition (left side idea), and this answer is acting like we can use Support Life as a Nec condition (right side idea)

(C) Same problem as A. (C) is saying
Stable Tilt --> Support Life

(D) We can't prove that nothing else effects the magnitude of the tilt. Remember, we know the Moon is integral to maintaining the stability of the angle. Nothing here says the Moon itself is responsible for the magnitude of the angle.

(E) this translates as
More than one Moon --> ~Support Life
The conditional we were given that relates to ~Support Life was
~Stable Tilt --> ~Support Life

Is there any way to prove that
More than one Moon --> ~Stable Tilt ??

No there is not. Just because the Earth's stable tilt requires its one, nearby Moon, that doesn't mean we can assume that all stable tilts require one moon.

This answer is also trying to tempt people who want to use the information about Mars to draw a more general, universal conclusion. (no pun intended)

[drothhello]

Timmy and Patrick Friends, I do appreciate your analysis but here is my question:

Answer B says that if earth's moon were to leave its oribit.

Whoa whoa whoa, I ain't no astronomer guy with a stethoscope or anything , so why does the moon have to be in earth's orbit?

Why can't the moon leave earth's orbit but still have a gravitational influence? Isn't that like a science assumption? For this question you have be like a damn carl saga genesis or something.

[TimothyS21]

I'm just confused on why answer choice D is wrong. In the stimulus it says that the gravitational influence of the only the Moon is the only reason why the tilt is stable. Am I missing something?