Interior structure of the earth

Correct answer: A. There is a sudden change in state and density of the medium

At the Gutenberg boundary waves enter from solid mantle into liquid outer core causing velocity and direction change. In exams link it with shadow zones.

Correct answer: A. Liquid outer core

The wide S-wave shadow zone proves the liquid nature of the outer core. In exams connect S waves only with solid media.

Correct answer: A. Density and structural variation of the crust

Granite is lighter and basalt is denser which creates differences in the crust. In exams separate continental and oceanic crust.

Correct answer: A. Oceanic crust is repeatedly destroyed in subduction

Oceanic crust is recycled by subduction during plate movement. In exams link age difference with plate tectonics.

Correct answer: A. Liquid outer core

Movement of liquid iron nickel in the outer core is linked with the geomagnetic field. In exams connect it with the geodynamo process.

Correct answer: A. Weight of overlying materials and gravitational compression

At depth the weight of overlying layers is greater which increases pressure. In exams link pressure with state change.

Correct answer: A. Oceanic crust is mainly basaltic and keeps forming anew

Oceanic crust is thinner than continental crust mainly because it has a different composition and geological history. It is formed largely from basaltic magma at mid-oceanic ridges, where new seafloor is continuously created. Oceanic crust is generally about 5–10 km thick, whereas continental crust is much thicker and is commonly around 30–70 km thick. The repeated formation, movement and eventual subduction of oceanic crust help maintain this relatively thin layer. Its basaltic composition and its renewal at spreading ridges make option A the best available answer.

The core is not absent beneath oceans; Earth’s core lies below the mantle everywhere. Seawater cannot reduce crust to zero, and oceanic crust does not float in the atmosphere. The key comparison is between the thin, dense basaltic oceanic layer and the thicker continental layer. Strictly speaking, new formation alone is not the only explanation for its thickness, but among the given choices option A correctly identifies the important basaltic nature and continuing creation of oceanic crust. Therefore, A is acceptable.

Correct answer: A. They mostly provide information about upper parts only

Volcanic materials do not directly represent the deepest layers. In exams treat them as limited direct sources.

Correct answer: A. They reach a very small depth compared with Earth's radius

Human drilling is very small compared with Earth's total depth. In exams remember the difference between direct and indirect sources.

Correct answer: A. They indicate the composition of early solar system materials

Metallic and stony composition of meteorites indicates materials of Earth's formation. In exams treat them as indirect sources.

Correct answer: A. Most landforms and human activities occur on it

The crust is the outer solid surface where landforms and resources occur. In exams distinguish small mass from high importance.

Correct answer: A. From arrival times and velocity differences at different stations

Seismic stations record wave time and path which reveal internal boundaries. In exams remember the role of seismographs.

Correct answer: A. A zone where material properties and wave velocity change suddenly

Discontinuities help identify boundaries of layers. In exams treat Moho Gutenberg and Lehmann as key examples.

Correct answer: A. Crust and rigid part of upper mantle

The lithosphere consists of the crust and rigid upper mantle. In exams remember it as tectonic plates.

Correct answer: A. It makes mantle material less rigid and helps plate movement

Partial melting makes the asthenosphere less rigid so plates can move. In exams link it with surface plate movement.

Correct answer: A. It forms a link between surface plates and deep thermal materials

The mantle connects Earth's deep energy with surface processes. In exams treat convection as a key part of this link.

Correct answer: A. Heavy materials settling toward the center and lighter materials moving upward

Differentiation formed layers like core mantle and crust. In exams understand it through density.

Correct answer: A. Different pressure and temperature conditions

The outer core is liquid while the inner core remains solid due to extreme pressure. In exams remember both as iron nickel layers with different states.

Correct answer: A. Thickness and density

Continental crust is thicker and lighter while oceanic crust is thinner and denser. In exams remember these two properties together.

Correct answer: A. They transfer thermal energy from depth upward

Mantle convection occurs due to Earth's internal heat and affects plate movement. In exams link it with crustal processes.

Correct answer: A. They pass only through solid medium

The inability of S waves to pass through liquids helps identify the state of the outer core. This is a commonly tested clue.

Correct answer: A. Difference in density and elasticity of media

When physical properties of layers change the wave path changes. In exams consider this a method to identify internal boundaries.

Correct answer: A. Sinking of heavy elements in the early molten Earth

In the early stage heavy metals moved toward the center forming the core. In exams link it with Earth's differentiation.

Correct answer: A. They help identify state density and boundaries of layers

Different behavior of P and S waves is the basis for identifying Earth's internal layers. In exams always compare both.

Correct answer: B. When the medium is denser and more elastic

P-wave velocity is affected by the elasticity and density of the medium. In exams connect velocity changes with identification of internal layers.