Praxis 5572

Explanation

Contact metamorphism occurs when country rock (existing rock) is heated by a nearby igneous intrusion such as a pluton or dike. The heat drives recrystallization of minerals without the need for significant directed pressure, producing a zone of metamorphic rock called a contact aureole or metamorphic aureole around the intrusion. The intensity of metamorphism decreases with distance from the heat source. Option A describes regional metamorphism, which is associated with convergent plate boundaries, high pressures, directed stress, and produces foliated rocks like schist and gneiss over broad areas. Option C describes diagenesis and lithification, the process that forms sedimentary rocks from sediments, not metamorphic rocks. Option D describes hydrothermal metamorphism, a distinct process driven by hot fluids at mid-ocean ridges, not heat from an intrusion.

Explanation

Oceanic crust is primarily mafic (basaltic), composed of minerals rich in iron (Fe) and magnesium (Mg), giving it a density of approximately 3.0 g/cm³. Continental crust is primarily felsic (granitic), rich in silicon (Si) and aluminum (Al), with a density of approximately 2.7 g/cm³. This compositional difference is the fundamental reason for the density contrast. Option B is incorrect because oceanic crust is actually thinner (5–10 km) than continental crust (30–50 km), and thickness alone does not determine intrinsic rock density. Option C is incorrect because oceanic crust forms at mid-ocean ridges (divergent boundaries), not subduction zones; subduction zones are where oceanic crust is destroyed. Option D is incorrect because oceanic crust contains very little quartz; it is continental (granitic) crust that is rich in quartz and feldspar, and quartz is actually less dense than many mafic minerals.

Explanation

Hardness is defined as a mineral's resistance to scratching, quantified using the Mohs hardness scale from 1 (softest) to 10 (hardest). On this scale: talc = 1, fluorite = 4, orthoclase feldspar = 6, and quartz = 7. This ranking correctly identifies talc as the softest and quartz as the hardest among the four minerals listed. Option B is incorrect because it identifies the property as cleavage (which describes how a mineral breaks along planes of weakness, not scratch resistance) and assigns incorrect Mohs values. Option C is incorrect because it correctly identifies the property as hardness but assigns the wrong positions to fluorite and orthoclase; fluorite is 4 and orthoclase is 6, not the reverse. Option D is incorrect because it identifies the property as luster (which describes how light reflects off a mineral surface, not scratch resistance) and assigns incorrect scale values.

Explanation

The IPCC was established in 1988 by the WMO and UNEP specifically to provide policymakers with regular scientific assessments of climate change by synthesizing peer-reviewed literature — it does not conduct original research itself. Option A describes the function of bodies like the UNFCCC and its associated agreements (e.g., the Paris Agreement), not the IPCC. Option B mischaracterizes the IPCC; monitoring networks are operated by agencies such as NOAA and WMO member organizations. Option D describes development and adaptation finance roles carried out by organizations like the Green Climate Fund, not the IPCC.

Explanation

The stratosphere, extending from approximately 12 to 50 km above Earth's surface, contains the ozone layer (concentrated between about 15–35 km). Ozone absorbs ultraviolet radiation, which heats this layer, causing temperature to increase with altitude — a temperature inversion compared to the troposphere. A: The troposphere is the lowest layer where temperature decreases with altitude and where most weather occurs; it does not contain the ozone layer. C: The mesosphere lies above the stratosphere (50–85 km) and is characterized by temperatures that decrease with altitude; it is the coldest layer of the atmosphere. D: The thermosphere lies above 85 km and does have increasing temperatures with altitude due to absorption of solar X-rays and UV, but it does not contain the ozone layer.

Explanation

Kepler's Third Law states that the square of a planet's orbital period (T²) is proportional to the cube of its semi-major axis (a³), expressed as T² ∝ a³ or, in consistent units where T is in Earth years and a is in astronomical units, T² = a³. This means planets farther from the Sun have longer orbital periods — Mars, for example, is farther from the Sun than Earth and takes about 1.88 years to complete one orbit, consistent with this law. Option B incorrectly states T ∝ a², which is not Kepler's Third Law and does not fit observed planetary data. Option C inverts the exponents (T³ ∝ a²), which is mathematically and physically incorrect. Option D contradicts the law entirely — planets farther from the Sun move more slowly and have longer orbital periods, not shorter ones; this inverse relationship is not what Kepler's Third Law describes.

Explanation

The principle of superposition, formulated by Nicolas Steno in the 17th century, states that in an undisturbed sequence of sedimentary strata, each layer is older than the one above it and younger than the one below it. This is a foundational principle of relative dating. A) Cross-cutting relationships states that a feature that cuts across another rock must be younger than the rock it cuts — this does not address vertical age ordering of strata. B) Original horizontality states that sedimentary layers are deposited in roughly horizontal positions — it addresses the original orientation of layers, not their relative age. D) Lateral continuity states that layers of sediment extend laterally in all directions until they thin out or meet a barrier — this addresses the spatial extent of layers, not their vertical age ordering.

Explanation

Wegener's original hypothesis, published in 1912, relied primarily on the jigsaw-puzzle fit of continental margins (especially South America and Africa) and the occurrence of identical fossil species such as Mesosaurus and Glossopteris on continents now separated by wide oceans. These observations suggested the continents were once joined in the supercontinent Pangaea. Option A is incorrect because the discovery of symmetric magnetic anomalies on the seafloor came decades later (Vine and Matthews, 1963) and was evidence for seafloor spreading, not part of Wegener's original argument. Option C is incorrect because seismic tomography is a modern technique that postdates Wegener and was developed with high-performance computing in the late 20th century. Option D is incorrect because GPS satellite technology was not available until the late 20th century and is a modern confirmation of plate motion, far beyond Wegener's era.

Explanation

The stratosphere extends from approximately 12 km to 50 km above Earth's surface and contains the ozone layer, which absorbs ultraviolet radiation from the Sun. This absorption causes temperatures to increase with altitude (a temperature inversion), distinguishing the stratosphere from the troposphere. A: The troposphere is the lowest layer where temperature decreases with altitude and weather occurs; it does not contain the ozone layer. C: The mesosphere lies above the stratosphere and is characterized by decreasing temperatures with altitude — temperatures reach their lowest point at the mesopause. D: The thermosphere lies above the mesosphere and has extremely high temperatures due to solar radiation absorption, but it does not contain the ozone layer.

Explanation

The principle of original horizontality, formulated by Nicolas Steno in the 17th century, states that sediments are deposited in approximately horizontal layers under the influence of gravity. Therefore, any sedimentary strata that are now tilted, folded, or inclined must have been deformed by tectonic or other geological forces after they were originally deposited. This principle is fundamental to interpreting the structural history of rock sequences. (A) This describes the principle of superposition, not original horizontality — superposition states that in an undisturbed sequence, lower layers are older than upper layers. (C) This describes the principle of lateral continuity, which addresses the lateral extent of sedimentary layers, not their original orientation. (D) This describes the concept of clastic sedimentary rock provenance, which relates to sediment source material rather than the geometry of deposition.