PT92.S1.Q23 - Isotopes and life on Mars

kat12345-1

Does anyone have any tricks for getting this one correct with zero understanding of science? I skipped it and honestly would happily skip it again on the actual LSAT. I'm probably distracted by the science jargon but didn't want to waste time parsing it out. Is there a cookie cutter format under the jargon that I missed?

maxjab00

It's not terrible, you don't really need to understand what these term means. All you really need to know about isotopes is that a ratio between them is important. When you see the isotope names, think of them as a ratio.

In short, the argument says:

P1. Biological activity -> Change in the ratio of isotopes
P2. Martian asteroid does not have ratio of isotopes that indicate life
C. No life on Mars.

In other words, it is saying:

P1. A -> B (on Earth)
P2. B (on Martian meteorite)
C. A (on the planet Mars)

This is weaken/except, so there are four weakening AC and one that doesn't.

A. is saying that maybe life that is not from Earth creates a different ratio. That means premise 1 could be more like A -> C on Mars, so it weakens the argument.

B. is saying that climate on Earth plays a large part in the ratio, and so a different climate might have a different ratio. Same as AC A, it alters premise 1 and weakens the argument.

D. is saying that just because there is general rule that life creates that certain ratio, it does not mean that all parts of the planet will have that ratio. If there is life, the ratio will be there. However, a rock 1000 ft. below the surface might not. That is because there is no life in that rock, but there is still life elsewhere on Earth. So, maybe the Martian sample is similar to that rock 1000 ft. below the ground. That particular rock has no life, but it does not mean that Mars as a whole has no life.

E. is saying that the isotope ratio on Mars is not always the same. So, perhaps the ratio was the same as the one found on Earth in the past. This challenges premise 2 by saying that maybe there was B on Mars.

C. is the correct answer. It says that that isotope ratio on the meteorite is the same as it is on Mars. One possible objection to the argument was that maybe the meteorite is not a good representation of Mars (similar to how AC D says suggests that the ratio found on Earth may not be perfectly representative), but this AC says that it is. So, this does not weaken, but can actually strengthen the argument.