JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II GENERAL GEOLOGY Previous Question Paper (March - 2021 - R18)

The origin of the Earth is explained by several key hypotheses:

• Nebular Hypothesis: Proposed by Kant and Laplace, it suggests the solar system formed from a rotating cloud of interstellar gas and dust. As the nebula cooled and contracted, it spun faster, shedding rings of material that condensed into planets.
• Planetesimal Hypothesis: Chamberlin and Moulton proposed that a passing star exerted gravitational forces on the Sun, pulling out filaments of gaseous matter. These filaments cooled into solid bodies called planetesimals, which eventually accreted to form planets.
• Tidal Hypothesis: Jeans and Jeffreys suggested that a large star passed close to the Sun, creating a tidal bulge of solar material. This material was torn away and broke into segments that condensed into the planets.
• Protoplanet Hypothesis: The modern accepted theory, which refines the nebular model, stating that the solar system formed from a dense cloud of gas and dust. Gravitational collapse led to a central protosun surrounded by a rotating disk, where dust grains collided and clumped together to form protoplanets.

The theory of Plate Tectonics states that the Earth's rigid outer shell, the lithosphere, is broken into several large and small segments called tectonic plates. These plates float on the semi-fluid, plastic-like asthenosphere below.

Key aspects of the theory include:

• Driving Mechanism: Convection currents within the Earth's mantle are the primary drivers of plate movement. Heat from the core causes mantle material to rise, spread, cool, and sink, dragging the overlying plates with it.
• Plate Boundaries: Interactions occur primarily at three types of boundaries:
  • Divergent: Plates move apart, creating new crust (e.g., Mid-Atlantic Ridge).
  • Convergent: Plates collide, leading to subduction (where one plate sinks beneath another) or mountain building (e.g., Himalayas).
  • Transform: Plates slide horizontally past each other, causing significant seismic activity without creating or destroying crust (e.g., San Andreas Fault).
• Geological Significance: This theory explains the distribution of earthquakes, volcanic activity, mountain ranges, and the formation of ocean basins, providing a unified framework for understanding global geological processes.