The Earth’s surface configuration is shaped by a continuous interaction of endogenic and exogenic processes. Since direct access to deep interior is impossible, knowledge about internal structure is derived through indirect evidences. Understanding interior dynamics is crucial to explain earthquakes, volcanoes, tsunamis and landscape evolution.
Surface rocks and samples from mining operations, though limited to 3–4 km due to high temperatures.
Deep drilling programmes (Deep Ocean Drilling Project, Integrated Ocean Drilling Program).
Kola Superdeep Borehole reaching ~12 km depth.
Volcanic eruptions provide magma/lava samples from deep zones.
Temperature, pressure and density gradients inferred from behaviour of matter with depth.
Meteorites, assumed to be similar in composition to early Earth material.
Gravity anomalies reveal heterogeneous mass distribution within crust.
Magnetic surveys indicate magnetic mineral concentration.
Seismic wave behaviour is the most powerful tool, revealing layering and state (solid/liquid) of materials.
A sudden release of energy from the Earth’s crust along a fault, generating seismic waves.
Focus (Hypocentre): point of energy release inside Earth.
Epicentre: point on surface directly above the focus.
Body Waves
P-waves: fastest, compressional, travel through solids + liquids.
S-waves: transverse, travel only through solids; their absence in certain regions proves liquid outer core.
Surface Waves
Travel along crust; most destructive.
Speed increases with density.
Waves reflect and refract at boundaries → used to infer internal layering.
Certain distances from the epicentre record no waves.
S-wave shadow zone: beyond 105° (global), proving liquid outer core.
P-wave shadow zone: 105°–145°, indicating sharp density change at core–mantle boundary.
Tectonic (most common; due to fault movement).
Volcanic (associated with volcanic regions).
Collapse earthquakes (underground mines).
Explosion earthquakes (chemical/nuclear blasts).
Reservoir-induced (large dams causing crustal adjustments).
Richter Scale: magnitude = energy released.
Mercalli Scale: intensity = observed damage.
Ground shaking, land/mudslides, liquefaction, ground displacement, avalanches, dam failures, tsunamis, fires, collapse of structures.
Outermost, brittle layer.
Oceanic crust: ~5 km thick, basaltic, denser.
Continental crust: ~30–70 km, granitic, lighter.
Extends from Moho to ~2900 km.
Asthenosphere (upper mantle): partially molten, weak zone; source of magma.
Lithosphere: crust + uppermost rigid mantle (10–200 km).
Lower mantle: solid, high pressure.
Extends from 2900 km to centre (6370 km).
Composed mainly of Nickel + Iron (NiFe).
Outer core: liquid.
Inner core: solid due to immense pressure.
A vent through which lava, ash, gases are expelled.
Active, Dormant, Extinct based on periodicity.
Shield Volcanoes
Broad, gentle slopes; basaltic lava; low explosivity.
Example: Hawaiian volcanoes.
Composite Volcanoes
Alternating layers of lava + pyroclasts; highly explosive.
Calderas
Violent explosions causing collapse of summit → large depressions.
Flood Basalts
Highly fluid lava spreading over vast areas.
Example: Deccan Traps.
Mid-Ocean Ridge Volcanoes
Continuous volcanic activity along mid-oceanic ridges.
Formed when magma cools within the crust.
Batholiths
Largest intrusive bodies; exposed after denudation; granitic.
Laccoliths
Dome-shaped, flat-bottomed intrusions.
Lopoliths
Saucer-shaped intrusions.
Phacoliths
Lens-shaped intrusions in synclines/anticlines.
Sills
Horizontal intrusive sheets.
Dykes
Vertical/steep intrusions cutting across rock layers; feeders for lava flows.
The internal structure of Earth, revealed through seismic studies and indirect evidences, governs all major endogenic processes. Understanding these processes is essential to explain earthquakes, volcanism, and global tectonic phenomena that shape the Earth’s surface and influence human life.