Question 3·Hard·Command of Evidence
Nucleobase Concentrations from Murchison Meteorite and Soil Samples in Parts per Billion
| Nucleobase | Murchison meteorite sample 1 | Murchison meteorite sample 2 | Murchison soil sample |
|---|---|---|---|
| Isoguanine | 0.5 | 0.04 | not detected |
| Purine | 0.2 | 0.02 | not detected |
| Xanthine | 39 | 3 | 1 |
| Adenine | 15 | 1 | 40 |
| Hypoxanthine | 24 | 1 | 2 |
Employing high-performance liquid chromatography—a process that uses pressurized water to separate material into its component molecules—astrochemist Yashiro Oba and colleagues analyzed two samples of the Murchison meteorite that landed in Australia as well as soil from the landing zone of the meteorite to determine the concentrations of various organic molecules. By comparing the relative concentrations of types of molecules known as nucleobases in the Murchison meteorite with those in the soil, the team concluded that there is evidence that the nucleobases in the Murchison meteorite formed in space and are not the result of contamination on Earth.
Which choice best describes data from the table that support the team’s conclusion?
For SAT Reading and Writing data-support questions, first underline the conclusion or claim in the passage. Then ask, “What pattern in the table/graph would make this conclusion more believable?” (for example, present in one place but absent in another). Scan the visual quickly by rows and columns to find that pattern before looking closely at the answer choices, then choose the option that most directly and accurately describes the relevant data, eliminating any that misread the numbers or that would actually weaken the conclusion.
Hints
Focus on what would rule out contamination
To support “not contamination,” look for something present in the meteorite but absent in the soil from the landing zone.
Start with the soil column
Scan the soil sample column for the entries that say “not detected.” Those are your best candidates.
Confirm across both meteorite samples
For each nucleobase that’s “not detected” in soil, check whether it still has numbers (not zero/not missing) in both meteorite sample 1 and sample 2.
Step-by-step Explanation
Identify what the question is really asking
The question asks which data support the team’s conclusion. The team concludes the nucleobases in the meteorite formed in space and are not the result of contamination from Earth soil. So we need table data that make soil contamination unlikely.
Decide what pattern in the table would support that conclusion
If a nucleobase came from soil contamination, we would expect it to show up in the soil sample as well as in the meteorite.
A strong supporting pattern is:
- detected in both meteorite samples, and
- not detected in the soil sample.
That pattern suggests the nucleobase is in the meteorite but not in the local soil, making contamination less likely.
Use the table to find rows that match the pattern
First, scan the soil sample column and note which nucleobases are marked “not detected.”
Then check those same rows to see whether the nucleobase has a (nonzero) concentration in both meteorite sample 1 and meteorite sample 2.
Match the pattern to an answer choice
The table shows that isoguanine (0.5 and 0.04) and purine (0.2 and 0.02) are detected in both meteorite samples but are not detected in the soil sample. That directly supports the claim that these nucleobases were not introduced by local soil contamination.
Correct answer: Isoguanine and purine were detected in both meteorite samples but not in the soil sample.