Key Concepts & Self-Assessment15 Key Facts
Review key Earth's Interior: Crust, Mantle, Core & Seismic Discontinuities exam facts and rate your mastery to track revision.
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#1
Earth's internal structure is divided compositionally into the crust, mantle, and core, and mechanically into the lithosphere, asthenosphere, mesosphere, and core.
#2
The continental crust consists primarily of granitic rocks rich in silica and alumina (SIAL) with a mean density of 2.7 g/cm³.
#3
The oceanic crust consists predominantly of basaltic rocks rich in silica and magnesium (SIMA) with a mean density of 3.0 g/cm³ and a thickness of 5 to 10 km.
#4
The Conrad discontinuity separates the granitic upper continental crust from the basaltic lower continental crust.
#5
The Mohorovičić discontinuity (Moho) demarcates the boundary between the base of the crust and the upper mantle, where seismic P-wave velocity jumps from 6 km/s to 8 km/s.
#6
The mantle extends from the Moho to a depth of 2,900 km, comprising approximately 84% of Earth's volume and 67% of planetary mass.
#7
The asthenosphere is a ductile, semi-fluid zone in the upper mantle between 100 km and 400 km depth that serves as the mechanical base for lithospheric plate tectonics.
#8
The Repetti discontinuity marks the transitional phase boundary between the upper mantle and the lower mantle at an approximate depth of 660 km.
#9
The Gutenberg discontinuity, situated at 2,900 km depth, marks the boundary between the silicate lower mantle and the liquid metallic outer core.
#10
The core constitutes approximately 16% of Earth's volume and 32% of its total mass, primarily composed of nickel and iron (NIFE).
#11
The liquid outer core extends from 2,900 km to 5,150 km depth and completely blocks transverse shear waves (S-waves), creating an S-wave shadow zone beyond 105°.
#12
Convective currents of molten iron and nickel in the liquid outer core generate Earth's geomagnetic field via the self-exciting geodynamo mechanism.
#13
The Lehmann discontinuity at 5,150 km depth marks the sharp boundary separating the liquid outer core from the solid inner core.
#14
The solid inner core extends from 5,150 km to the planetary center at 6,371 km depth, with temperatures exceeding 5,400°C and pressures around 330 to 360 GPa.
#15
The P-wave shadow zone occurs between 105° and 142° from an earthquake epicenter due to refraction at the mantle-core Gutenberg boundary.
Subject Specialist Commentary
Analytical perspective & practical exam advice from the Master10 academic board
Earth's interior is arranged in concentric layers identified through seismic shockwaves. Compositionally, the planet comprises an outer silicate crust, a dense semi-molten mantle extending to 2,900 kilometres, and a metallic iron-nickel core at the centre. Mechanically, the rigid lithosphere glides over the plastic, semi-fluid asthenosphere, driving continental drift. Convective churning of liquid iron in the outer core generates Earth's geomagnetic field via a geodynamo process, while extreme pressure keeps the innermost core solid despite temperatures exceeding 5,400 degrees Celsius.
Earthquake wave behaviour and internal boundary discontinuities are major question areas in competitive exams. Memorize the internal boundaries from surface to centre using the classic mnemonic C-M-R-G-L: Conrad, Mohorovičić, Repetti, Gutenberg, and Lehmann. A frequent UPSC statement trap targets seismic shadow zones: secondary transverse S-waves cannot travel through liquids, vanishing completely beyond 105 degrees from an earthquake epicentre, whereas primary P-waves refract through the core, creating a narrower shadow zone between 105 and 142 degrees.
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