The Structure of the Earth — UPSC Essential Understanding Earth’s internal structure helps explain earthquakes, volcanoes, plate tectonics, and magnetic fields. The Earth is divided into three major layers (Crust, Mantle, Core) and several sub-layers crucial for GS-1. ⸻ 1. Crust • Thickness: 5–8 km under oceans; up to 30–32 km under continents • Composition: Granitic rocks (continental crust), basaltic rocks (oceanic crust) • Key Fact: Makes up just 1% of Earth’s volume • Boundary: Moho (Mohorovičić Discontinuity) ⸻ 2. Mantle • Extends to 2,900 km depth • Composition: Ultramafic silicates (rich in Mg & Fe) • Accounts for 84% of Earth’s volume Sub-layers: • Lithosphere: Rigid crust + uppermost mantle (~100 km). Broken into tectonic plates • Asthenosphere: Partially molten, plastic layer (~100–700 km); allows plate movement • Lower Mantle: More rigid due to immense pressure ⸻ 3. Core • Extends from 2,900 km to the centre at 6,371 km • Composition: Mostly iron, nickel (NiFe) Sub-layers: • Outer Core: Liquid; responsible for Earth’s magnetic field • Inner Core: Solid due to extreme pressure • Boundary: Lehmann Discontinuity (between inner & outer core)