Interior structure of the earth

The governing concept is the compositional structure of Earth’s interior. The core is traditionally described as being rich mainly in nickel and iron, represented by the term ‘nife’ from nickel and ferrum, the Latin word for iron. Therefore, option C is correct. The mantle is dominated by silicate minerals, the crust is the thin outer rocky layer, and the lithosphere includes the crust plus the rigid uppermost mantle; none of these is the mainly nickel–iron layer.

The crust is the outermost and thinnest solid layer of Earth. Exam tip: remember it as the upper hard layer.

The mantle lies directly beneath the crust and is the thickest major layer of Earth’s interior. The outer core and inner core lie below the mantle, so they are not correct. Exam tip: remember the main sequence as crust, mantle, core.

The core is the deepest layer located at the center of Earth. Exam tip: connect core with the center.

The core is believed to be mainly made of iron and nickel. Exam tip: connect nife with nickel and ferrum.

The direct answer is B: granite is mainly associated with the continental crust. To understand this, the Earth’s crust is not identical everywhere. Continental crust is generally thicker, less dense and commonly made of granitic rocks, while oceanic crust is thinner, denser and commonly basaltic. In school geography, continental crust is also remembered as sial, meaning it is rich in silica and aluminium. Step by step: identify the question as asking about continental, not oceanic, crust; connect continental crust with granite and sial; then select B. Option A, basalt, is mainly associated with oceanic crust, so it is less correct here. Option B is correct because granite is the standard textbook material linked with continental crust. Option C, iron, is important in the deeper metallic core and is not the main material of continental crust. Option D, nickel, is also associated mainly with the core, not the crust. The distinction is a broad school-level generalisation, because crust contains several minerals, but among these options granite is clearly best. Memory cue: continental crust equals granite and sial; oceanic crust equals basalt and sima.

Oceanic crust is mainly composed of basalt, a dark, dense volcanic igneous rock rich in iron and magnesium. It forms when magma rises at mid-ocean ridges, cools and solidifies, and it is continuously renewed as new seafloor develops. By contrast, continental crust contains more granitic rocks and is generally less dense. Limestone is a sedimentary rock formed largely from deposited carbonate material, while marble is a metamorphic rock produced when limestone is altered by heat and pressure. Therefore option C is correct. The older school term “sima” also reflects the silica- and magnesium-rich character traditionally associated with oceanic crust.

The direct answer is A: the crust and the rigid part of the upper mantle. The lithosphere is Earth’s hard, outer layer. It includes the crust, which is the thin rocky surface on which continents and ocean floors rest, and the uppermost mantle that is sufficiently rigid to behave as solid rock. The lithosphere is broken into tectonic plates that move slowly over the softer asthenosphere below. Option A is correct because it gives both main components. Option B, only the outer core, is wrong because the outer core lies much deeper and is liquid metal, not part of the lithosphere. Option C, only oceans, is wrong because oceans are water; oceanic crust is part of the lithosphere, but the whole lithosphere is not only oceans. Option D, only atmosphere, is wrong because the atmosphere is the gaseous envelope around Earth. Reasoning: crust + rigid uppermost mantle = lithosphere. Memory cue: lithosphere means the hard rocky shell, not the liquid core, air or water alone.

The asthenosphere is a plastic zone of the upper mantle. Exam tip: link plate movement with this zone.

The Moho discontinuity is the boundary between crust and mantle. Exam tip: connect Moho with the base of the crust.

Lehmann discontinuity is linked with the boundary between outer and inner core. Exam tip: remember it as the inner core boundary.

The direct answer is D, liquid. Earth’s outer core is believed to be a very hot, fluid layer made mainly of iron and nickel. Scientists infer this from earthquake-wave behaviour: S waves cannot travel through liquids, and they do not pass through the outer core. P waves can travel through it but change speed and direction. The outer core is different from the inner core, which is solid because of enormous pressure despite its high temperature. Option A, solid, describes the inner core more accurately, not the outer core. Option B, gaseous, is wrong because the core is compressed metal, not gas. Option C, plasma, is not the school-level physical state used for the outer core; it is not described as a freely ionized gas layer in this context. Option D is correct because seismic evidence supports a liquid outer core. Reasoning: S-wave shadow zone and P-wave changes → outer core is fluid. Memory cue: outer core flows; inner core is firm.

The inner core is considered solid due to very high pressure. Exam tip: link high pressure with solid inner core.

Seismic waves give information about Earths interior. Exam tip: distinguish direct and indirect sources.

The mantle is the thickest major layer of Earth. Exam tip: connect mantle with most of Earths volume.

Continental crust is generally thicker and relatively lighter. Exam tip: remember continental crust as granitic and light.

Oceanic crust is the thinner and denser of the two main kinds of Earth’s crust. It lies beneath the oceans and is usually made largely of dark, iron- and magnesium-rich basaltic rocks. Continental crust is generally thicker and less dense, and it contains more silica-rich rocks such as granite. Because oceanic crust has greater density, it tends to lie at a lower level than continental crust, helping to form ocean basins. The words “thin” and “dense” are therefore the key features to remember.

Choice B is correct because it states both of these general properties: oceanic crust is thinner and denser than continental crust. Choice A reverses both comparisons. Choice C is incorrect because the crust is solid rock, not gas. Choice D is also incorrect because oceanic crust is not only granitic; basalt is its characteristic rock type, whereas granite is more typical of continental crust. These are general comparisons, not absolute claims for every small region.

Temperature generally increases with depth. Exam tip: remember the basic idea of geothermal gradient.

Pressure increases with depth due to the weight of overlying layers. Exam tip: link solid inner core with high pressure.

The direct answer is D, S wave. Earthquake waves are vibrations released by an earthquake. P waves are compressional waves and can travel through solids, liquids and gases. S waves are shear waves: they make particles move perpendicular to the direction of travel, so the material must provide resistance to shearing. Liquids cannot support this kind of shear motion, so S waves cannot pass through them. Option A, P wave, is wrong because P waves can pass through liquids, although their speed changes. Option B, surface wave, is wrong because it is a wave that travels along the surface and is not the specific body wave identified by this property. Option C, sea wave, is an ordinary water wave, not the earthquake-wave answer asked here. Option D is correct. This fact also helps prove that Earth’s outer core is liquid: S waves disappear at the outer core. Memory cue: S means shear; no shear in liquid.

P waves can pass through both solids and liquids. Exam tip: remember P as primary and faster wave.

Mining gives direct information about upper layers of Earth. Exam tip: keep mining and volcanic materials under direct sources.

Lava gives samples of internal materials. Exam tip: remember volcanic material as direct evidence.

The crust is thicker beneath continents than beneath oceans. Exam tip: remember continent equals thicker crust.

Lithospheric plates move over the asthenosphere. Exam tip: connect plate movement with asthenosphere.