Interior structure of the earth

P-waves are compressional and S-waves cannot pass through liquids. Exam tip: use this difference to understand outer core.

Stopping of S-waves in outer core is evidence of its liquid state. Exam tip: apply wave properties even in hypothetical questions.

Sial is linked with lighter continental and sima with denser oceanic nature. Exam tip: use them carefully with modern terms.

Internal heat drives slow movement of mantle material. Exam tip: connect mantle convection with plate movement.

Rate of temperature increase changes with place and depth. Exam tip: do not treat geothermal gradient as simply linear.

Very high pressure can prevent melting. Exam tip: always mention pressure while explaining inner core state.

Low velocity may indicate weak or partly molten zone. Exam tip: connect low velocity zone with asthenosphere.

Mantle is a very large part of Earth and affects plates by convection. Exam tip: treat mantle as an active internal layer.

D double prime is considered at the base of lower mantle. Exam tip: understand it as a special deep mantle layer.

The direct answer is option C, the large mass and state of the core. Density tells us how much mass is packed into a unit volume, while pressure tells us how strongly material is compressed. Earth’s core contains very dense metallic material, mainly iron and nickel, and experiences enormous pressure. Therefore pressure and density together help scientists understand why the core has a very large mass and why its inner and outer parts have different physical states. Option A, rainfall, depends mainly on atmosphere and water cycle, not core pressure and density. Option B, river bends, depends on slope, speed, erosion and deposition. Option C is correct. Option D, soil moisture, is controlled mainly by rainfall, soil and evaporation. Exam cue: core questions connect density with deep metallic matter and pressure with compression and state.

Oceanic crust keeps forming and getting destroyed in subduction. Exam tip: connect it with plate tectonics.

Crust and lithosphere describe Earth in different ways. The crust is the outer chemical layer, classified mainly by its composition as continental or oceanic crust. The lithosphere is a mechanical layer: it includes the crust plus the strong, rigid uppermost part of the mantle. It forms hard tectonic plates that move over the softer, weaker asthenosphere. Therefore, the two terms overlap but are not identical.

Option A is correct because it includes both the crust and the rigid upper mantle in the lithosphere. The other choices are plainly incorrect: these structures are not parts of the atmosphere, the crust is not inside the core, and the lithosphere is not made only of water. Remembering the different bases of classification prevents confusion between a chemical layer and a mechanically strong layer.

Chemical basis considers composition and mechanical basis considers rigidity or ductility. Exam tip: remember both lists separately.

Shadow zone forms by refraction and blockage of waves. Exam tip: view it as evidence of spherical layers.

Discontinuities occur because material properties change. Exam tip: write wave velocity change as evidence of layering.

There is sharp change in material properties at core-mantle boundary. Exam tip: connect it with deep internal processes.

Magnetic and gravity studies give clues about internal materials. Exam tip: write them as indirect geophysical sources.

The direct answer is C: the Moho is a clear seismic boundary between the crust and the mantle. Moho is short for Mohorovičić discontinuity. A discontinuity is a zone where the properties of Earth material change noticeably. At the Moho, seismic-wave velocity changes because the composition and density of the material below the crust differ from those in the crust. The reasoning is: observe earthquake waves; notice a sudden change in their speed or path; identify this boundary; infer that the mantle begins below it. Option C is correct. Option A is wrong because Moho is not a geographical edge of a river valley. Option B is wrong because it has no connection with monsoon limits. Option D is wrong because the outer core lies much deeper, below the mantle, and is not the surface marked by Moho. The depth of Moho varies under continents and oceans, but its meaning remains the crust–mantle boundary. Memory cue: “Moho means mantle starts below crust.”

Meteorites provide indirect comparison not direct Earth samples. Exam tip: write both their use and limitation.

Geomagnetic variation is linked with moving metallic liquid in outer core. Exam tip: connect magnetism with core activity.

Continental crust is thick and light granitic. Exam tip: check both thickness and density clues.

The direct answer is C: melting point may generally increase when pressure increases. Pressure pushes particles closer and can favour the solid state, so more heat may be needed to melt a material. The careful word is “generally” or “may,” because the exact effect depends on the substance and its phase relation; the school-level Earth-science conclusion is that high pressure can raise the melting point. A is wrong because pressure does not make every melting point zero. B is wrong because pressure does have a relationship with melting behaviour. D is wrong because rainfall is an atmospheric process and does not control the melting point of deep minerals. C is therefore the best option and helps explain why the inner core can remain solid despite very high temperature. Memory cue: high pressure favours solidity, but remember exceptions exist.

Pressure along with temperature determines material state. Exam tip: do not decide state by temperature alone.

Seismic waves do not give direct samples but reveal internal structure. Exam tip: treat seismology as the main indirect tool.

Chemical division has crust mantle and core as main parts. Exam tip: do not mix them with mechanical names.