Interior structure of the earth

Sial is rich in silica and aluminium and relates to continental crust. Exam tip: remember Sial as Si plus Al.

Sima is considered rich in silica and magnesium and is linked with oceanic crust. Exam tip: remember Sima as Si plus Mg.

The mantle is believed to be made of hot dense silicate rocks. Exam tip: connect mantle with silicate rocks.

Based on chemical composition, Earth is divided into crust, mantle and core. Exam tip: remember this three-layer division.

The lithosphere is the upper rigid part of Earth. Exam tip: remember lithosphere in physical property based division.

Asthenosphere material is considered semi-fluid and plastic. Exam tip: link convection and plate motion with it.

Direct answer: Option D is correct. Earth has an outer core between the mantle and the inner core. It is made mainly of metallic material, especially iron and nickel, and the extremely high temperature keeps it in a liquid state. Movement of this liquid metal is associated with Earth’s magnetic field. A is wrong because granite is a light rock found mainly in continental crust, not the outer core. B is wrong because the crust is Earth’s outermost solid layer; the outer core is deep inside. C is wrong because the atmosphere is the gaseous envelope surrounding Earth, far above the crust. D correctly identifies both the important state, liquid, and composition, metallic material. Memory cue: outer core means liquid metal; inner core means solid metal.

The inner core is Earths solid metallic center. Exam tip: connect solid center with inner core.

Changes in seismic wave velocity indicate changes in internal layers. Exam tip: link velocity change with discontinuities.

Direct information is mainly limited to the upper crust. Exam tip: remember indirect evidence for deeper parts.

The core has very high density because it contains heavy metals. Exam tip: connect iron and nickel with high density.

Direct answer: Option C is correct. The crust is Earth’s thin, solid outer layer. Below it lies the much thicker mantle, and still deeper are the outer and inner core. The crust may be about 5–10 km thick under oceans and roughly 30–70 km under continents, so it is thin compared with the mantle and core. A is wrong because the mantle is a very thick layer. B is wrong because the core includes enormous inner and outer regions and is not the thinnest major layer. D is wrong because the outer core is only one part of the core and is much thicker than the crust. C works because “crust” means Earth’s thin outer skin. Exam cue: outermost and thinnest major layer usually points to crust.

Meteorite composition gives clues about Earths formation. Exam tip: keep meteorites under indirect evidence.

The lithosphere is made of the crust and rigid upper mantle. Exam tip: it is basic for plate boundary concepts.

Answer: D, the Moho discontinuity. The Moho, or Mohorovičić discontinuity, is the boundary between Earth’s crust and the mantle. Seismic waves change velocity noticeably as they pass from crustal material into mantle material because the composition and physical properties of the rocks change. Option A, the Gutenberg discontinuity, is associated with the boundary between the mantle and the outer core. Option B, the Lehmann discontinuity, refers to the boundary between the outer core and inner core. Option C, the Repetti discontinuity, is a boundary within the mantle, not the crust–mantle boundary. Therefore only option D fits both the location and the seismic-wave clue. Memory cue: Moho means mantle begins below the crust; Gutenberg is mantle–outer core, and Lehmann is outer–inner core.

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

Mantle convection currents help in plate movement. Exam tip: link convection with plate tectonics.

Oxygen and silicon are among the major elements in the crust. Exam tip: remember oxygen and silicon in crust composition.

A discontinuity is a boundary where wave velocity or properties change suddenly. Exam tip: understand discontinuity as a layer boundary.

Oceanic crust is denser due to its basaltic composition. Exam tip: remember basalt equals dense.

The correct answer is B: crust, mantle, outer core, and inner core. To understand the order, imagine moving downward from Earth’s surface. First we meet the crust, the thin, solid rocky outer shell. Below it is the mantle, a much thicker layer of hot rock. Deeper still is the core, which has a liquid outer core and a solid inner core. Thus the order from outside toward the centre is crust → mantle → outer core → inner core. A is wrong because it places the mantle before the crust. C is wrong because it puts the outer core above the mantle. D gives the layers in the reverse direction, from the centre outward. Memory cue: “Crust, Mantle, Outer core, Inner core”—the first letters form CMOI.

S waves do not pass through the liquid outer core. Exam tip: connect S wave shadow zone with outer core.

Gravity and magnetic measurements provide indirect information about Earths interior. Exam tip: keep geophysical methods under indirect sources.

From top to bottom, the correct order is crust, mantle and core. Exam tip: identify this order first in diagrams.

The speed and direction of seismic waves give information about Earths inner layers. Exam tip: treat seismic evidence as the most important indirect source.