Interior structure of the earth

The Moho discontinuity marks the boundary between the crust and mantle. For exams remember it with a sudden rise in seismic wave velocity.

Oceanic crust is mainly basaltic in composition so it is denser. In exams connect it with plate formation at ridges.

Deep crustal roots form below mountains which increases thickness. For exams understand it through the Himalayas.

The lithosphere is rigid while the asthenosphere is relatively weak and partly molten. In exams treat it as the base of plate movement.

The Lehmann discontinuity marks the boundary between the outer and inner core. For exams remember it through change in P-wave velocity.

S waves do not travel through liquids so their absence in the outer core proves its liquid state. In exams treat it as a key clue.

Pressure in the inner core is so high that iron and nickel remain solid. For exams remember the balance of temperature and pressure.

Greater depth has higher pressure and more heavy elements which increase density. In exams link density with internal differentiation.

Sial contains silica and alumina rich material and is linked with continental crust. In exams treat Sial as a lighter layer.

Sima has more silica and magnesium and is linked with oceanic crust. In exams consider it denser than Sial.

The mantle extends to about 2900 km so it forms a large part of Earth's volume. In exams distinguish thickness from volume.

The weak nature of the asthenosphere helps plate movement. In exams connect it with convection currents.

The mantle is solid but can deform plastically over long time. In exams do not treat solid and rigid as identical.

Changes in P-wave velocity show boundaries and material properties of internal layers. In exams identify discontinuities through this.

The Conrad discontinuity is associated with velocity change within continental crust. In exams distinguish it from the Moho.

Seismic waves show different velocity and direction in different materials. In exams treat reflection and refraction as clues.

Layers are mainly identified through seismic waves and material properties. In exams do not treat direct drilling as sufficient evidence.

Earth's average density is higher than surface rocks and meteorites indicate metallic material. In exams this is indirect evidence.

Decay of elements like uranium and thorium gives internal heat. For exams remember it along with residual heat of planet formation.

Geothermal gradient indicates increase of temperature with depth. In exams keep local variation in mind.

At the Moho material composition changes and wave velocity rises. In exams treat it as evidence of layer change.

The mantle has heavier silicate minerals so it is denser than the crust. In exams link composition with density.

Mechanical classification is based on material behavior such as rigid lithosphere and weak asthenosphere. In exams keep it separate from chemical classification.

In chemical classification the crust mantle and core differ in composition. For exams connect it with material makeup.

High average density shows heavy materials like iron and nickel inside. In exams treat it as a clue to core composition.