PrepTest 92+, Section 1, Question 23
On Earth, biological activity leads to a change in the ratio of isotope S-34 to isotope S-32. However, a newly discovered meteorite of Martian origin exhibits ratios of these elements found only in terrestrial minerals dating from before the beginning of life on Earth. Therefore, it is unlikely that life occurred on Mars.
On Earth, biological activity leads to a change in the ratio of isotope S-34 to isotope S-32. However, a newly discovered meteorite of Martian origin exhibits ratios of these elements found only in terrestrial minerals dating from before the beginning of life on Earth. Therefore, it is unlikely that life occurred on Mars.
On Earth, biological activity leads to a change in the ratio of isotope S-34 to isotope S-32. However, a newly discovered meteorite of Martian origin exhibits ratios of these elements found only in terrestrial minerals dating from before the beginning of life on Earth. Therefore, it is unlikely that life occurred on Mars.
On Earth, biological activity leads to a change in the ratio of isotope S-34 to isotope S-32. However, a newly discovered meteorite of Martian origin exhibits ratios of these elements found only in terrestrial minerals dating from before the beginning of life on Earth. Therefore, it is unlikely that life occurred on Mars.
Each of the following, if true, would weaken the argument except:
Life forms that have a different effect on the ratio of S-34 to S-32 from that of life forms on Earth could have evolved elsewhere.
The effects of life on the ratio of S-34 to S-32 depend on a number of climatic and environmental factors with regard to which Earth and Mars differ.
The ratio of S-34 to S-32 in the meteorite is the same as that on Mars as a whole at the time that the material in the meteorite left Mars.
Relatively few terrestrial mineral samples contain S-34 and S-32 in the ratio that indicates the presence of biological activity.
The current ratio of S-34 to S-32 on Mars is different from that at the time the material in the meteorite left Mars.
Explanations
The author concludes that it's unlikely there's life on Mars.
Why? Because a newly discovered Martian meteorite has pre-life-on-Earth ratios of isotope S-34 to S-32. And, apparently, biological activity (so activity from lifeforms) here on Earth changes the ratio of S-34 to S-32 in a particular way.
In other words, our author thinks it's unlikely there's life on Mars because a rock from Mars has isotope levels more consistent to pre-life-Earth than biological-activity-Earth.
There are tons of ways we can poke holes in this, but it turns out this is a Weaken Except question. All we need to do is find an answer choice that either doesn't weaken the author's conclusion or downright strengthens it.
Let's have a look.
Nah, this isn't correct. This would totally weaken the argument, and was my initial objection to the author. If any life in the entire cosmos affects S-34:S-32 ratios differently than on Earth, the author's argument makes no sense.
Nope, also totally a weakener. If climatic changes play into the ratio differentiation, we would naturally assume they'd be different on Mars, given that Mars is a desolate wasteland with a completely different climate.
I like this. It doesn't impact the conclusion. If anything, my reaction is "Duh, one would hope the meteorite and its source have relatively the same isotope ratios." But more specifically, if the isotope ratios in the meteorite are the same as when it left Mars, what would we have to compare it to (the way we have pre- and post-life Earth ratios)? This is going to be the answer.
Nah, this weakens the argument. If relatively few Earthly mineral samples display the biological impacts on the S-34:S-32 ratios, then the ratios aren't a very effective way to gauge the presence of lifeforms.
No way. This totally weakens the argument. If the ratios are different on Mars now than they were when the meteorite left, it's totally possible that a Martian life form affected the ratios at a time when life could exist on Mars, just inconsistently with the way life affect the ratios here on Earth.
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