Interior structure of the earth

Seismic waves give indirect information about inner layers. Exam tip: remember seismic waves as the most important indirect source.

Mining mainly gives information limited to the upper crust. Exam tip: remember the limitation of direct sources too.

Meteorites give clues about Earths formation and composition. Exam tip: keep meteorites as indirect clues.

On chemical basis the major layers are crust mantle and core. Exam tip: connect chemical division with three major layers.

Asthenosphere shows plastic and partly molten behavior. Exam tip: connect weak zone with asthenosphere.

Movement of metallic material in the liquid outer core is linked with the magnetic field. Exam tip: connect magnetic field with outer core.

Mantle convection currents help the movement of plates. Exam tip: connect convection with plate tectonics.

The mantle occupies a large part of Earths volume. Exam tip: remember mantle as the thickest major layer.

The crust is the thinnest major layer of Earth. Exam tip: remember crust as the thin outer layer.

Basalt is a dark, fine-grained volcanic rock that is especially common in oceanic crust. Oceanic crust forms mainly from magma that rises at mid-oceanic ridges, cools, and solidifies under the sea. Its composition is therefore largely basaltic. Continental crust is generally richer in lighter rocks such as granite, while the inner and outer cores are made mainly of metallic materials, not ordinary basaltic rocks.

The key comparison is between continental and oceanic crust. If a question asks for the layer dominated by basaltic rocks, choose oceanic crust because new seafloor is produced from basaltic lava. The inner core is solid and the outer core is liquid, both consisting chiefly of iron and nickel under extreme pressure and temperature. Thus option B, oceanic crust, correctly matches the rock type described.

Continental crust is linked with granitic rocks. Exam tip: connect granite with continental crust.

Change in wave velocity indicates boundary between layers. Exam tip: remember discontinuity through velocity change.

The direct answer is B: a discontinuity is a boundary where the properties of two internal layers change. In Earth science, a layer may change in composition, density, state or the speed of seismic waves. Reasoning: Earth has internal layers; the material in one layer is not always like the material in the next; the transition zone is called a discontinuity; seismic waves may change speed or direction there. A is wrong because a forest is a surface feature, not an internal boundary. B is correct. C is wrong because ocean-water colour has nothing to do with Earth’s internal layering. D is wrong because air pressure is an atmospheric idea, not the meaning of a geological discontinuity. Examples include the Moho and core-mantle boundary, but the simple exam meaning is a change boundary between layers. Memory cue: discontinuity means a break or change in continuity.

Heavier materials are more abundant toward the center so density increases. Exam tip: keep density and depth together.

From surface to center the correct order is crust mantle and core. Exam tip: identify this order in diagrams.

The core is Earth’s innermost layer and is considered its central part. It is composed mainly of iron and nickel. The mantle lies above the core, while the crust is the outermost layer. Exam tip: remember the order from outside to inside—crust, mantle, core.

Oxygen and silicon are major elements in the crust. Exam tip: remember these two first in crust composition.

The two crust types differ in thickness composition and density. Exam tip: remember the comparison of continental and oceanic crust.

Oceanic crust is found beneath the ocean floor. Exam tip: connect ocean floor with oceanic crust.

The crust is generally thicker beneath mountain regions. Exam tip: connect mountains with thicker crust.

The mantle is considered to have hot dense silicate rocks. Exam tip: connect mantle with rocky silicate layer.

The outer core consists mainly of molten iron and nickel, so it is liquid in physical state. The inner core is solid because of immense pressure, not liquid. The crust is solid, and the mantle is not completely gaseous; it is largely solid but flows very slowly over long periods. Exam tip: remember the pair outer core—liquid and inner core—solid.

Density helps understand distribution of materials inside Earth. Exam tip: connect heavy materials with deep layers.

The outermost major part is crust and the innermost part is core. Exam tip: remember outermost crust and innermost core directly.

Heavy materials moved toward the center because of higher density. Exam tip: connect iron nickel core with density differentiation.