The internal constitution of Earth comprises concentric mechanical and compositional geospheres delineated through seismic body wave velocity profiles (compressional P-waves and shear S-waves). The outermost solid shell, the crust, represents less than 1% of planetary volume, divided into granitic continental crust (SIAL, density 2.7 g/cm³) and basaltic oceanic crust (SIMA, density 3.0 g/cm³). The crust transitions to the mantle across the Mohorovičić discontinuity at depths varying from 5 to 70 kilometers. Extending to a depth of 2,900 kilometers, the mantle encompasses 84% of Earth's volume and 67% of its mass, composed primarily of peridotitic ultramafic silicates. Its uppermost mechanical layer forms the rigid lithosphere with the crust, which glides across the ductile, partially molten asthenosphere (100 to 400 kilometers depth). The core begins at 2,900 kilometers across the Gutenberg discontinuity, dominated by an iron-nickel alloy (NIFE). It subdivides into a liquid outer core (2,900 to 5,150 kilometers), whose convective dynamo generates Earth's geomagnetic dipole while blocking transverse S-waves, and a solid inner core extending to Earth's center at 6,371 kilometers, bounded by the Lehmann discontinuity where intense pressures exceeding 330 gigapascals maintain iron in a solid crystalline state.
High-yield conceptual summaries for competitive exams and rapid revision.
Earth's internal structure is divided compositionally into the crust, mantle, and core, and mechanically into the lithosphere, asthenosphere, mesosphere, and core.
The continental crust consists primarily of granitic rocks rich in silica and alumina (SIAL) with a mean density of 2.7 g/cm³.
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.
The Conrad discontinuity separates the granitic upper continental crust from the basaltic lower continental crust.
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.
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.
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.
The Repetti discontinuity marks the transitional phase boundary between the upper mantle and the lower mantle at an approximate depth of 660 km.
The Gutenberg discontinuity, situated at 2,900 km depth, marks the boundary between the silicate lower mantle and the liquid metallic outer core.
The core constitutes approximately 16% of Earth's volume and 32% of its total mass, primarily composed of nickel and iron (NIFE).
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°.
Convective currents of molten iron and nickel in the liquid outer core generate Earth's geomagnetic field via the self-exciting geodynamo mechanism.
The Lehmann discontinuity at 5,150 km depth marks the sharp boundary separating the liquid outer core from the solid inner core.
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.
The P-wave shadow zone occurs between 105° and 142° from an earthquake epicenter due to refraction at the mantle-core Gutenberg boundary.
Which seismic boundary separates the Earth's crust from the underlying upper mantle?
Verified Explanation
The Mohorovičić discontinuity, commonly called the Moho, marks the boundary where seismic P-wave and S-wave velocities increase sharply due to the transition from crustal rocks to denser peridotitic mantle rocks. It was identified in 1909 by Croatian seismologist Andrija Mohorovičić.
2ID: GK-WGEOG-00657
mediumContinents, Oceans & Landforms
Which seismic discontinuity marks the boundary between the Earth's lower mantle and the liquid outer core at a depth of approximately 2,900 kilometers?
Verified Explanation
The Gutenberg discontinuity occurs at roughly 2,900 km beneath the Earth's surface, marking the boundary between the solid silicate lower mantle and the liquid iron-nickel outer core. At this boundary, primary seismic waves (P-waves) abruptly decrease in velocity and secondary waves (S-waves) are completely blocked, generating the S-wave shadow zone.
3ID: GK-WGEOG-00769
mediumMountain Ranges & Volcanoes
Mauna Loa on the island of Hawaii is classified as which type of volcano due to its broad, gently sloping profile formed by low-viscosity basaltic lavas?
Verified Explanation
Mauna Loa is the world's largest subaerial shield volcano, covering an estimated volume of 75,000 cubic kilometers. Its broad, dome-like topography with slopes rarely exceeding 6 to 10 degrees is constructed by successive effusive eruptions of fluid, low-silica tholeiitic basalt magma originating from the Hawaiian mantle hotspot.
4ID: GK-WGEOG-00781
mediumMountain Ranges & Volcanoes
Mount Erebus, notable for hosting one of Earth's few persistent phonolitic convecting lava lakes, is the southernmost active volcano in the world, located on which Antarctic island?
Verified Explanation
Mount Erebus (3,794 m) is situated on Ross Island in the Ross Sea, Antarctica. It is an active anorthoclase-phonolite stratovolcano that has maintained a continuous convecting magma lake in its summit crater since at least 1972. Mount Erebus is powered by an underlying mantle hotspot beneath the West Antarctic Rift System.
5ID: GK-WGEOG-00807
mediumDeserts, Plateaus & Valleys
The massive flood basalt formations comprising the Deccan Traps in western and central India were erupted as the Indian Plate drifted over which mantle plume hotspot?
Verified Explanation
The Deccan Traps are one of the largest continental flood basalt provinces on Earth, erupted around 66 million years ago near the Cretaceous-Paleogene boundary. They formed when the northward-drifting Indian Plate passed directly over the Réunion hotspot, producing over 1 million cubic kilometers of basaltic lava layers that cover more than 500,000 square kilometers.
6ID: GK-DMGT-00542
mediumEarthquakes, Seismic Zonation & Landslides
What geological term denotes the dipping planar seismic zone of deep-focus earthquakes that traces the path of an oceanic tectonic plate descending into the mantle at a subduction boundary?
Verified Explanation
The Wadati-Benioff zone, named after seismologists Kiyoo Wadati and Hugo Benioff who independently discovered it, is a planar zone of seismicity that dips into the mantle beneath an active oceanic trench. Tracing the trajectory of a cold, brittle down-going oceanic tectonic plate (such as the Indo-Australian Plate subducting beneath the Sunda Plate along the Andaman-Sumatra trench), it produces intermediate to deep earthquakes at depths up to 670 km.
7ID: GK-OCEN-00343
hardOcean Currents, Bathymetry & Marine Ecology
The Ninety East Ridge in the Indian Ocean is a 5,000-km-long linear submarine volcanic ridge created by the northward movement of the Indian Plate over which mantle hotspot?
Verified Explanation
The Ninety East Ridge is a prominent north-south oriented submarine volcanic trace on the Indian Ocean floor formed between 82 and 43 million years ago as the Indian Plate drifted over the Kerguelen mantle plume.
8ID: GK-SPCE-00699
easySolar System & Planetary Science
Which volatile-rich dwarf planet and largest body in the main asteroid belt was found by NASA's Dawn spacecraft to possess bright sodium carbonate salt deposits inside Occator Crater and an interior water-ice mantle?
Verified Explanation
Ceres is the largest object in the main asteroid belt (diameter ~940 km) and the only dwarf planet located inside the orbit of Neptune. NASA's Dawn orbited Ceres from 2015 to 2018, discovering that Ceres is a differentiated body with a rocky core and a volatile-rich crust and mantle containing up to 25% water ice. Dawn's cameras revealed dazzlingly bright faculae (bright spots) inside the 92-km Occator Crater, which spectroscopic analysis identified as sodium carbonate and ammonium chloride salts precipitated from subterranean brine percolating to the surface.
9ID: GK-ENV-00074
easyPollution Greenhouse Gases
Which renewable energy harnesses thermal heat energy naturally generated and stored within the Earth's sub-surface crust and magma mantle?
Verified Explanation
Geothermal power plants tap underground reservoirs of steam and hot water (e.g. in Iceland, the Geysers in California) to drive electric turbines.
10ID: GK-GSPC-00517
easyMars Exploration, Outer Solar System & Deep Space Probes
What instrument aboard NASA's InSight Mars lander (2018–2022) measured over 1,300 'marsquakes' to probe the internal crust, mantle, and molten core of Mars?
Verified Explanation
The SEIS instrument (Seismic Experiment for Interior Structure), provided by the French space agency CNES for NASA's InSight lander, used ultra-sensitive broadband sensors shielded by a wind dome to detect seismic waves from marsquakes and meteorite impacts, mapping the red planet's internal layers.