Geology and Earth Structure

Planetary differentiation is the process by which a planet separates into layers of different composition and density. During Earth's early molten state, heavier elements (iron, nickel) sank to form the core, while lighter materials (silicates) rose to form the mantle and crust. This created the layered interior structure we observe today.

The lithosphere is the rigid outer layer of Earth, consisting of the crust and uppermost mantle. It's broken into tectonic plates. The term 'lithosphere' literally means 'rocky sphere' and encompasses all solid rock above the asthenosphere. While the crust is part of it, the lithosphere is the complete rigid outer shell.

The Mohorovicic discontinuity (Moho) is the boundary between Earth's crust and the mantle. It was discovered by Andrija Mohorovicic in 1909 when he observed seismic wave velocity changes at this boundary. The Moho varies in depth - about 5-10 km under oceans and 30-50 km under continents. The Gutenberg discontinuity marks the core-mantle boundary instead.

The clue for first blank is found in 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 it as we would have thought. As 'built' is one of our options, hence (4) is the answer.

Japan experiences the most frequent earthquakes because it sits on multiple tectonic plate boundaries (Pacific, Philippine Sea, Eurasian, and North American plates). About 20% of the world's earthquakes of magnitude 6.0 or greater occur in Japan, making it the most seismically active country among the options.

Flood basalt province, this type of volcano pour out fluid lava that flows for large distance.

The Richter scale, developed by Charles Richter in 1935, is the most well-known magnitude scale for measuring earthquake strength based on seismic wave amplitude. The Mercalli scale measures intensity (observed damage/effects), not magnitude. Kite and Avalanche scales are not relevant to seismology.

Abyssal plains are extensive, flat regions of the ocean floor that lie between continental margins and mid-ocean ridges. They are among the flattest features on Earth, formed by the deposition of sediments over millions of years. Ridge plain is not a standard geographical term, while continental plain and 'Reep plain' are incorrect in this context.

S -waves or secondary waves which only passes through the solid forms

Wegener proposed two main forces to explain continental drift: pole-fleeing force (centrifugal force due to Earth's rotation) and tidal force (gravitational pull of the moon and sun). While his theory was incomplete, these were the mechanisms he suggested. Gravitational force, solar energy, and wind energy are not the specific forces Wegener identified.

McKenzie, Parker, and Morgan were all key advocates and developers of the plate tectonics theory in the 1960s. McKenzie and Parker worked on plate kinematics, while Morgan proposed the concept of mantle plumes and hotspots. All three made fundamental contributions to establishing plate tectonics as the unifying theory of geology.

The lithosphere consists of the crust and the uppermost solid part of the mantle. It is the rigid outer layer of Earth that is broken into tectonic plates. Options A, B, and C are incorrect because the core is not part of the lithosphere, and 'upper core' is not a standard geological term.

divergent boundary, American plates are separated from the Eurasian and African plates

Among the options, the Indo-Australian plate (including New Zealand) is the major plate, though typically referred to as the Indo-Australian Plate. Philippine, Arabian, and Cocos plates are all minor or secondary plates. The seven major plates are: Eurasian, Pacific, Indo-Australian, African, North American, South American, and Antarctic.

In convergent boundaries, the subduction zone is where one tectonic plate descends beneath another into the mantle. This process creates deep ocean trenches, volcanic arcs, and earthquakes. 'Convergent zone' is too general, while 'deduction zone' and 'original site' are not geological terms.