ACT Science : How to find conflicting viewpoints in earth and space sciences

Study concepts, example questions & explanations for ACT Science

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Example Questions

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Example Question #51 : Earth And Space Sciences

Scientists have long debated the origin of organic molecules on Earth. Organic molecules are those based on the atom carbon, which can form four distinct bonds in contrast to the fewer number allowed in most other non-metals. As a result of this property, carbon can give rise to the enormously complex molecular shapes necessary for life to arise.

Some scientists argue that organic matter was dissolved in water ice on comets, and brought to Earth early in its history. These comets crashed into the early Earth, and deposited carbon-based molecules in copious quantities to the Earth’s surface as their water melted.

In 2014, the first space probe landed on the comet 67P/Churyumov-Gerasimenko. Suppose that scientists find the following information from 5 distinct samples after landing on the comet. Each sample was taken at a single geographical location, but 5 meters deeper than the last. Sample 1 was taken at a depth of 1 meter below the surface.

Sample #

Water Ice?

Concentration of Organics

1

No

N/A

2

Yes

1 mg/L

3

No

N/A

4

Yes

4 mg/L

5

Yes

10 mg/L

These samples were compared to 5 similar samples from the surface of Mars. Scientists posited that this comparison would be meaningful because we know that life does not exist on Mars the same way that it does on Earth. Thus, they are comparing a known non-biological celestial body, Mars, with another celestial body, the comet, which may be seeding life on suitable plants.

Sample #

Water Ice?

Concentration of Organics

1

No

N/A

2

No

N/A

3

No

N/A

4

No

N/A

5

Yes

1 mg/L

The atmosphere on Earth protects the surface from damaging radiation that is abundant in space. Comets lack this atmosphere, and radiation is known to be capable of breaking bonds in complex molecules like organics. Suppose a scientist suggests that no organic molecules could survive the radiation that they would experience on a comet, and thus the measurements in the passage must be due to contamination. Which of the following findings would most directly refute this scientist's claim?

Possible Answers:

Early organics did not exist until after the atmosphere on Earth was thick enough to protect them from radiation.

Experiments show that organics break down very quickly when exposed to even mild doses of radiation.

The depths of the sampling on the comet would not be sufficient to shield organic molecules from radiation damage.

Early organics are known to have existed on Earth when its atmosphere was too thin to protect against radiation.

Correct answer:

Early organics are known to have existed on Earth when its atmosphere was too thin to protect against radiation.

Explanation:

The scientist in the question is essentially asserting that there are no organics on the comet, and the measurements are an error. Further, he is specifically asserting that this is would be a consequence of, if nothing else, radiation damage. If organics could exist on the early Earth without a protective atmosphere, that would suggest that his assertion is incorrect.

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