Geology and Earth Structure

This is the correct statement. The crust is neither produced nor destroyed as the plates slide horizontally past each other at the transform faults. Transform faults are the planes of separation generally perpendicular to the mid oceanic ridges.

This is the correct answer, as both the statements 'a' and 'b' are correct.

The circum-Pacific belt (Ring of Fire) is prone to earthquakes due to young folded mountains (statement 1), active volcanoes (statement 2), and convergent plate boundaries (statement 4). It is NOT primarily a zone of divergent boundaries (statement 3 is false), making option B (1, 2, and 4) correct.

The Mohorovicic discontinuity (Moho) is the boundary between Earth's crust and the mantle. It occurs at varying depths - 5-10 km beneath oceans and 30-50 km beneath continents. At this boundary, seismic wave velocities change abruptly due to differences in composition and density between crustal and mantle rocks.

Monoclines are folds where strata are horizontal on both sides but dipped at a single step - essentially creating locally inclined beds. They result from vertical displacement or differential compaction, not from faulting, inversion, or distortion of the entire bed sequence. The beds maintain their horizontal attitude except at the flexure point where they become inclined.

Primary waves (P-waves) are longitudinal, compressional seismic waves that push and pull rock in the direction of wave propagation, similar to how sound waves move through air. They are the fastest seismic waves and travel through both solids and liquids, though faster through solids due to higher elasticity. All three statements (A, B, C) are correct.

The Karroo (or Karoo) in South Africa refers to the step-like landscape features - the Great Escarpment that forms steps from coastal lowlands up to the high plateau interior. These are erosional features rather than rift valleys (A) or dome structures (B). The Karoo is famous for these stepped plateau edges and its extensive sedimentary rock layers.

P-waves (primary) arrive first at seismic stations (statement 1 correct). S-waves (shear) travel through solids but NOT liquids (statement 2 wrong). The time difference between P and S arrivals is used to triangulate epicenter location (statement 3 correct). Richter scale is logarithmic (statement 4 correct). Therefore statements 1, 3, and 4 are correct (option B).

Mid-ocean ridges form at divergent plate boundaries where tectonic plates move apart, allowing magma to rise and create new oceanic crust. This process, called seafloor spreading, creates the characteristic ridge system. Convergent plates create trenches/mountains (B), transform faults create lateral movement (C), and parallel movement is not a standard plate boundary type.

The clue for the first blank is found in the latter part of the sentence as this is an explanation to the first part. “Pushed up” and “accumulated a mass” signifies that a volcano built a mountain, and not collapsed, as we would have thought. As ‘built’ is one of our options, hence, (4) is the answer. ‘Forged’ in option (5) is to form or shape (metal) with blows or pressure from a hammer, press, or other machine, usually after heating; which is not coherent with volcanoes building up a mountain.

The lithosphere is Earth's rigid outer shell, comprising the crust and uppermost solid mantle. It ranges from 50-100 km in thickness and is broken into tectonic plates that move over the more ductile asthenosphere below. This rocky shell provides the solid ground on which we live and the foundation for all landforms and geological activity.

The asthenosphere is the ductile, highly viscous layer of the upper mantle on which the lithospheric plates float. It extends from about 100-330 km depth. Its plasticity allows tectonic plates to move. The mesosphere is the lower mantle, barysphere is another term for the Earth's core, and these terms help us understand Earth's internal structure.