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About This Drill
ACT Science: Conflicting Viewpoints (Drill 1) is a Science practice drill covering Conflicting Viewpoints. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
ACT Conflicting Viewpoints questions present two competing scientific explanations and ask you to analyze each position. In this drill, two scientists debate the primary cause of the Permian-Triassic mass extinction, volcanic activity versus a bolide impact, and you must identify assumptions, find agreements, and evaluate hypothetical evidence.
Questions & Explanations
Scientists 1 and 2
Approximately 252 million years ago, at the end of the Permian period, Earth experienced the most severe mass extinction in its history. Roughly 96% of marine species and 70% of terrestrial vertebrate species disappeared. Geologists agree that the extinction coincided with two major events: the eruption of the Siberian Traps, a vast volcanic province in present-day Russia that released approximately 3 million km³ of lava, and widespread evidence of global warming, ocean acidification, and marine oxygen depletion (anoxia) in the rock record. The precise cause of the extinction, however, remains debated.
Scientist 1
The Permian-Triassic extinction was caused by the volcanic eruptions of the Siberian Traps. The eruptions released enormous quantities of carbon dioxide, raising global temperatures by an estimated 10°C. Warmer ocean temperatures reduced the solubility of oxygen in seawater, driving the widespread marine anoxia documented in sedimentary rocks from this period. The eruptions also released sulfur dioxide, which reacted with atmospheric water to produce acid rain, devastating terrestrial plant communities and disrupting food webs on land. As magma intruded into coal deposits and carbonate rocks, it released additional greenhouse gases, amplifying warming. Boundary sediments from the Permian-Triassic transition contain prominent mercury spikes, a well-established geochemical signature of large-scale volcanism, but show no iridium anomaly and no shocked quartz, the two hallmark indicators of an extraterrestrial impact. The gradual, step-wise pattern of species loss in the fossil record is also more consistent with a prolonged volcanic process than with a single catastrophic event.
Scientist 2
The Permian-Triassic extinction was triggered by the impact of an extraterrestrial body, an asteroid or comet, with Earth. The extraordinarily rapid rate of species loss, which in some marine sections appears to have occurred within tens of thousands of years, is more consistent with the sudden environmental disruption of a bolide impact than with the gradual effects of volcanism. Some researchers have reported the presence of fullerene molecules containing helium and argon with isotopic ratios characteristic of extraterrestrial sources in Permian-Triassic boundary sediments, suggesting an extraterrestrial contribution. Although no confirmed iridium anomaly has been found at this boundary, this absence does not rule out an impact: a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer. The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact, making volcanism a consequence rather than the cause.
Question 1. According to Scientist 1, what was the primary cause of the Permian-Triassic mass extinction?
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A) Volcanic eruptions of the Siberian Traps ✓
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B) The impact of an asteroid or comet
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C) A rapid drop in global ocean temperatures
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D) Depletion of the ozone layer by sulfur compounds
Explanation: Scientist 1 opens with the direct statement: "The Permian-Triassic extinction was caused by the volcanic eruptions of the Siberian Traps." The rest of Scientist 1's argument details the chain of effects from that volcanism: CO2 release caused warming, warming caused ocean anoxia, SO2 caused acid rain, and mercury spikes in boundary sediments confirm volcanic activity. Option B is Scientist 2's position. Options C and D are not claimed by either scientist.
Scientists 1 and 2
Approximately 252 million years ago, at the end of the Permian period, Earth experienced the most severe mass extinction in its history. Roughly 96% of marine species and 70% of terrestrial vertebrate species disappeared. Geologists agree that the extinction coincided with two major events: the eruption of the Siberian Traps, a vast volcanic province in present-day Russia that released approximately 3 million km³ of lava, and widespread evidence of global warming, ocean acidification, and marine oxygen depletion (anoxia) in the rock record. The precise cause of the extinction, however, remains debated.
Scientist 1
The Permian-Triassic extinction was caused by the volcanic eruptions of the Siberian Traps. The eruptions released enormous quantities of carbon dioxide, raising global temperatures by an estimated 10°C. Warmer ocean temperatures reduced the solubility of oxygen in seawater, driving the widespread marine anoxia documented in sedimentary rocks from this period. The eruptions also released sulfur dioxide, which reacted with atmospheric water to produce acid rain, devastating terrestrial plant communities and disrupting food webs on land. As magma intruded into coal deposits and carbonate rocks, it released additional greenhouse gases, amplifying warming. Boundary sediments from the Permian-Triassic transition contain prominent mercury spikes, a well-established geochemical signature of large-scale volcanism, but show no iridium anomaly and no shocked quartz, the two hallmark indicators of an extraterrestrial impact. The gradual, step-wise pattern of species loss in the fossil record is also more consistent with a prolonged volcanic process than with a single catastrophic event.
Scientist 2
The Permian-Triassic extinction was triggered by the impact of an extraterrestrial body, an asteroid or comet, with Earth. The extraordinarily rapid rate of species loss, which in some marine sections appears to have occurred within tens of thousands of years, is more consistent with the sudden environmental disruption of a bolide impact than with the gradual effects of volcanism. Some researchers have reported the presence of fullerene molecules containing helium and argon with isotopic ratios characteristic of extraterrestrial sources in Permian-Triassic boundary sediments, suggesting an extraterrestrial contribution. Although no confirmed iridium anomaly has been found at this boundary, this absence does not rule out an impact: a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer. The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact, making volcanism a consequence rather than the cause.
Question 2. Which of the following statements would both Scientist 1 and Scientist 2 most likely agree with?
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A) An iridium anomaly is present in Permian-Triassic boundary sediments worldwide
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B) The extinction was caused solely by gradual volcanic processes over millions of years
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C) The Siberian Traps were erupting at approximately the same time as the extinction ✓
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D) Fullerenes with extraterrestrial noble gases conclusively prove an impact occurred
Explanation: Both scientists acknowledge the Siberian Traps. Scientist 1 argues the Traps were the primary cause. Scientist 2 explicitly states "The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact" -- acknowledging the Traps were erupting, just disputing whether they were the cause. The intro paragraph also establishes this as agreed background. Option A is wrong -- Scientist 1 explicitly says there is NO iridium anomaly. Option B is Scientist 1's view only (and even S1 doesn't say "millions of years"). Option D overstates Scientist 2's claim -- S2 says only "some researchers have reported" the fullerene evidence and does not call it conclusive.
Scientists 1 and 2
Approximately 252 million years ago, at the end of the Permian period, Earth experienced the most severe mass extinction in its history. Roughly 96% of marine species and 70% of terrestrial vertebrate species disappeared. Geologists agree that the extinction coincided with two major events: the eruption of the Siberian Traps, a vast volcanic province in present-day Russia that released approximately 3 million km³ of lava, and widespread evidence of global warming, ocean acidification, and marine oxygen depletion (anoxia) in the rock record. The precise cause of the extinction, however, remains debated.
Scientist 1
The Permian-Triassic extinction was caused by the volcanic eruptions of the Siberian Traps. The eruptions released enormous quantities of carbon dioxide, raising global temperatures by an estimated 10°C. Warmer ocean temperatures reduced the solubility of oxygen in seawater, driving the widespread marine anoxia documented in sedimentary rocks from this period. The eruptions also released sulfur dioxide, which reacted with atmospheric water to produce acid rain, devastating terrestrial plant communities and disrupting food webs on land. As magma intruded into coal deposits and carbonate rocks, it released additional greenhouse gases, amplifying warming. Boundary sediments from the Permian-Triassic transition contain prominent mercury spikes, a well-established geochemical signature of large-scale volcanism, but show no iridium anomaly and no shocked quartz, the two hallmark indicators of an extraterrestrial impact. The gradual, step-wise pattern of species loss in the fossil record is also more consistent with a prolonged volcanic process than with a single catastrophic event.
Scientist 2
The Permian-Triassic extinction was triggered by the impact of an extraterrestrial body, an asteroid or comet, with Earth. The extraordinarily rapid rate of species loss, which in some marine sections appears to have occurred within tens of thousands of years, is more consistent with the sudden environmental disruption of a bolide impact than with the gradual effects of volcanism. Some researchers have reported the presence of fullerene molecules containing helium and argon with isotopic ratios characteristic of extraterrestrial sources in Permian-Triassic boundary sediments, suggesting an extraterrestrial contribution. Although no confirmed iridium anomaly has been found at this boundary, this absence does not rule out an impact: a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer. The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact, making volcanism a consequence rather than the cause.
Question 3. Which of the following findings, if confirmed, would most weaken Scientist 2's hypothesis?
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A) New analyses show that mercury concentrations spike sharply in sediments at the Permian-Triassic boundary
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B) A comprehensive global survey finds no impact crater anywhere on Earth with a confirmed age of approximately 252 million years ✓
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C) Fossil evidence confirms that marine anoxia was widespread during the late Permian
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D) Isotopic analysis reveals that ocean temperatures rose by approximately 10°C at the boundary
Explanation: Scientist 2's hypothesis requires that an extraterrestrial body struck Earth approximately 252 million years ago. A large impact event of this kind should leave a crater. If a thorough global survey confirmed no impact structure of the correct age exists anywhere on Earth -- including on the ocean floor -- this would directly undermine the physical basis of Scientist 2's claim. Option A (mercury spikes) supports Scientist 1, not weakens Scientist 2 -- but it doesn't specifically weaken the impact hypothesis since S2 has already argued that Traps volcanism may have occurred alongside or after an impact. Options C and D describe findings that both scientists already acknowledge (anoxia and warming are agreed facts in the intro) and do not bear specifically on whether an impact occurred.
Scientist 2
Approximately 252 million years ago, at the end of the Permian period, Earth experienced the most severe mass extinction in its history. Roughly 96% of marine species and 70% of terrestrial vertebrate species disappeared. Geologists agree that the extinction coincided with two major events: the eruption of the Siberian Traps, a vast volcanic province in present-day Russia that released approximately 3 million km³ of lava, and widespread evidence of global warming, ocean acidification, and marine oxygen depletion (anoxia) in the rock record. The precise cause of the extinction, however, remains debated.
Scientist 2
The Permian-Triassic extinction was triggered by the impact of an extraterrestrial body, an asteroid or comet, with Earth. The extraordinarily rapid rate of species loss, which in some marine sections appears to have occurred within tens of thousands of years, is more consistent with the sudden environmental disruption of a bolide impact than with the gradual effects of volcanism. Some researchers have reported the presence of fullerene molecules containing helium and argon with isotopic ratios characteristic of extraterrestrial sources in Permian-Triassic boundary sediments, suggesting an extraterrestrial contribution. Although no confirmed iridium anomaly has been found at this boundary, this absence does not rule out an impact: a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer. The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact, making volcanism a consequence rather than the cause.
Question 4. Scientist 2's argument depends on which of the following assumptions?
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A) The Siberian Traps did not erupt during the Permian-Triassic transition
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B) Iridium anomalies are always deposited at impact sites regardless of impactor composition
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C) A bolide impact can trigger a mass extinction without necessarily producing a detectable iridium layer ✓
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D) The fullerene evidence has been independently replicated and confirmed by multiple research groups, in Scientist 2's account
Explanation: The most prominent challenge to Scientist 2's hypothesis is the absence of an iridium anomaly at the P-T boundary -- in contrast to the well-documented iridium layer at the Cretaceous-Paleogene boundary that marks the asteroid impact linked to dinosaur extinction. Scientist 2 addresses this directly by arguing "a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer." For this response to be valid, Scientist 2 must assume that iridium absence does not rule out an impact -- i.e., that a mass-extinction-causing bolide need not leave an iridium signature. Option A is false -- Scientist 2 explicitly acknowledges the Siberian Traps were erupting. Option B is the opposite of Scientist 2's assumption. Option D is wishful thinking that Scientist 2 does not claim -- S2 specifically hedges by saying "some researchers have reported," implicitly acknowledging the evidence is not conclusively confirmed.
Scientists 1 and 2
Approximately 252 million years ago, at the end of the Permian period, Earth experienced the most severe mass extinction in its history. Roughly 96% of marine species and 70% of terrestrial vertebrate species disappeared. Geologists agree that the extinction coincided with two major events: the eruption of the Siberian Traps, a vast volcanic province in present-day Russia that released approximately 3 million km³ of lava, and widespread evidence of global warming, ocean acidification, and marine oxygen depletion (anoxia) in the rock record. The precise cause of the extinction, however, remains debated.
Scientist 1
The Permian-Triassic extinction was caused by the volcanic eruptions of the Siberian Traps. The eruptions released enormous quantities of carbon dioxide, raising global temperatures by an estimated 10°C. Warmer ocean temperatures reduced the solubility of oxygen in seawater, driving the widespread marine anoxia documented in sedimentary rocks from this period. The eruptions also released sulfur dioxide, which reacted with atmospheric water to produce acid rain, devastating terrestrial plant communities and disrupting food webs on land. As magma intruded into coal deposits and carbonate rocks, it released additional greenhouse gases, amplifying warming. Boundary sediments from the Permian-Triassic transition contain prominent mercury spikes, a well-established geochemical signature of large-scale volcanism, but show no iridium anomaly and no shocked quartz, the two hallmark indicators of an extraterrestrial impact. The gradual, step-wise pattern of species loss in the fossil record is also more consistent with a prolonged volcanic process than with a single catastrophic event.
Scientist 2
The Permian-Triassic extinction was triggered by the impact of an extraterrestrial body, an asteroid or comet, with Earth. The extraordinarily rapid rate of species loss, which in some marine sections appears to have occurred within tens of thousands of years, is more consistent with the sudden environmental disruption of a bolide impact than with the gradual effects of volcanism. Some researchers have reported the presence of fullerene molecules containing helium and argon with isotopic ratios characteristic of extraterrestrial sources in Permian-Triassic boundary sediments, suggesting an extraterrestrial contribution. Although no confirmed iridium anomaly has been found at this boundary, this absence does not rule out an impact: a cometary impactor or a low-iridium asteroid could produce catastrophic effects without depositing a detectable iridium layer. The Siberian Traps eruptions may themselves have been triggered by seismic energy released by the impact, making volcanism a consequence rather than the cause.
Question 5. A team of geologists examining deep-sea sediment cores from multiple locations around the world discovers a well-defined iridium anomaly precisely at the Permian-Triassic boundary in each core. This finding would most strongly support the hypothesis of:
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A) Scientist 1 only, because iridium is also released by volcanic eruptions
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B) Scientist 2 only, because a global iridium anomaly is a recognized signature of an extraterrestrial impact ✓
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C) Both scientists equally, because iridium is consistent with either volcanism or an impact
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D) Neither scientist, because iridium anomalies are unrelated to mass extinction events
Explanation: A global iridium anomaly at the P-T boundary would strongly support Scientist 2. Iridium is rare in Earth's crust but relatively concentrated in extraterrestrial bodies such as asteroids. A thin, globally distributed layer of iridium at a geological boundary is the key evidence that established an asteroid impact as the cause of the Cretaceous-Paleogene (K-Pg) mass extinction 66 million years ago. Scientist 1 specifically argues that the ABSENCE of an iridium anomaly supports the volcanism hypothesis and argues against an impact. Finding one would undermine a central pillar of Scientist 1's argument while directly providing the type of evidence Scientist 2's hypothesis predicts. Option A is misleading -- volcanic eruptions do not typically produce globally distributed iridium layers; the iridium signature at K-Pg is not attributed to volcanism. Option C incorrectly treats iridium as neutral evidence when it in fact strongly favors the impact hypothesis.