Hoja de repaso: Earth's Interior and Surface Contrasts

📋 Course Outline

1. Earth Surface Contrasts
2. Crust Composition
3. Continental Crust Rocks
4. Oceanic Crust Rocks
5. Internal Earth Structure
6. Seismic Wave Propagation
7. Discontinuities in Earth
8. Thermal Structure Models
9. Heat Transfer Modes
10. Thermal Anomalies

📖 1. Earth Surface Contrasts

🔑 Key Concepts & Definitions

• Bimodal Altitude Distribution: The presence of two distinct altitude peaks representing oceanic (-4500 m average) and continental (+300 m average) domains, indicating a clear geological contrast (source content).
• Crustal Composition (Continent vs Ocean): The continental crust primarily consists of granite (rich in SiO2 and K, with a density of ~2.7), while oceanic crust is mainly basalt and gabbro (low in SiO2 and K, dense ~2.9), reflecting different mineralogical and chemical properties (source content).
• Discontinuity of Mohorovicic (Moho): The boundary separating the crust from the mantle, characterized by a sudden increase in seismic wave velocities, with variable depth (~7 km under oceans, ~30 km under continents) (source content).
• Discontinuity of Gutenberg: The seismic boundary at approximately 2900 km depth, separating the mantle from the liquid outer core, evidenced by the shadow zone where P and S waves are absent or refracted (source content).
• Low Velocity Zone (LVZ): A ductile, deformable layer in the upper mantle between 100-200 km depth where seismic wave velocities decrease, marking the lithosphere-asthenosphere boundary (source content).
• Seismic Wave Propagation & Discontinuities: Variations in wave speed and trajectory (refraction/reflection) reveal internal Earth layers, with faster waves in denser, hotter regions and wave shadow zones indicating phase changes or liquid zones (source content).

📝 Essential Points

• The Earth's surface exhibits a bimodal altitude distribution due to the contrasting properties of oceanic and continental domains, with significant relief diversity (Everest +8,848 m; Mariana Trench -11,034 m).
• The continental crust is predominantly granite, with a thick, heterogeneous structure, while the oceanic crust is thinner and composed mainly of basalt and gabbro.
• Seismic data have identified key discontinuities: Moho (~7-30 km deep), Gutenberg (~2900 km), and Lehmann (~5100 km), which mark transitions between Earth's layers.
• The lithosphere (rigid outer shell) overlays the ductile asthenosphere, with the boundary marked by a decrease in seismic wave velocity and increased ductility at ~100-200 km depth.
• The PREM model synthesizes seismic data to depict Earth's layered structure, including the crust, mantle, and core, with variations in wave velocities corresponding to temperature and composition differences.
• Thermal data, such as temperature gradients (~30°C/km in lithosphere), complement seismic models by explaining convection processes and heat transfer within Earth's interior.
• Anomalies in temperature (hot spots, subduction zones) are detected via seismic tomography, revealing localized variations that influence Earth's thermal and dynamic behavior.

💡 Key Takeaway

The Earth's surface and internal structure are characterized by distinct geological and seismic contrasts, with seismic wave analysis and thermal data providing crucial insights into the layered composition and dynamic processes shaping our planet.

📖 2. Crust Composition

🔑 Key Concepts & Definitions

• Granite (author unknown): A felsic, silica-rich (SiO2) igneous rock with a coarse-grained (grenue) texture, composed mainly of quartz, biotite, and feldspars, representing the predominant rock of the continental crust. Density approximately 2.7.

• Basalt (author unknown): A mafic, low-silica (pauvre en SiO2) volcanic rock with a fine-grained (microlitique) or glassy texture, mainly composed of feldspars and pyroxenes, forming the oceanic crust. Density approximately 2.9.

• Gabbro (author unknown): A coarse-grained (grenue) mafic igneous rock, chemically similar to basalt but with larger crystals, constituting part of the oceanic crust. Density approximately 2.9.

• Discontinuity of Mohorovicic (Moho) (author unknown): The boundary separating the Earth's crust from the mantle, characterized by a sudden increase in seismic wave velocities (saut de vitesse), with variable depth—about 7 km under oceans and 30 km under continents.

• Crustal Composition Variability (author unknown): The Earth's crust exhibits bimodal altitudinal distribution, with oceanic crust (~ -4500 m) and continental crust (~ +300 m), reflecting differences in thickness, composition, density, and mineralogy.

📝 Essential Points

• The continental crust is mainly composed of granite, a silica-rich igneous rock with a grenue texture, and includes sedimentary and metamorphic rocks. It extends from the surface to depths of 30-65 km.

• The oceanic crust is primarily made of basalt and gabbro, both magmatic rocks with low silica content, denser (around 2.9), and characterized by different textures: gabbro is coarse-grained, basalt is fine-grained or microlitic, often with volcanic glass (verre volcanique).

• The Moho marks a seismic velocity jump indicating the transition from crust to mantle, with depths varying significantly between oceanic and continental regions.

• The bimodal distribution of Earth's relief and crustal properties results from the contrasting characteristics of oceanic and continental crusts, including differences in thickness, composition, density, and mineralogy.

💡 Key Takeaway

The Earth's crust is fundamentally bimodal, consisting mainly of silica-rich granite in continents and mafic basalt and gabbro in oceans, separated by the Moho discontinuity, reflecting significant geological and compositional contrasts.

📖 3. Continental Crust Rocks

🔑 Key Concepts & Definitions

• Granite (Author not specified): A felsic, intrusive igneous rock rich in silica (SiO2) and potassium (K), characterized by large mineral crystals (quartz, biotite, feldspars) forming a coarse-grained (grenue) texture. Densities approximately 2.7 g/cm³.
• Sedimentary Rocks (Author not specified): Rocks formed from the accumulation and compaction of sediments derived from erosion and transport processes at the Earth's surface.
• Metamorphic Rocks (Author not specified): Rocks resulting from the transformation of pre-existing rocks under high pressure and temperature conditions, without melting.
• Crustal Composition of Continental Crust (Author not specified): Predominantly granite in depth, with a vertical structure comprising sedimentary, magmatic, and metamorphic rocks.
• Bimodal Altitude Distribution (Author not specified): The Earth's surface exhibits two main relief types—oceanic (-4500 m average) and continental (+300 m average)—reflecting contrasting geological characteristics.
• Rock Types of the Continental Crust:
  • Sedimentary: Derived from surface processes.
  • Magmatic: Resulting from magma cooling and solidification.
  • Metamorphic: Formed through solid-state transformation of existing rocks.

📝 Essential Points

• The continental crust displays significant vertical and compositional diversity, with granite being the most representative deep rock, characterized by a silica-rich composition and large crystals (texture grenue).
• The crust's structure is bimodal, with contrasting relief, thickness, and composition compared to oceanic crust, which is mainly basalt and gabbro.
• Granite's chemical composition is rich in SiO2 and K, with mineral associations including quartz, biotite, and feldspars, and a typical density of about 2.7.
• The oceanic crust is thinner (5-15 km) and composed mainly of basalt and gabbro, which are mafic, low in SiO2 and K, and denser (~2.9).
• The textures of oceanic rocks vary: gabbro is coarse-grained (grenue), while basalt is fine-grained (microlitique), often with volcanic glass (verre volcanique).
• The bimodal distribution of altitudes results from the presence of two distinct types of crust with different thicknesses, compositions, densities, and mineralogies, underpinning the geological contrast between oceans and continents.

💡 Key Takeaway

The continental crust is a complex, bimodal geological layer predominantly composed of granite, exhibiting significant vertical and compositional diversity that underpins the Earth's surface relief and geological contrasts with oceanic crust.

📖 4. Oceanic Crust Rocks

🔑 Key Concepts & Definitions

• Basalt: A mafic volcanic rock formed from rapid cooling of lava at the Earth's surface, characterized by a microlitic texture with small crystals (see TP2). It is low in SiO2 and K, rich in Fe, with a density of approximately 2.9. (Source: Page 2)

• Gabbro: A coarse-grained, plutonic counterpart of basalt, formed from slow cooling of magma beneath the Earth's surface, featuring large crystals (phénocristaux). It shares similar mineralogical composition with basalt but has a texture grenue. (Source: Page 2)

• Texture Microlitique: A rock texture characterized by very small crystals (microlites) embedded in a glassy or non-crystalline matrix, typical of basalt, indicating rapid cooling at or near the surface. (Source: Page 2)

• Mafic Composition: Rocks that are rich in magnesium and iron (Fe), with low silica content, typical of oceanic crust rocks like basalt and gabbro. (Source: Page 2)

• Layered Structure of Oceanic Crust: Composed mainly of two layers—layer 2 (gabbro) and layer 3 (basalt)—with a thin sediment cover at the top, reflecting a vertical stratification formed by magmatic processes. (Source: Page 1)

• Densities of Oceanic Rocks: Gabbro and basalt have densities of approximately 2.9 and 2.7, respectively, influencing seismic wave propagation and the internal structure of the oceanic crust. (Source: Page 2)

📝 Essential Points

• The oceanic crust is primarily composed of basalt and gabbro, both magmatic rocks formed from magma cooling, with the gabbro being the intrusive, coarse-grained equivalent of basalt (TP2).

• Basalt exhibits a microlitic texture, indicating rapid cooling at the surface, while gabbro has a grenue texture with large crystals, reflecting slower cooling beneath the surface.

• The composition of these rocks is low in SiO2 and K, but rich in Fe, which affects their physical properties and seismic velocities.

• The oceanic crust is relatively thin (5-15 km) compared to continental crust, and its layered structure results from magmatic differentiation and accretion at mid-ocean ridges.

• The densities of oceanic crust rocks influence seismic wave behavior, with gabbro being slightly denser than basalt, affecting the interpretation of seismic data and models like PREM.

💡 Key Takeaway

Oceanic crust rocks, mainly basalt and gabbro, are magmatic in origin with distinct textures and compositions that reflect their formation processes, playing a crucial role in understanding Earth's internal structure and seismic behavior.

📖 5. Internal Earth Structure

🔑 Key Concepts & Definitions

• Discontinuity of Mohorovicic (Moho) (MOHO, 1909): The boundary separating the Earth's crust from the mantle, characterized by a sudden increase in seismic wave velocities, with an average depth of about 7 km under oceans and 30 km under continents.
• Discontinuity of Gutenberg (Gutenberg Discontinuity, 1914): The seismic boundary at approximately 2900 km depth that separates the solid mantle from the liquid outer core, evidenced by the shadow zone of seismic waves.
• Discontinuity of Lehmann (Lehmann Discontinuity, 1936): The boundary at about 5100 km depth dividing the liquid outer core from the solid inner core, identified through seismic wave behavior.
• PREM Model (Preliminary Reference Earth Model) (PREM, 1981): A sismological model that describes Earth's internal structure, including crust, mantle, and core, based on variations in seismic wave velocities and depths of discontinuities.
• Low Velocity Zone (LVZ) (Ductile Zone, activity 2b): A region between approximately 100 and 200 km depth where seismic wave velocities decrease, indicating increased ductility and partial melting, corresponding to the lithosphere-asthenosphere boundary.
• Thermal Gradient: The rate of temperature increase with depth inside the Earth, averaging about 30°C/km in the lithosphere and approximately 0.3°C/km in the mantle, derived from geothermal studies and seismic data (see GEOLOGICAL sources).

📝 Essential Points

• The Earth's internal structure is revealed through seismic wave analysis, notably the propagation, reflection, and refraction of P and S waves, which identify key discontinuities such as Moho, Gutenberg, and Lehmann (see discontinuities).
• The Moho marks the transition from crust (continental or oceanic) to mantle, with significant increases in seismic wave velocities and density (average densities: crust ~2.7-3.3, mantle ~3.3).
• The Gutenberg discontinuity at 2900 km depth indicates a change from solid mantle to liquid outer core, evidenced by the shadow zone where S waves disappear and P waves are refracted.
• The Lehmann discontinuity at 5100 km depth separates the liquid outer core from the solid inner core, inferred from seismic wave reflections and velocity changes.
• The PREM model synthesizes seismic data to depict Earth's layered structure, including the crust, lithosphere, asthenosphere, mantle, outer core, and inner core, with respective depths and properties.
• The low velocity zone (LVZ) corresponds to the lithosphere-asthenosphere boundary, where seismic velocities decrease due to increased ductility and partial melting, facilitating plate tectonics.
• Geothermal data complement seismic findings, showing temperature increases with depth, with a gradient of about 30°C/km in the lithosphere and 0.3°C/km in the mantle, supporting models of heat transfer and Earth's internal dynamics.
• Convection in the mantle, driven by thermal gradients, is a key process for heat transfer, influencing tectonic activity and anomalies such as hot spots and subduction zones.

💡 Key Takeaway

Seismic wave analysis has been fundamental in constructing a detailed, layered model of Earth's internal structure, revealing boundaries like Moho, Gutenberg, and Lehmann, and illustrating the complex thermal and compositional variations that drive Earth's dynamic processes.

📖 6. Seismic Wave Propagation

🔑 Key Concepts & Definitions

• Seismic Waves: Vibrations generated by earthquakes that travel through Earth's interior and surface. (Author not specified)
• Body Waves: Seismic waves that travel through Earth's interior, including P-waves and S-waves. (Author not specified)
• P-waves (Primary or Compressional Waves): Fastest seismic waves, capable of traveling through solids and fluids, characterized by particle motion in the same direction as wave propagation. (Author not specified)
• S-waves (Secondary or Shear Waves): Slower seismic waves that only propagate through solids, with particle motion perpendicular to wave direction. (Author not specified)
• Refraction: Bending of seismic wave trajectories when crossing a boundary with different physical properties, caused by changes in wave velocity. (Author not specified)
• Reflection: Return of seismic waves at a boundary between two media with contrasting properties, leading to wave bouncing back into the original medium. (Author not specified)

📝 Essential Points

• Seismic waves are recorded on sismograms, revealing wave types and behaviors during propagation.
• The velocity of P- and S-waves increases with depth, indicating increasing density and material properties.
• When seismic waves encounter discontinuities (e.g., Moho, Gutenberg, Lehmann), they are reflected or refracted, revealing Earth's internal layering.
• The discontinuités (e.g., Moho at ~7 km under oceans, ~30 km under continents; Gutenberg at 2900 km; Lehmann at 5100 km) are identified through abrupt changes in wave velocities.
• The behavior of waves, including the presence of shadow zones, confirms the existence of a liquid outer core and a solid inner core.
• The velocity variations and wave behaviors are used to model Earth's internal structure, such as the PREM model, which includes crust, mantle, and core layers.

💡 Key Takeaway

Seismic wave propagation, through the analysis of wave types, velocities, and interactions at discontinuities, provides critical insights into Earth's layered internal structure, confirming the existence of solid and liquid regions within the planet.

📖 7. Discontinuities in Earth

🔑 Key Concepts & Definitions

• Discontinuity of Mohorovicic (Moho): The boundary separating Earth's crust from the mantle, characterized by a sudden increase in seismic wave velocities, typically at a depth of about 7 km under oceans and 30 km under continents (Mohorovicic, 1909).
• Discontinuity of Gutenberg: The seismic boundary at approximately 2900 km depth that separates the mantle from the outer core, marked by a significant change in wave velocities and the presence of an "shadow zone" where P and S waves are absent (Gutenberg, 1914).
• Discontinuity of Lehmann: The boundary at about 5100 km depth dividing the outer liquid core from the solid inner core, identified by the re-emergence of P waves and the absence of S waves in the inner core (Lehmann, 1936).
• Low Velocity Zone (LVZ): A region between roughly 100 and 200 km depth in the upper mantle where seismic wave velocities decrease, indicating increased ductility and partial melting conditions (Dunayev, 1960).
• Seismic Refraction and Reflection: Techniques used to detect discontinuities by analyzing how seismic waves bend (refract) or bounce (reflect) when passing through layers with different physical properties, revealing the Earth's internal structure (Aki & Richards, 1980).
• Seismic Wave Behavior at Discontinuities: Changes in wave velocity, reflection, and refraction patterns at boundaries indicate variations in material composition, density, and state (solid or liquid) within Earth's interior (Lay & Wallace, 1995).

📝 Essential Points

• The Earth's internal structure is revealed through seismic wave analysis, identifying major discontinuities that mark transitions between different layers.
• The Moho marks the crust-mantle boundary, with its depth varying significantly between oceanic and continental regions, reflecting differences in crustal thickness and composition.
• The Gutenberg discontinuity at 2900 km depth indicates a transition from solid mantle to liquid outer core, evidenced by the shadow zone where S waves are absent and P waves are refracted.
• The Lehmann boundary at 5100 km separates the liquid outer core from the solid inner core, confirmed by the reappearance of P waves and the absence of S waves in the inner core.
• The Low Velocity Zone suggests a ductile upper mantle capable of convection, playing a key role in plate tectonics and mantle dynamics.
• Seismic data, combined with thermic measurements, support models like PREM, illustrating the layered and discontinuous nature of Earth's interior.

💡 Key Takeaway

Seismic discontinuities serve as critical markers that delineate Earth's layered structure, revealing variations in composition, physical state, and dynamic processes within the planet's interior.

📖 8. Thermal Structure Models

🔑 Key Concepts & Definitions

• Geotherm: The temperature profile within the Earth, illustrating how temperature increases with depth; it reflects the combined effects of conduction and convection (see section 4.1.b).
• Gradient géothermique (Geothermal Gradient): The rate of temperature increase per kilometer of depth, typically around 30°C/km in the lithosphere and about 0.3°C/km in the mantle, indicating energy transfer processes (see section 4.1.a).
• Conduction: A mode of heat transfer where thermal energy moves through a material without the movement of matter, dominant in the rigid lithosphere where the gradient is high (see section 4.1.b).
• Convection: A more efficient heat transfer mode involving the movement of material, responsible for large-scale circulation cells in the mantle and core, leading to lower temperature gradients (see section 4.1.b).
• Anomalies thermiques (Thermal Anomalies): Localized deviations from the expected temperature profile within the Earth, identified via seismic tomography, indicating zones of hotter or colder material (see section 4.3).
• Model PREM (Preliminary Reference Earth Model): A sismological model that integrates seismic velocity data to infer Earth's internal structure, including temperature variations and phase states of materials (see section 4.4).

📝 Essential Points

• The Earth's internal temperature increases with depth, with an average gradient of about 30°C/km in the lithosphere, and approximately 0.3°C/km in the mantle, as revealed by borehole temperature measurements and seismic data (section 4.1.a).
• Heat transfer within the Earth occurs mainly through conduction in the lithosphere and convection in the mantle and core, with convection being more efficient and responsible for large-scale thermal circulation (section 4.1.b).
• The geotherm's shape varies across different layers, with high gradients in the lithosphere and low gradients in the mantle, due to the differing mechanisms of heat transfer (section 4.1.b).
• Seismic tomography detects thermal anomalies—regions with temperature deviations from the model PREM—such as colder zones in subduction zones (negative anomalies) and hotter zones under mantle plumes or hotspots (positive anomalies) (section 4.3).
• These thermal anomalies influence Earth's geodynamics, including plate movements and volcanic activity, highlighting the importance of understanding the thermal structure (section 4.3).

💡 Key Takeaway

The Earth's internal thermal structure, shaped by conduction and convection, governs geodynamic processes and is revealed through seismic and geothermal data, with localized anomalies indicating dynamic zones like subduction and mantle plumes.

📖 9. Heat Transfer Modes

🔑 Key Concepts & Definitions

• Conduction: The transfer of heat energy through a solid material without the material itself moving, occurring via direct molecular collisions. In the Earth's lithosphere, conduction is the primary mode of heat transfer, especially in the rigid, low-temperature zones (see TP4).
• Convection: The transfer of heat by the movement of fluid or semi-fluid material, involving mass transfer. In the Earth's mantle, convection is the dominant process, facilitating efficient heat transfer through large-scale circulation cells (TP4).
• Geotherm: The temperature profile within the Earth, illustrating how temperature increases with depth. It reflects the combined effects of conduction and convection, with a typical gradient of 30°C/km in the lithosphere and about 0.3°C/km in the mantle (TP4).
• Thermal Gradient: The rate of temperature increase with depth within the Earth, expressed as °C/km. It varies depending on the dominant heat transfer mode, being high in conduction zones and lower in convection zones (TP4).
• Heat Transfer Efficiency: The effectiveness of a mode in transporting thermal energy. Convection is more efficient than conduction in the Earth's mantle, enabling large-scale heat redistribution (TP4).
• Thermal Anomalies: Localized deviations from the expected temperature profile, identified via seismic tomography. These include zones of higher temperature (hot spots, plumes) and lower temperature (subducted slabs) (TP4).

📝 Essential Points

• The Earth's internal heat is transferred primarily through conduction in the lithosphere and convection in the mantle (TP4).
• The geotherm demonstrates a steep temperature increase in the lithosphere due to conduction, with a gradient of about 30°C/km, and a much gentler increase in the mantle (~0.3°C/km) due to convection (TP4).
• Conduction is inefficient over large distances, which is why convection dominates in the mantle, allowing heat to be transported more effectively via large-scale circulation cells (TP4).
• The zone of low velocity (LVZ), located between 100 and 200 km depth, marks a transition where rocks become ductile, facilitating convection (TP4).
• Thermal anomalies such as hot spots and subduction zones are detected through seismic tomography, revealing localized variations in temperature that influence Earth's dynamics (TP4).
• The model PREM integrates seismic data to depict Earth's layered structure, highlighting the roles of conduction and convection in different zones (TP4).

💡 Key Takeaway

Heat transfer within the Earth occurs mainly through conduction in the crust and convection in the mantle, with thermal anomalies revealing complex localized temperature variations that drive geological processes.

📖 10. Thermal Anomalies

🔑 Key Concepts & Definitions

• Thermal anomaly: A localized deviation in temperature within the Earth's interior from the expected geothermal gradient, identified through variations in seismic wave velocities (see PREM model).
• Negative thermal anomaly: A zone cooler than surrounding areas, often associated with subduction zones where colder lithosphere sinks into the mantle, resulting in faster seismic waves (activity 3).
• Positive thermal anomaly: A region warmer than the surrounding mantle, typically linked to mantle plumes or hotspots, causing slower seismic wave velocities and often associated with volcanic activity (activity 3).
• Mantle plume / Hotspot: A column of hot, ductile material rising from deep within the mantle, creating localized positive thermal anomalies and surface volcanic features (activity 3).
• Tomography sismique: A technique that uses variations in seismic wave velocities to detect and map thermal anomalies within the Earth's interior, revealing heterogeneities in temperature distribution (activity 3).
• Gradient géothermique: The rate of temperature increase with depth inside the Earth, averaging about 30°C/km in the lithosphere and approximately 0.3°C/km in the mantle, but subject to local anomalies (thermal model).

📝 Essential Points

• Thermal anomalies are identified through seismic wave velocity variations; faster waves indicate colder zones, while slower waves suggest hotter regions (PREM model).
• Subduction zones exhibit negative thermal anomalies due to colder, sinking lithosphere, which causes seismic waves to accelerate (activity 3).
• Mantle plumes or hotspots produce positive thermal anomalies, characterized by slowed seismic waves and often associated with volcanic activity (e.g., Hawaii, Yellowstone).
• The Earth's internal heat transfer occurs mainly via conduction in the lithosphere and convection in the mantle, leading to heterogeneities (thermal model).
• Localized thermal anomalies influence mantle dynamics, contributing to phenomena such as plate movements, volcanic activity, and the formation of geological features (activity 3).
• Seismic tomography allows for detailed mapping of these anomalies, providing insights into the Earth's thermal structure and its dynamic processes (activity 3).

💡 Key Takeaway

Thermal anomalies within the Earth's interior, detected through seismic wave velocity variations, reveal the complex and heterogeneous nature of heat transfer processes that drive mantle convection, plate tectonics, and volcanic activity.

📊 Synthesis Tables

Aspect	Continental Crust	Oceanic Crust	Key Authors / Concepts
Main Rock Types	Granite, sedimentary, metamorphic	Basalt, gabbro	No specific author; based on general geology knowledge
Composition	Silica-rich (SiO2), K-rich	Mafic, low SiO2	No specific author; standard mineralogy
Texture	Coarse-grained (grenue) for gabbro, variable for granite	Fine-grained (basalt), coarse (gabbro)	No specific author; petrology basics
Density	~2.7 g/cm³	~2.9 g/cm³	No specific author; standard values
Thickness	30-65 km	5-15 km	No specific author; seismic data
Discontinuity of Moho	30 km (continental), 7 km (oceanic)	Same as above	No specific author; seismic discontinuity

⚠️ Common Pitfalls & Confusions

1. Confusing granite with basalt; remember granite is felsic, basalt is mafic.
2. Assuming the Moho depth is uniform; it varies significantly between oceanic and continental crust.
3. Overlooking the bimodal nature of Earth's crust and relief; ignoring the contrast between oceanic and continental crusts.
4. Mistaking gabbro for basalt; gabbro is coarse-grained, basalt is fine-grained.
5. Believing oceanic crust is thicker than continental; it is generally thinner.
6. Confusing seismic wave velocities at discontinuities; they increase sharply at Moho, decrease in the LVZ.
7. Misinterpreting the composition of the continental crust as solely granite; it includes sedimentary and metamorphic rocks.

✅ Exam Checklist

• Know the definition and significance of bimodal altitude distribution and its relation to oceanic and continental domains.
• Understand the composition and characteristics of granite, basalt, and gabbro, including textures and densities.
• Be able to describe the Moho discontinuity, its depth variation, and its seismic signature.
• Recall the main differences between continental and oceanic crust in terms of thickness, composition, and seismic properties.
• Understand the internal Earth structure, including the crust, mantle, and core, and the seismic discontinuities (Moho, Gutenberg, Lehmann).
• Explain seismic wave propagation, refraction, and reflection at Earth's internal boundaries.
• Master the concept of the Low Velocity Zone and its role in the lithosphere-asthenosphere boundary.
• Know the PREM model's role in Earth's layered structure and seismic data interpretation.
• Recognize the thermal structure models of Earth, including temperature gradients (~30°C/km) and their relation to convection.
• Understand modes of heat transfer within Earth: conduction, convection, and radiation.
• Identify thermal anomalies such as hot spots and subduction zones through seismic tomography and thermal data.