πŸͺ¨ INTERNAL STRUCTURE OF THE EARTH World Geography Β· Ch 07

BPSC / BSSC β€” World Geography Mind Map Series

πŸ” Sources of Earth's Internal Structure

Direct Sources

  • Volcanoes
  • Drilling

Indirect Sources

  • Gravity
  • Magnetic Field
  • Meteorites
  • Seismic Waves
⚑ Quick Recall
Direct = Volcanoes & Drilling Β· Indirect = Gravity, Magnetic Field, Meteorites & Seismic Waves
🌐 Earth's Layers β€” Overview
Crust (SIAL)0–30 km
Mantle (SIMA)30–2900 km
Outer Core (NIFE β€” Liquid)2900–5150 km
Inner Core (NIFE β€” Solid)5150–6371 km
  • Crust β†’ SIAL (Silica + Aluminium)
  • Mantle β†’ SIMA (Silica + Magnesium)
  • Core β†’ NIFE (Nickel + Iron)
⚑ Quick Recall
Mnemonic β€” Crust: SIAL, Mantle: SIMA, Core: NIFE
πŸͺ¨ Crust or Lithosphere (5–30 km thick)
  • Earth's outer surface (Continental and Oceanic crust)

Continental Crust

  • ~30 km thickness
  • Thick, Light
  • Granitic composition

Oceanic Crust

  • ~5 km thickness
  • Thin / Dense
  • Basaltic composition
Two Main Parts SIAL (Silica + Aluminium) β€’ SIMA (Silica + Magnesium)
Subdivisions Upper Crust and Lower Crust
⚠ Exam Trap
"Crust" and "Lithosphere" aren't identical: the upper part of the Crust + the topmost rigid Mantle (together ~100 km) form the Lithosphere.
πŸŒ‹ Mantle
Key PointDetails
Thickness30–2900 km
Nickname"White of the Earth" (egg-yolk analogy)
CompositionFormed of basaltic rocks
AsthenosphereWeak Zone – Semi-molten β€’ ~100 km thick (plastic state)
Source of MagmaSource of magma in Volcano β†’ Magma chamber
⚑ Quick Recall
Earth β‰ˆ Egg analogy: Crust = Shell, Mantle = White, Core = Yolk
πŸ”₯ Core
Key PointDetails
Central PartNIFE – Nickel (Ni) + Iron (Fe) rich
Extent2900 km to 6371 km
Outer Core2900–5150 km β€’ Liquid state
Inner Core5150–6371 km β€’ Solid state (despite extreme temperature, due to immense pressure)
⚠ Exam Trap
Outer Core = Liquid, Inner Core = Solid β€” the inner core stays solid despite being hotter, because of the immense pressure at that depth.
πŸ§ͺ Composition / Elements of Earth's Crust
ElementPercentage (%)
Oxygen46.60
Silicon27.72
Aluminium8.13
Iron5.0
Calcium3.63
Sodium2.83
Potassium2.59
Magnesium2.09
Total (top 8 elements) Nearly 98% of the entire crust
🌍 Whole Earth β€” Element Composition
RankElementPercentage (%)
1Iron35.5
2Oxygen30.0
3Silicon15.0
4Magnesium13.0
5Nickel2.4
6Sulphur1.9
7Calcium1.1
8Aluminium1.1
⚠ Exam Trap
For the Crust, Oxygen ranks #1 (46.6%); but for the whole Earth, Iron ranks #1 (35.5%) β€” these two rankings are commonly mixed up.
πŸ”— Discontinuity
  • Transitional zone between two layers
  • Five discontinuities between Earth's layers
πŸ“ The Five Discontinuities
DiscontinuityLocation (Between)Key Feature
Conrad DiscontinuityUpper Crust and Lower CrustBetween upper and lower crust
MohorovičiΔ‡ (Moho) DiscontinuityLower Crust and Upper MantleMost significant boundary
Repetti DiscontinuityUpper Mantle and Lower Mantleβ€”
Gutenberg DiscontinuityMantle and Outer CoreMajor seismic boundary
Lehmann DiscontinuityOuter Core and Inner Coreβ€”
⚑ Quick Recall
Trick: "Koi Mujhe Roti-Gur Laado" β†’ Conrad | Moho | Repetti | Gutenberg | Lehmann
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