Interior structure of the earth

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.

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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