All practice questions

A student investigates how the surface roughness of a ramp affects the distance a wooden block travels after sliding down. The student proposes the following hypothesis: 'A block will travel a shorter distance on smoother surfaces because smooth surfaces offer less frictional resistance.'

The student collects the following data:

Based on these results, which of the following represents the most accurate modification to the student's hypothesis?

Three scientists discuss the primary cause of a global cooling event that occurred millions of years ago.

Scientist 1
The cooling was caused by volcanic eruptions. Volcanic dust and sulfur dioxide gas ($SO_2$) were injected into the stratosphere. These aerosols reflected incoming solar radiation back into space, reducing global surface temperatures. The cooling caused a rapid growth in polar ice sheets, which increased the Earth's albedo (reflectivity) and led to further cooling.

Scientist 2
The cooling was caused by the rapid expansion of early forests. The growth of these plants absorbed large amounts of carbon dioxide ($CO_2$) from the atmosphere through photosynthesis. The reduction of this greenhouse gas decreased the atmosphere's ability to retain heat, leading to global cooling. Ocean temperatures dropped, which increased the amount of $CO_2$ that dissolved in the oceans, further lowering atmospheric levels.

Scientist 3
The cooling was caused by a large asteroid impact. The impact blasted massive quantities of pulverized rock and dust into the upper atmosphere, blocking sunlight for several years. This dust layer reflected solar radiation, preventing it from warming the surface. The lack of sunlight caused widespread plant die-offs and triggered a long-term cooling cycle as snow cover expanded.

Match each of the following statements with the specific scientists who would agree with that statement.

An investigator conducted a study to evaluate how different types of dissolved organic matter (DOM) influence the rate of photochemical degradation of a synthetic pesticide, Pesticide $X$, in natural sunlight. Pesticide $X$ degrades when exposed to ultraviolet (UV) light, but dissolved organic matter can either shield the pesticide from light (attenuation) or sensitize it by generating reactive oxygen species (sensitization).

*Experiment 1*
Four identical quartz tubes were prepared, each containing a $10\text{ mg/L}$ aqueous solution of Pesticide $X$. To three of the tubes, a different type of DOM (humic acid, fulvic acid, or amino acids) was added at a concentration of $5\text{ mg/L}$. The fourth tube received no DOM. All four tubes were exposed to natural sunlight for $24\text{ hours}$. The percentage of Pesticide $X$ degraded in each tube was measured. The results are shown in Table 1.

*Experiment 2*
To determine whether the degradation was driven specifically by UV light rather than thermal decomposition (since the sun also heats the samples), the investigator prepared two additional quartz tubes. Each tube contained a $10\text{ mg/L}$ aqueous solution of Pesticide $X$ and $5\text{ mg/L}$ of humic acid. One tube was exposed to sunlight (Tube 5), while the other tube was wrapped in aluminum foil to block all light and placed adjacent to the first tube in the same outdoor environment (Tube 6). After $24\text{ hours}$, the percentage of Pesticide $X$ degraded was measured. The results are shown in Table 2.

Based on the design of Experiments 1 and 2, which of the following options correctly identifies the control group for the presence of DOM in Experiment 1, and the control group for light exposure in Experiment 2, along with the correct justification for their selection?

Initiation of the Sturtian Glaciation

The Sturtian glaciation, which occurred approximately 717 million years ago, represents one of the most extreme ice ages in Earth's history, resulting in a "Snowball Earth" where ice covered nearly the entire planet. Two geologists discuss competing hypotheses for the trigger of this event.

Geologist 1
The Sturtian glaciation was initiated by the eruption of the Franklin Large Igneous Province (LIP), a massive volcanic field located in the tropics of the supercontinent Rodinia. The primary driver of cooling was the rapid chemical weathering of the freshly erupted, highly reactive basaltic rocks. Silicate weathering consumes atmospheric carbon dioxide ($CO_2$) through the reaction:

Because the Franklin LIP erupted in a warm, humid equatorial region, weathering rates were exceptionally high. This process sequestered $CO_2$ into marine carbonates at a rate that far exceeded volcanic outgassing, causing atmospheric $CO_2$ levels to plummet. The resulting reduction in the greenhouse effect cooled the planet, allowing polar ice sheets to expand and ultimately trigger a runaway ice-albedo feedback.

Geologist 2
Silicate weathering is a slow process that operates over millions of years, which is too gradual to trigger the rapid onset of a global glaciation. Instead, the glaciation was triggered by the stratospheric injection of sulfur dioxide ($SO_2$) gas during the explosive phases of the Franklin LIP eruptions. Once in the stratosphere, $SO_2$ reacted with water vapor to form highly reflective sulfate aerosols. Because these aerosols block incoming solar radiation, they caused immediate global cooling. This cooling allowed polar ice sheets to rapidly advance to a critical latitude of approximately $30^\circ$. At this point, the ice-albedo feedback became self-sustaining, driving the Earth into a global glaciation before the sulfate aerosols could settle out of the atmosphere.

Based on the passage, Geologist 1’s explanation of how the chemical weathering of the Franklin LIP initiated global cooling relies on which of the following underlying assumptions?

### Deep-Focus Earthquakes

Most earthquakes occur at depths of less than 70 km, where rocks are cold and brittle enough to fracture under stress. However, deep-focus earthquakes occur at depths between 300 km and 700 km, where high temperatures and pressures are expected to cause rocks to deform plastically (ductile flow) rather than fracture. Two scientists discuss the mechanisms responsible for these deep-focus events.

Scientist 1
Deep-focus earthquakes are caused by dehydration embrittlement. As a subducting oceanic slab sinks into the mantle, it carries hydrous minerals (such as serpentine) down with it. At depths of 300 km to 700 km, the increasing temperature and pressure cause these hydrous minerals to decompose, releasing liquid water into the surrounding rock. This released water is highly pressurized and enters pre-existing fractures, offsetting the extreme confining pressure of the mantle. This allows the rock to undergo brittle failure and slip, producing an earthquake.

Scientist 2
Deep-focus earthquakes are caused by transformational faulting, a process associated with mineral phase changes. The mantle mineral olivine normally transitions to denser phases (wadsleyite and ringwoodite) at depths greater than 410 km under thermodynamic equilibrium. However, because the core of a subducting slab is much colder than the surrounding mantle, olivine can persist in a metastable state well below its equilibrium depth. When this metastable olivine eventually transitions to the denser phases, the rapid volume reduction creates localized shear instabilities (anticracks) that propagate as a sudden brittle-like failure, triggering an earthquake.

Based on the passage, Scientist 2's explanation of deep-focus earthquakes relies on which of the following assumptions?

Scientist 1: The channels on Mars were formed by flowing liquid water. Liquid water requires a surface temperature above $0^\circ\text{C}$ and an atmospheric pressure high enough to prevent boiling. In Mars' early history, a thick carbon dioxide greenhouse atmosphere warmed the planet, allowing liquid water to exist on the surface and carve the channels.

Based on the hypothesis of Scientist 1, which of the following is an underlying assumption regarding liquid water on early Mars?

A student hypothesized that under constant light and temperature, the rate of transpiration in bean plants increases as the relative humidity of the surrounding air increases. To test this hypothesis, the student measured the transpiration rates of several identical bean plants at different relative humidity levels. The results are shown in the table below:

Based on these results, how should the student modify their hypothesis to accurately reflect the relationship between relative humidity and transpiration rate?

Trace amounts of methane ($CH_4$) have been detected in the atmosphere of Mars. Since solar ultraviolet (UV) radiation rapidly destroys atmospheric methane, its ongoing presence implies a continuous source of replenishment. Two scientists propose different mechanisms for how this methane is generated and released.

Scientist 1
The methane is biogenic, produced by methanogenic microorganisms living in liquid water aquifers deep beneath the Martian surface. These microbes survive in the warm subsurface heated by geothermal activity. During warmer Martian seasons, ground ice thaws, forming fractures through which the accumulated methane escapes into the atmosphere.

Scientist 2
The methane is abiogenic, produced by serpentinization. In this process, liquid water reacts with olivine-rich rocks deep inside the crust to produce hydrogen gas ($H_2$). This hydrogen then reacts with carbon dioxide ($CO_2$) under high temperatures and pressures to form methane. The methane is stored in subsurface ice structures called clathrates, which seasonally destabilize and release the gas.

Which of the following is an underlying assumption shared by both Scientist 1 and Scientist 2?

Two models are proposed to explain how a certain species of lizard changes its color between green and brown.

* Model 1: The color change is regulated solely by ambient temperature. At low temperatures (below $20^\circ\text{C}$), the lizards turn brown to absorb heat. At high temperatures (above $30^\circ\text{C}$), they turn green to reflect solar radiation.
* Model 2: The color change is regulated solely by background color. When on a brown background, the lizards turn brown for camouflage. When on a green background, they turn green.

Match each new experimental finding on the left to its relationship with Model 1 and Model 2 on the right.

### Passage

Cretaceous-Paleogene Extinction Theories

Two scientists discuss the primary cause of the Cretaceous-Paleogene (K-Pg) extinction event, which occurred approximately 66 million years ago.

Scientist 1

The extinction of non-avian dinosaurs and many other species was triggered by the impact of a 10-kilometer-wide asteroid. This impact released a massive dust cloud and sulfur aerosols into the stratosphere, blocking sunlight for several years. This caused a global winter and halted photosynthesis, leading to a sudden collapse of terrestrial and marine food webs. The presence of a global iridium-rich clay layer precisely at the K-Pg boundary and the Chicxulub impact crater in Mexico support this theory. The suddenness of the extinction matches the immediate catastrophic aftermath of an impact.

Scientist 2

The extinction was a gradual process driven by the eruption of the Deccan Traps, a massive volcanic province in modern-day India. Over a span of 800,000 years surrounding the boundary, these eruptions released millions of cubic kilometers of lava, along with enormous quantities of carbon dioxide ($CO_2$) and sulfur dioxide ($SO_2$). The resulting volatile emissions caused severe climate fluctuations, including periods of intense global warming and cooling, acid rain, and ocean acidification. This prolonged environmental instability degraded habitats, steadily driving species to extinction before the asteroid impact, which was merely a minor factor.

Question

Scientist 1's hypothesis regarding the primary cause of the Cretaceous-Paleogene extinction relies on which of the following implicit assumptions?

Three researchers propose conflicting explanations for the Mpemba effect (the observation that warmer water can sometimes freeze faster than colder water).

Researcher 1
The effect is primarily driven by mass loss and cooling due to evaporation. Warmer water evaporates much more rapidly than colder water, which reduces the total mass of the water sample that must be cooled and carries away a significant amount of heat (latent heat of vaporization). This mechanism requires that the container is open to the atmosphere.

Researcher 2
The effect is primarily caused by the expulsion of dissolved gases. Heating water decreases the solubility of dissolved gases (such as $O_2$ and $CO_2$), causing them to escape. Water with lower gas concentrations has higher thermal conductivity and higher convection rates, accelerating cooling. This mechanism assumes that heating alters the physical and chemical state of the water prior to cooling.

Researcher 3
The effect is driven by changes in hydrogen bonding. In warm water, stretched hydrogen bonds force the covalent $O-H$ bonds to contract and store energy. As the water cools, these bonds relax and release energy, accelerating heat transfer out of the system. This molecular mechanism does not depend on mass loss or gas expulsion, meaning the effect can occur in completely sealed containers.

Match each of the described experimental scenarios or observations to the researcher(s) whose model predicts or is supported by that outcome.

A student hypothesized that the solubility of carbon dioxide ($CO_2$) in water is directly proportional to the water temperature because higher temperatures increase the kinetic energy of the gas molecules, allowing them to interact more with water molecules and remain dissolved. The student measured the solubility of $CO_2$ in water at a constant pressure of $1.0\text{ atm}$ across several temperatures and recorded the data in the table below:

Based on the results in the table, which of the following modifications to the student's hypothesis and explanation is most appropriate?

### Passages: Origin of Hot Jupiters

Astronomers have proposed three models to explain the existence of "hot Jupiters"—giant planets with orbital periods of less than 10 days that orbit very close to their host stars.

Model 1 (In-situ Formation)
Giant planets form at their current close-in locations ($< 0.1 \text{ AU}$ from the host star). Protoplanetary disks under certain conditions can concentrate high densities of rocky and icy grains in the inner disk. This local concentration allows a solid core of approximately $10$ Earth masses ($M_{\oplus}$) to accumulate rapidly. Once the core forms, it quickly accretes gas from the surrounding disk before the disk dissipates (typically within 10 million years).

Model 2 (Disk Migration)
Giant planets cannot form close to their host stars because the high temperatures and intense stellar winds prevent the accumulation of volatile gases. Instead, they form in the outer disk ($> 5 \text{ AU}$) where volatile materials are abundant. As the planet orbits, it exerts gravitational forces on the surrounding gaseous disk, creating spiral density waves. These waves exert a net torque on the planet, causing its orbit to shrink. The planet spirals inward toward the star (Type II migration) over 1 to 5 million years, maintaining a circular orbit that remains aligned with the star's equator.

Model 3 (High-Eccentricity Tidal Migration)
Giant planets form in the cold outer disk ($> 5 \text{ AU}$). Gravitational perturbations from a distant companion star or another massive planet disrupt the giant planet's orbit, forcing it into a highly eccentric (non-circular) and highly inclined orbit. During periastron passage (closest approach to the host star), the star's strong gravity raises tidal bulges on the planet. The tidal friction converts orbital energy into thermal energy within the planet, causing the orbit to gradually shrink and circularize over hundreds of millions of years, long after the protoplanetary gas disk has dissipated.

### Matching Task
Match each new experimental finding on the left to its correct implication for the models on the right.

### Passage

The Paleocene-Eocene Thermal Maximum (PETM) Carbon Excursion

Approximately 56 million years ago, Earth experienced the Paleocene-Eocene Thermal Maximum (PETM), characterized by a rapid global temperature rise of $5^\circ\text{C}$ to $8^\circ\text{C}$ and a massive negative carbon isotope excursion (CIE), indicating a large injection of light carbon ($^{12}\text{C}$-enriched) into the ocean-atmosphere system. Three hypotheses propose different primary mechanisms for this event.

*Hypothesis 1 (Methane Hydrate Dissociation)*
Initial gradual warming, triggered by orbital variations and volcanic outgassing, warmed deep ocean currents. This warming destabilized submarine methane hydrates ($CH_4 \cdot H_2O$) trapped in continental slope sediments. The sudden release of oceanic methane ($CH_4$), which has an extremely light isotopic signature ($\delta^{13}\text{C} \approx -60\text{‰}$), led to rapid oxidation in the water column and atmosphere, converting the methane into carbon dioxide ($CO_2$). This process depleted oceanic oxygen, caused widespread ocean acidification, and amplified global warming via the greenhouse effect.

*Hypothesis 2 (Terrestrial Carbon Combustion)*
A prolonged period of severe regional drought, combined with orbitally induced seasonal extreme temperatures, lowered water tables in high-latitude peatlands. This dried out massive reservoirs of terrestrial organic matter, including peat and shallow coal deposits. Extensive, deep-burning wildfires swept across these regions, combusting vast quantities of terrestrial organic carbon ($\delta^{13}\text{C} \approx -25\text{‰}$ to $-30\text{‰}$) directly into the atmosphere as $CO_2$ and carbon monoxide ($CO$). The combustion released soot and greenhouse gases, causing rapid atmospheric warming and subsequent ocean acidification as atmospheric $CO_2$ dissolved into the surface ocean.

*Hypothesis 3 (Thermogenic Methane Generation)*
The emplacement of the North Atlantic Igneous Province (NAIP) involved large-scale intrusions of basaltic magma (sills) into organic-rich sedimentary basins, particularly Cretaceous shales. The extreme heat of the magma thermally cracked the sedimentary organic matter, generating vast quantities of thermogenic methane gas ($\delta^{13}\text{C} \approx -35\text{‰}$ to $-45\text{‰}$) and $CO_2$. These gases migrated upward through hydrothermal vent complexes, venting directly into the atmosphere and deep ocean. This rapid, crustally driven release of light carbon acidified the oceans and drove global greenhouse warming.

Based on the hypotheses presented, match each scientific proposition on the left with the correct level of support on the right.

A scientific model of a wind turbine's power output $P$ is described by the equation $P = \frac{1}{2} \rho A v^3 \eta$, where $\rho$ is the air density, $A$ is the swept area of the rotor blades ($A = \pi r^2$, where $r$ is the blade length), $v$ is the wind velocity, and $\eta$ is the turbine efficiency. Match each modification to the turbine's operating conditions or physical dimensions (on the left) with its corresponding mathematical effect on the power output $P$ (on the right), assuming all other variables remain constant.

A student hypothesized that planets located farther from the Sun have shorter orbital periods. The student gathered average orbital data for four planets:

Based on these data, how should the student modify their hypothesis?

### Passage

Researcher 1
The primary cause of the population decline of a certain frog species (*Rana temporaria*) in a woodland pond is the increasing acidity of the pond water, caused by acid rain. As the pH of the pond decreases below $6.0$, the hatching success of frog eggs drops significantly. Additionally, increased acidity dissolves protective mucosal coatings on the eggs, making them highly susceptible to lethal fungal infections. The introduction of predatory fish to the pond has no significant impact, because these fish prefer to feed on insects rather than frog tadpoles.

Researcher 2
The primary cause of the population decline is the introduction of a non-native predatory fish species to the pond. These fish feed heavily on both the frog eggs and tadpoles, preventing them from reaching adulthood. While a low pond pH (below $6.0$) does stress the frogs, it is not the main driver of the decline, as adult frogs can tolerate a wide pH range. However, low pH levels do dissolve the protective mucosal coating of the eggs, which exposes them to fungal infections. Therefore, both acidity and predation contribute to egg mortality, but predatory fish are the primary reason the population is collapsing.

### Question
Based on the viewpoints of Researcher 1 and Researcher 2, match each statement about the frog population decline to the researcher(s) who would support that statement.

### Origin of the Moon

Two scientists present opposing viewpoints on the origin of Earth's Moon.

Scientist 1
The Moon was originally an independent planetesimal that accreted in a different region of the solar nebula than Earth. As this planetesimal passed close to Earth, it was captured by Earth's gravity and pulled into a stable orbit. When two planetary bodies form in different regions of the solar system, they accrete from different reservoirs of dust and gas, which possess distinct ratios of oxygen isotopes ($^{18}\text{O}$ to $^{16}\text{O}$). Therefore, the Moon must have a different oxygen isotope ratio than Earth.

Scientist 2
The Moon formed from the debris of a collision between the young Earth and a Mars-sized protoplanet. The high energy of this impact melted and vaporized both bodies, allowing their materials to mix thoroughly before condensing. Because the debris that formed the Moon was a well-mixed blend of Earth's mantle and the impactor, the Earth and the Moon must share nearly identical oxygen isotope ratios.

Based on the passage, Scientist 1's argument relies on which of the following assumptions about the early solar nebula?

Martian Atmospheric Methane

Instruments on Mars have detected seasonal fluctuations in atmospheric methane ($CH_4$), peaking during the Martian summer. Two scientists propose differing explanations for the source and release mechanism of this methane.

Scientist 1
The seasonal methane spikes are caused by the destabilization of subsurface methane clathrates (crystalline water-based solids physically trapping methane gas). These clathrates were formed billions of years ago when Mars possessed abundant surface water. Under current Martian conditions, clathrates are only thermodynamically stable at depths of $10\text{ meters}$ or more. During the Martian summer, solar heating warms the upper regolith, sending a thermal wave downward that destabilizes the uppermost clathrates, releasing the trapped $CH_4$, which diffuses through the porous soil into the atmosphere.

Scientist 2
The methane is produced abiotically by modern serpentinization—a geochemical reaction between liquid water and olivine-rich rock. This reaction occurs in the deep crust ($>1\text{ km}$ depth) where geothermal heat keeps water liquid. The generated $CH_4$ gas accumulates in deep geologic traps. During the Martian summer, the peak gravitational tidal forces exerted by Mars's moons deform the crust, reopening micro-fractures and allowing the pressurized methane to rapidly escape to the surface.

Which of the following is an underlying assumption of Scientist 1's explanation but NOT of Scientist 2's explanation?

Instruments on Mars orbiters and rovers have detected trace amounts of atmospheric methane ($CH_4$) that exhibit seasonal fluctuations, peaking during the late summer. Three scientists propose different models to explain the source and behavior of this methane.

Scientist 1 (Biogenic Model)
Martian methane is produced by subsurface methanogenic archaea (microbes). These microbes inhabit deep hydrothermal aquifers where liquid water is stable. The archaea combine hydrogen ($H_2$) and carbon dioxide ($CO_2$) from Martian rocks and fluid reservoirs to produce $CH_4$ and water as metabolic byproducts. Because microbial metabolic rates are temperature-dependent, methane production increases during the warmer summer months, leading to the observed seasonal fluctuations in atmospheric methane levels.

Scientist 2 (Geochemical Model)
Martian methane is generated through serpentinization, an abiotic (non-biological) reaction that occurs when subsurface olivine-rich rocks react with liquid water in the presence of dissolved carbon dioxide ($CO_2$). This reaction releases $CH_4$ gas, which is initially trapped in subsurface ice lattices (clathrates). During the Martian summer, warmer surface temperatures cause thermal expansion and micro-fracturing in the overlying permafrost, allowing the trapped geologic methane to escape into the atmosphere and producing the seasonal cycle.

Scientist 3 (Exogenous Model)
Martian methane is produced on the planet's surface via the ultraviolet (UV) photolysis of organic matter. Martian dust contains organic carbon compounds delivered by carbonaceous chondrite meteorites and micrometeorites that continuously bombard the planet. When exposed to solar UV radiation, these surface organic compounds degrade, releasing $CH_4$. The seasonal variation is driven directly by changes in solar UV flux, which peaks during the Martian summer due to the tilt of the planet's rotational axis. Liquid water is not involved in this surface reaction.

Based on the models provided, match each scientific claim on the left with the correct consensus status among the three scientists on the right.