One passage per ACT Science section presents two or three scientists arguing about the same observation. It carries about seven questions, the most reading on the section and the least data.
Most students should do it last. It pays exactly what a fifteen-second lookup pays.
How to answer these
Read the introduction carefully. It states the observation nobody disputes. That single fact answers every 'what would all the scientists agree on' question.
Write one sentence per scientist. Their claim, not their evidence. Two lines is usually the entire passage.
Turn strengthen and weaken into a prediction test. If Scientist 1 says the light causes it, Scientist 1 predicts that filtering the light removes the effect. Then check whether the finding matches or contradicts that.
Ignore whether a statement sounds true. The only question is whether it fits the specific claim being asked about.
What the wrong answers look like
Right idea, wrong scientist. A real claim from the passage attached to the wrong person. The commonest error under time pressure.
True but irrelevant. Correct about the data and untouched by the claim in question.
Restates the shared observation. Definitely true, supports nobody, separates nothing. This is the one that catches careful readers.
Too strong. 'Proves', 'never', 'in all cases', where the scientist argued only for a tendency.
Practice questions
Four real questions from the CruxStudy bank, with the keyed answer marked and the explanation behind a click so you can try them first.
Example 1Easier
Ice cores from Greenland record a sharp cooling about 8,200 years ago. For each interval, Table 1 gives the reconstructed temperature anomaly (the difference from the long-term average), the sulfate concentration in the ice (a tracer of volcanic aerosol), the beryllium-10 concentration (which rises when solar activity is low), and the estimated freshwater input to the North Atlantic from melting ice.
Scientist 1: A large eruption injected sulfate aerosol high into the atmosphere, where it reflected sunlight away and cooled the surface for decades.
Scientist 2: An ice-dammed lake collapsed and dumped fresh water into the North Atlantic. The fresh cap slowed the overturning circulation that carries heat northward, so the region cooled.
Scientist 3: A deep minimum in the sun's output reduced the energy reaching Earth. The weaker solar wind let more cosmic rays into the atmosphere, raising beryllium-10 production.
Interval (yr before present)
Temp anomaly (°C)
Sulfate (ppb)
Be-10 (10^4 atoms/g)
Meltwater input (10^14 m3/yr)
8,400
+0.1
24
1.2
0.1
8,300
0.0
28
1.3
0.2
8,250
-0.4
190
1.4
0.4
8,200
-3.2
35
1.5
3.8
8,150
-2.6
30
1.6
2.9
8,050
-1.0
26
1.4
0.6
7,950
-0.2
25
1.2
0.2
According to Table 1, the highest sulfate concentration was recorded in the interval at:
8,400 yr before present.
8,300 yr before present.
8,200 yr before present.
8,250 yr before present. correct
Show the explanation
The sulfate column peaks at 190 ppb in the 8,250 yr row; every other row is between 24 and 35 ppb.
Example 2Medium
Granite boulders, some over 6 m across, lie scattered in low ridges across a flat limestone plain. The nearest granite bedrock is 150 km north. Table 1 lists field observations.
Geologist 1: A continental ice sheet moved south, plucked blocks from the granite, carried them frozen in and beneath the ice, and dropped them as the ice melted. The unsorted mix of clay through pebbles is glacial till, which forms when debris melts straight out of ice with no water to sort it. The parallel north-south scratches were cut by stones held in the moving ice base. The low ridges are moraines built at the ice margin.
Geologist 2: An ice-dammed lake to the north failed, sending a flood tens of meters deep across the plain that rolled and rafted the boulders south in days. The scratches were cut by cobbles dragged along the bed. The crude layering in the gravel lenses is the signature of moving water; till has no layering. The ridges are broad bars aligned with the flow.
Observation
Description
Largest boulder
6.2 m across
Nearest granite bedrock
150 km north
Scratches on limestone
Parallel, oriented north-south
Fine sediment
Clay through pebbles mixed together in most exposures
Gravel lenses
Crude layering present in 2 of 40 exposures
Boulder shape
Mostly angular, some rounded
Landforms
Low ridges 3 to 8 m high
Both geologists would agree that:
the boulders were carried to the plain from a source at least 150 km away. correct
the boulders were carried while frozen inside moving ice.
the north-south scratches were cut by stones held in the base of a glacier.
the mixed fine sediment was laid down by flowing water.
Show the explanation
Both accounts start from the fact in Table 1 that the nearest granite bedrock is 150 km north, and each proposes a way to move the boulders that distance.
Example 3Harder
Granite boulders, some over 6 m across, lie scattered in low ridges across a flat limestone plain. The nearest granite bedrock is 150 km north. Table 1 lists field observations.
Geologist 1: A continental ice sheet moved south, plucked blocks from the granite, carried them frozen in and beneath the ice, and dropped them as the ice melted. The unsorted mix of clay through pebbles is glacial till, which forms when debris melts straight out of ice with no water to sort it. The parallel north-south scratches were cut by stones held in the moving ice base, and the low ridges are moraines built at the ice margin.
Geologist 2: An ice-dammed lake to the north failed, sending a flood tens of meters deep across the plain that rolled and rafted the boulders south in days. The scratches were cut by cobbles dragged along the bed. The crude layering in the gravel lenses is the signature of moving water; till has no layering. The ridges are broad bars aligned with the flow.
Observation
Description
Largest boulder
6.2 m across
Nearest granite bedrock
150 km north
Scratches on limestone
Parallel, oriented north-south
Fine sediment
Clay through pebbles mixed together in most exposures
Gravel lenses
Crude layering present in 2 of 40 exposures
Boulder shape
Mostly angular, some rounded
Landforms
Low ridges 3 to 8 m high
Suppose further mapping confirmed that 38 of the 40 sediment exposures contain no layering of any kind. This finding would most directly:
support Geologist 2, because floods deposit sediment without layering.
weaken Geologist 2, because Geologist 2 treats layering as the signature of moving water. correct
weaken Geologist 1, because glacial till is described as layered sediment laid down by meltwater.
have no bearing on either explanation.
Show the explanation
Geologist 2 argues that water leaves layering behind, so finding that almost every exposure is unlayered removes the main support for the flood account. Geologist 1 describes till as debris melting straight out of ice with no water to sort it, so unlayered sediment is exactly what that account expects.
Example 4Medium
Granite boulders, some over 6 m across, lie scattered in low ridges across a flat limestone plain. The nearest granite bedrock is 150 km north. Table 1 lists field observations, and Figure 1 shows how many granite boulders per square kilometer were counted at five distances south of the granite bedrock.
Geologist 1: A continental ice sheet moved south, plucked blocks from the granite, carried them frozen in and beneath the ice, and dropped them as the ice melted. The unsorted mix of clay through pebbles is glacial till, which forms with no water to sort it. The parallel north-south scratches were cut by stones held in the moving ice base, and the low ridges are moraines.
Geologist 2: An ice-dammed lake to the north failed, sending a flood tens of meters deep that rolled and rafted the boulders south in days. The scratches were cut by cobbles dragged along the bed. The crude layering in the gravel lenses is the signature of moving water. The ridges are bars aligned with the flow.
Observation
Description
Largest boulder
6.2 m across
Nearest granite bedrock
150 km north
Scratches on limestone
Parallel, oriented north-south
Fine sediment
Clay through pebbles mixed together in most exposures
Gravel lenses
Crude layering present in 2 of 40 exposures
Boulder shape
Mostly angular, some rounded
Landforms
Low ridges 3 to 8 m high
Does Figure 1 support the claim, made by both geologists, that the boulders came from the north?
No, because boulder abundance is greatest 250 km from the granite and falls off toward the north.
No, because boulder abundance is the same at every distance.
Yes, because boulder abundance rises steadily with distance from the granite.
Yes, because boulder abundance is greatest closest to the granite and falls off to the south. correct
Show the explanation
Figure 1 shows the count dropping from its highest value at 150 km to its lowest at 250 km, the pattern expected if transport ran from north to south. The fall-off runs southward, not northward, and the counts are plainly not equal across the five distances.
Drill all 95 of them
Open the drill inside CruxStudy and it serves conflicting viewpoints questions one at a time, with an explanation after every answer and your accuracy tracked. Free, no account.
How do I answer 'which would all scientists agree on' questions?
The answer is in the introduction, which states the observation everyone is trying to explain. Options drawn from any one scientist's argument are what the others dispute.
Should I read conflicting viewpoints first or last?
Usually last. It is the only passage where you must read every word, and it is worth the same points as the fast lookup questions elsewhere.
How do I handle strengthen and weaken questions?
Find the prediction inside the claim, then test the finding against it. A finding that contradicts the prediction weakens; one that matches it strengthens.
CruxStudy is a college admission test prep program by CruxSci. Not affiliated with, or endorsed by, the College Board or ACT, Inc. Example questions are original CruxStudy material.