Sources of information

Lava comes from inside but its source region may be limited. Exam tip: write limitation of volcanic source.

Sharp velocity change indicates different material or state. Exam tip: connect it with discontinuity.

Direct answer: A, the region has at least solid properties. S waves are shear seismic waves. A shear wave needs a material that can resist a sideways change in shape, which is a solid property. Therefore, if S waves reach a region, it is reasonable to infer that the region behaves as solid, at least along the relevant path and under those conditions. Option A is correctly cautious: it does not claim more than the evidence proves. Option B, definitely liquid, is the opposite of what S-wave transmission suggests; S waves do not pass through a completely liquid medium. Option C, only air, is impossible for this seismic inference. Option D, weather region, belongs to atmospheric study and has no connection with seismic wave type. Memory cue: P waves pass through solids and liquids; S waves require solidity.

Rock samples and seismic evidence answer different questions about Earth’s interior. A sample can be examined directly, so it may reveal the minerals, texture, and composition of the material from which it came. However, samples usually come from accessible or limited locations and cannot directly show the deep interior. Seismic evidence therefore adds information that cannot be obtained by ordinary sampling.

Earthquake waves travel through the planet and change speed or direction when they meet materials with different properties. These changes help scientists infer boundaries and deeper layers. Thus, samples provide direct but limited evidence, while seismic waves provide indirect evidence about great depths. Combining both gives a stronger and more balanced understanding. Therefore, option A is correct; the other choices confuse this scientific method with unrelated activities.

Magnetic field indicates metallic nature but S wave evidence suits liquid state better. Exam tip: separate roles of evidences.

Gravity can indicate density and magnetism can indicate metallic material. Exam tip: write multi-source analysis.

The direct answer is A: use meteorites for comparison with early Solar System materials. Meteorites are natural objects that formed from or preserve very old Solar System material. Since Earth’s deep interior cannot be sampled directly, scientists compare the composition of meteorites with models of the material from which the planets formed. This comparison helps them reason about Earth’s bulk composition and early development, but it is indirect evidence. Option A is correct. Option B is wrong because no meteorite is a sample brought up from Earth’s centre. Option C is wrong because a seismograph record measures seismic waves. Option D is wrong because a rain gauge measures rainfall. Memory cue: meteorites are comparative clues, not core samples.

Direct answer: A, changes in internal media and the nature of the core. Seismic waves do not travel in a perfectly straight, unchanged way through Earth. Refraction means a wave bends when its speed changes between materials. A shadow zone is an area where a particular wave is weak or absent because its path is bent, blocked or affected by a boundary. Together, these observations reveal boundaries and changes inside Earth, including information about the core. Option A is correct. Option B, rainfall distribution, concerns climate and has no role in explaining seismic paths. Option C, surface soil alone, cannot explain deep refraction and shadow zones. Option D, population density, is unrelated to wave propagation. Exam cue: unusual wave paths are evidence about hidden internal layers.

Direct sources are not enough for deep parts. Exam tip: understand roles of both sources separately.

Bending of P wave may indicate medium change. Exam tip: connect refraction with internal boundary.

A rock sample is a piece of actual material collected from the Earth, so it provides direct physical evidence about the composition and properties of a rock or layer. A gravity anomaly is different: it is a measured difference between observed gravitational force and the value expected for a particular area. This difference can suggest variations in underground density, but it does not itself provide a piece of rock for direct inspection.

Option A is correct because it clearly distinguishes direct material from an indirect clue. Gravity data help scientists infer hidden structures, such as denser or less dense masses below the surface, while a rock sample can be examined directly in a laboratory. The other choices incorrectly connect these geological sources with weather or population, or wrongly call a gravity anomaly a direct rock sample.

Direct answer: A, compare other evidence and make a cautious conclusion. Earth’s interior cannot usually be observed directly, so scientists use indirect clues such as seismic waves, gravity, magnetism and rocks. If two clues differ, the correct scientific response is not to choose one blindly. First check the reliability and limits of each source, then compare them with additional evidence, and finally state a conclusion with suitable caution. Option A follows this process. Option B is unsafe because one unchecked clue may be incomplete or misleading. Option C incorrectly changes geological evidence into weather evidence. Option D wrongly dismisses a relevant question. A careful conclusion is not weakness; it is honest reasoning based on evidence. Memory cue: different clues require comparison, checking and cautious inference.

Mine temperature is useful but does not tell full internal heat. Exam tip: also remember geothermal gradient and radioactive heat.

Ocean floor rocks are related to oceanic crust. Exam tip: identifying scope of source is necessary.

No single source is complete in internal study. Exam tip: write combined evidence and limitation.

Wave velocity and density clues relate to nature of medium. Exam tip: use possible conclusion carefully.

Volcanic material gives internal clue but not direct evidence of the core. Exam tip: write limitation of source.

Rock analysis gives chemical information of real material. Exam tip: remember sample source for composition.

S waves are transverse (shear) waves and cannot travel through a liquid medium. Since Earth’s outer core is liquid, S waves are blocked by it, producing an S-wave shadow zone. In contrast, P waves are generated by earthquakes, not by rainfall. Exam tip: remember that P waves travel through solids, liquids and gases, whereas S waves travel only through solids.

Direct sources are limited in deep interior so indirect sources are necessary. Exam tip: write both use and limitation.

A seismic layer boundary is more convincing when several independent observations point to the same depth. A sudden change in wave velocity may show that the material has different properties. A change in direction indicates refraction at an interface, while reflected waves show that part of the energy has bounced back from that interface. When these clues occur together, the interpretation of a boundary is stronger than when it depends on only one observation. Scientists still compare readings from many stations and wave types.

Option A is therefore the strongest choice: it combines velocity change, direction change, and reflection. River names, rainfall averages, and crop reports do not record the behaviour of seismic waves and cannot identify an underground seismic boundary. The question asks for a combined seismic clue, so the three related observations fit precisely. The supplied answer is consistent with the basic method used to infer internal layers, even though real analysis can involve additional evidence.

Balanced conclusion is made by combining many evidences. Exam tip: treat combined analysis as scientific method.

Deep parts are difficult to reach so seismic gravity and magnetic evidence are important. Exam tip: write problem and solution together.

Magnetic clue suggests metallic material and S wave arrival shows solid properties. Exam tip: keep roles of different evidences separate.

Crustal samples show limited depth and seismic clues inform deeper layers. Exam tip: draw conclusions according to source scope.