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Interior of Earth
Specifically oriented for entrance examinations
| Question | Answer |
|---|---|
| What are the five mechanical (rheological) layers of the Earth? | Lithosphere, Asthenosphere, Mesosphere (Mantle), Outer Core, Inner Core. |
| What is the main difference between lithosphere and asthenosphere? | Lithosphere is rigid and elastic; asthenosphere is semi-solid, non-rigid, and ductile due to higher temperature. |
| What is the average thickness range of oceanic and continental lithosphere? | Oceanic: ~0 to 140 km Continental: 40 to 280 km |
| What is the composition and average density of the lithosphere? | Basaltic composition; ~3.5 g/cm³ |
| Why does the asthenosphere allow plate movement? | It is weak and ductile, allowing convection currents caused by heat from the core. |
| At what depths is the asthenosphere generally found? | Between ~80 km to 200 km |
| What distinguishes the mesosphere (lower mantle) from the asthenosphere? | The mesosphere is more rigid and less mobile due to greater pressure. |
| What is the depth range of the mesosphere and its subdivisions? | ~410 km to 2900 km; upper (Gutenberg layer) and lower (Golitsyn layer). |
| What are the thicknesses of the outer core and inner core? | Outer core: ~2,300 km thick Inner core: ~1,220 km thick |
| Why is the inner core solid despite high temperatures? | Immense pressure keeps iron-nickel minerals in a solid phase. |
| What is the role of the Earth's outer core in sustaining life? | Circulating molten iron generates Earth's magnetic field, protecting the atmosphere. |
| What discontinuities separate the core layers? | Gutenberg Discontinuity (~2900 km): Mantle–Outer Core Lehmann Discontinuity (~5100 km): Outer Core–Inner Core |
| What are the three main compositional layers of the Earth? | Crust, Mantle, Core. |
| What is the volume and mass contribution of crust, mantle, and core? | Crust: ~1% volume, 0.4% mass Mantle: ~84% volume, 68% mass Core: ~15% volume, 31% mass |
| What are SIAL and SIMA layers? | SIAL: Silica and Alumina (continental crust) SIMA: Silica and Magnesium (oceanic crust) |
| What are the three layers of the oceanic crust? | Layer 1: Unconsolidated sediments (~0.4 km) Layer 2: Basaltic (Olivine tholeiites) Layer 3: Gabbroic with ultramafics (3A: isotropic, 3B: cumulate gabbro) |
| Major differences between oceanic and continental crust? | Oceanic: Layered, thinner (7 km), younger (~180 Ma), more stable Continental: Not layered, thicker (40 km), older (up to 4 Ga), tectonically active |
| What separates crust from mantle? | Mohorovičić Discontinuity (~33 km) |
| What are the compositions of upper and lower continental crust? | Upper: Granodiorite to Diorite Lower: Gabbroic and Anorthositic |
| What minerals dominate the mantle composition? | Peridotite (Olivine + <15% Garnet); Eclogite (no Olivine, ~30% Garnet) |
| What causes seismic discontinuities at 410 km and 660 km depths? | 410 km: Olivine → Spinel 660 km: Spinel → Perovskite + Periclase; Pyroxene → Garnet or Ilmenite structure |
| What is the D″ layer and its significance? | A low-velocity, high-conductivity zone at the base of the mantle (~200–300 km above core); may host mantle plumes and marks transition to outer core. |
| What do seismologists study to understand Earth’s interior? | Seismic (shock) waves produced by natural (earthquakes) or artificial (explosions) sources. |
| What major layers are identified using seismic waves? | Crust, Mantle, Liquid Outer Core, Solid Inner Core. |
| What are the two types of body waves? | P-waves (Primary) S-waves (Secondary) |
| What is the other name for P-waves and why are they called "primary"? | Compressional, longitudinal, or dilatational waves; they are the fastest and arrive first at seismic stations. |
| How do P-waves move through material? | Material compresses and expands in the direction of wave propagation. |
| What materials can P-waves travel through? | Solids, liquids, and gases (due to compressibility) |
| What factors affect P-wave velocity? | Rigidity, Compressibility, Density |
| Why can't S-waves travel through liquids or gases? | Because they require rigidity, which fluids lack. |
| What kind of motion do S-waves cause in particles? | Shear or transverse movement perpendicular to wave propagation. |
| What are Sy and SH waves? | Sy: Polarized in the vertical plane SH: Polarized in the horizontal plane |
| What distinguishes surface waves from body waves? | Travel along Earth’s surface only Slower and lower frequency More destructive, especially near the epicenter |
| What are the two types of surface waves? | Rayleigh waves and Love waves |
| What are the characteristics of Rayleigh waves? | Retrograde elliptical particle motion (vertical plane) Mix of P and SV motion Cause both vertical and horizontal ground motion |
| Why are Rayleigh waves called "rolling waves"? | Their motion resembles ocean waves, causing up–down and side–side ground motion. |
| What are the characteristics of Love waves? | Horizontal, side-to-side movement Faster than Rayleigh but slower than body waves Most destructive to buildings Only occurs when a finite layer overlays a semi-infinite medium Similar to SH waves |
| Arrange seismic waves by velocity (fastest to slowest): | Vp > Vs > VL > VR |
| Arrange seismic waves by destructiveness (most to least): | L > R > S > P |
| Which waves indicate the liquid nature of Earth's outer core? | S-waves do not pass through the outer core, confirming its liquid nature. |
| What are long-period waves and why are they called so? | Surface waves with extended wavelengths; they are lower in frequency and affect only the surface. |
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