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

SSC / Railway / UPSC / BPSC 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 (variable thickness)~5–80 km thick
Mantle (Mg–Fe silicates)Moho–2900 km depth
Outer Core (NIFE β€” Liquid)2900–5150 km
Inner Core (NIFE β€” Solid)5150–6371 km
  • Older SIAL mnemonic: silica/alumina-rich upper continental crust
  • Mantle: mostly Mg–Fe silicate/peridotitic rock; SIMA is an older crustal simplification.
  • Core β†’ NIFE (Nickel + Iron)
⚑ Quick Recall
Older mnemonics: SIAL for upper continental crust; SIMA for mafic crustal material; NIFE for core. Mantle is mainly Mg–Fe silicate/peridotitic rock.
πŸͺ¨ Crust β€” Distinct from the Lithosphere
  • Earth's outer surface (Continental and Oceanic crust)

Continental Crust

  • Typically ~35–40 km on average; globally variable, roughly 16–80 km
  • Thick, Light
  • Granitic composition

Oceanic Crust

  • Typically ~6–7 km in deep ocean basins
  • Thin / Dense
  • Basaltic composition
Two Main Parts Older mnemonics: SIAL = silica + alumina; SIMA = silica + magnesia; not precise universal layers.
Subdivisions Upper Crust and Lower Crust
⚠ Exam Trap
Lithosphere = whole crust + topmost rigid mantle. Thickness varies; ~100 km is only a simplified value.
πŸŒ‹ Mantle
Key PointDetails
ThicknessFrom the variable-depth Moho to about 2,900 km depth
Nickname"White of the Earth" (egg-yolk analogy)
CompositionMostly solid Mg–Fe silicate rock, broadly peridotitic
AsthenosphereWeak, hot and ductile upper mantle; mostly solid, with local partial melt and variable depth/thickness
Source of MagmaMagma forms by partial melting of upper mantle and/or crust; a magma chamber is a subsurface reservoir.
⚑ 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 (%)
1Iron32.1
2Oxygen30.1
3Silicon15.1
4Magnesium13.9
5Sulphur2.9
6Nickel1.8
7Calcium1.5
8Aluminium1.4
⚠ Exam Trap
Crust: oxygen ~46.6% by mass; whole Earth: iron ~32.1% by mass.
πŸ”— Discontinuity
  • Transitional zone between two layers
  • Traditional named-boundary mnemonic; Conrad and Repetti are not universal global boundaries.
πŸ“ The Five Discontinuities
DiscontinuityLocation (Between)Key Feature
Conrad DiscontinuityUpper/lower crustal domains in some continental regionsSeen within some continental regions; not universal
MohorovičiΔ‡ (Moho) DiscontinuityLower Crust and Upper MantleMost significant boundary
Repetti DiscontinuityHistorical/regional mid-mantle reflector near ~1,000 km; not the modern upper/lower mantle boundaryβ€”
Gutenberg DiscontinuityMantle and Outer CoreMajor seismic boundary
Lehmann DiscontinuityOuter Core and Inner Coreβ€”
⚑ Quick Recall
'Cold Mountains Reveal Geological Layers' recalls the traditional names Conrad, Moho, Repetti, Gutenberg, Lehmann; Conrad and Repetti require non-universal/regional qualifications.
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