Dibrugarh University B.Sc. Geology Major 2025 Question Paper (PYQ) with Answers 1st Semester

Question 1. Fill in the blanks:

(a) The heliocentric model was proposed by _________.

Ans: The heliocentric model was proposed by Nicolaus Copernicus.

(b) ________ is regarded as the father of modern astronomy.

Ans: Galileo Galilei (or Nicolaus Copernicus) is regarded as the father of modern astronomy.

(c) The largest meteorite ever found on the earth is the _________.

Ans: The largest meteorite ever found on the earth is the Hoba meteorite.

(d) The earth formed over 4.6 billion years ago out of a mixture of ________ and ________.

Ans: The earth formed over 4.6 billion years ago out of a mixture of dust and gas.

(e) The Himalayan Mountain range began forming during the ________ Era.

Ans: The Himalayan Mountain range began forming during the Cenozoic Era.

Question 2. Describe about the nebular hypothesis and its drawbacks.

Ans: The Nebular Hypothesis

The Nebular Hypothesis, initially proposed by Immanuel Kant (1755) and mathematically formulated by Pierre-Simon Laplace (1796), is a widely accepted model explaining the formation of the solar system.

Process:

The solar system began as a giant, rotating cloud of interstellar gas and dust called the solar nebula.

Due to a disruptive event (like a nearby supernova) or gravitational instability, the nebula began to collapse under its own gravity.

As it collapsed, the conservation of angular momentum caused the nebula to spin faster, flattening it into a protoplanetary disk.

The majority of the mass concentrated in the center, heating up to form the proto-Sun.

In the cooler outer regions of the disk, matter collided and accreted to form planetesimals, which eventually aggregated into the planets.

Drawbacks of the Classical Nebular Hypothesis

Despite its strengths, the original Kant-Laplace hypothesis faced significant criticisms, leading to modern modifications:

Angular Momentum Distribution: The most critical drawback is the distribution of angular momentum. The Sun contains about 99.8% of the solar system's mass but possesses only about 2% of its angular momentum. The planets, comprising merely 0.2% of the mass, hold 98% of the angular momentum. The classical hypothesis could not explain how the central proto-Sun transferred its angular momentum to the outer planets.

Formation of Rings vs. Planets: Laplace suggested that the shrinking nebula left behind discrete rings of matter that condensed into planets. However, physicists like James Clerk Maxwell demonstrated that a ring of gaseous material would not condense into a single planet due to gravitational dispersion forces; instead, it would remain as a ring of small particles.

Note: Modern variations of this theory involve magnetic braking and solar wind to explain the angular momentum transfer.

Question 3. Write short notes on any two of the following:

Note: Solutions for all three options are provided below for comprehensive study.

(a) Iron meteorite

Ans: Iron meteorites are a major class of meteorites composed overwhelmingly of an iron-nickel alloy, primarily the minerals kamacite and taenite.

Origin: They are believed to be the fragmented cores of larger, ancient asteroids that underwent planetary differentiation (melting and separation into a metallic core and a rocky mantle) before being destroyed by collisions.

Characteristics: They have an extremely high density. When cut, polished, and etched with weak acid, most iron meteorites display a distinct, intersecting crystalline structure known as the Widmanstätten pattern, which indicates an extremely slow cooling rate over millions of years within the parent body's core.

Significance: They provide direct analogues for the composition of Earth's own metallic core. The Hoba meteorite in Namibia is the largest known example on Earth.

(b) Geological timescale

Ans: The Geological Timescale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.

Hierarchy: The GTS is broken down into a hierarchical sequence of time units. In descending order of duration, these are: Eons, Eras, Periods, Epochs, and Ages.

Basis: The divisions are primarily based on major geological and evolutionary events recorded in the rock and fossil records, such as mass extinctions (e.g., the Permian-Triassic extinction boundary) or the sudden appearance of new life forms.

Modern Calibration: While historically based on relative dating principles (Steno's Laws, Faunal Succession), the modern GTS is continuously refined with absolute ages using radiometric dating (chronostratigraphy) coordinated by the International Commission on Stratigraphy (ICS).

(c) Types of asteroid

Ans: Asteroids are small, rocky remnants left over from the early formation of our solar system. They are classified into three primary types based on their spectral characteristics, which reflect their surface composition (albedo) and corresponding mineralogy:

C-type (Carbonaceous): These are the most abundant type, making up over 75% of known asteroids. They are very dark (low albedo) and composed of clay and silicate rocks, containing a high percentage of carbon. They are some of the oldest objects in the solar system.

S-type (Silicate/Stony): Accounting for about 17% of asteroids, these are relatively bright. They are composed mostly of silicate materials and nickel-iron, lacking significant carbon content. They dominate the inner asteroid belt.

M-type (Metallic): These are moderately bright and are primarily composed of metallic iron and nickel. They are believed to be the exposed cores of early, differentiated planetesimals that were shattered by impacts.

Question 4. Answer all the questions:

(a) What is the shape of the earth?

Ans: The shape of the Earth is an oblate spheroid (or oblate ellipsoid), meaning it is mostly spherical but slightly flattened at the poles and bulging at the equator due to its rotation.

(b) What is the mass of the earth?

Ans: The mass of the Earth is approximately 5.97 × 10²⁴ kg.

(c) Which is the largest terrestrial planet of our solar system?

Ans: Earth is the largest terrestrial planet in our solar system.

(d) Give two examples of Jovian planets.

Ans: Two examples of Jovian planets are Jupiter and Saturn (Uranus and Neptune are also correct).

(e) Define magnetosphere.

Ans: The magnetosphere is the region of space surrounding an astronomical object, such as Earth, in which charged particles (like those from the solar wind) are controlled and deflected by that object's magnetic field.

Question 5. Write short notes on any two of the following:

Note: Solutions for all three options are provided below for comprehensive study.

(a) Lithosphere

Ans: The lithosphere is the rigid, outermost rocky shell of the Earth.

Composition and Depth: It consists of the crust and the uppermost part of the solid mantle. It extends from the Earth's surface to a depth of approximately 100 km, though it can be thicker under old cratons and thinner at mid-ocean ridges.

Tectonic Significance: Based on its mechanical properties, the lithosphere behaves as a brittle, rigid solid over geological timescales. It is fragmented into tectonic plates (both oceanic and continental lithosphere) that glide over the hotter, more ductile asthenosphere below.

Dynamics: The creation, destruction, and movement of the lithosphere govern the principles of plate tectonics, driving earthquakes, volcanism, and mountain building.

(b) Gravitational field of the earth

Ans: The Earth's gravitational field is the field of attractive force surrounding the Earth, pulling objects toward its center of mass.

Mechanism: Governed by Newton's law of universal gravitation, the acceleration due to gravity on the Earth's surface averages about 9.8 m/s².

Variations: The field is not perfectly uniform. It varies across the Earth's surface due to two main factors:

Centrifugal Force: Earth's rotation causes a slight outward centrifugal force that counters gravity, making the gravitational pull slightly weaker at the equator than at the poles.

Mass Distribution: Uneven distribution of mass in the crust and mantle (e.g., mountains, dense ore bodies, ocean trenches) creates localized gravity anomalies.

Measurement: These anomalies are measured using gravimeters and are mapped as the geoid, which is the shape the ocean surface would take under the influence of gravity and rotation alone.

(c) Cryosphere

Ans: The cryosphere encompasses all the regions of the Earth's surface where water is in a solid form.

Components: This includes continental ice sheets (Greenland and Antarctica), mountain glaciers, ice caps, sea ice, lake and river ice, snow cover, and permafrost (frozen ground).

Role in Earth System: The cryosphere is a crucial component of the global climate system. It heavily influences the Earth's surface albedo (reflectivity); ice and snow reflect a significant amount of solar radiation back into space, helping to cool the planet.

Significance: It serves as the largest reservoir of freshwater on Earth. Fluctuations in the volume of the cryosphere directly control global eustatic sea levels and ocean circulation patterns.

Question 6. Define discontinuity. Describe the internal structure of the earth with suitable diagram. (1+3=4)

Ans:

Definition of Discontinuity: In seismology and geology, a discontinuity is a boundary or interface within the Earth's interior where there is a sudden and distinct change in the velocity of seismic waves (P-waves and S-waves). These abrupt shifts indicate a fundamental change in the chemical composition, density, or physical state (solid/liquid) of the earth's internal materials.

Internal Structure of the Earth: Based on chemical composition and seismic evidence, the Earth is divided into three primary concentric layers:

The Crust: The outermost, thinnest solid skin of the Earth. It is divided into:

Continental Crust: Thicker (average 30–50 km), less dense, and composed largely of granitic (felsic) rocks rich in silica and aluminum (Sial).

Oceanic Crust: Thinner (average 5–10 km), denser, and composed of basaltic (mafic) rocks rich in silica and magnesium (Sima).

The Mantle: The thickest layer, extending from the base of the crust to a depth of 2,900 km. It is composed of solid, dense, ultramafic rock (peridotite).

Upper Mantle: Includes the rigid lithospheric mantle and the underlying ductile asthenosphere, which allows for plate tectonic movement.

Lower Mantle (Mesosphere): Solid due to extreme pressure, despite high temperatures.

The Core: The innermost layer, composed primarily of an iron-nickel alloy (Nife). It is divided into two distinct parts based on physical state:

Outer Core (2900–5150 km): Liquid state. The convection of this liquid metallic layer generates the Earth's magnetic field.

Inner Core (5150–6371 km): Solid state due to immense pressure, despite possessing the highest temperatures in the Earth's interior.

Major Discontinuities separating these layers:

Mohorovičić Discontinuity (Moho): Separates the crust from the underlying mantle.

Gutenberg Discontinuity: Separates the lower mantle from the liquid outer core at 2,900 km depth. P-wave velocities drop sharply, and S-waves disappear entirely.

Lehmann Discontinuity: Separates the liquid outer core from the solid inner core at approximately 5,150 km.

Diagram Required: Internal Structure of the Earth.

Description: The student should draw a pie-slice or a cross-section of the Earth from the surface to the center.

Labels required:

Layers: Crust (Continental and Oceanic), Lithosphere, Asthenosphere, Lower Mantle, Outer Core, Inner Core.

Depths: 0 km (surface), ~35 km (Moho), 2900 km (Gutenberg Discontinuity), 5150 km (Lehmann Discontinuity), 6371 km (Center).

State: Label Outer core as "Liquid" and Inner core as "Solid".

Question 7. Fill in the blanks:

(a) The process in which rocks and minerals on the earth's surface are broken down into smaller pieces is called ________.

Ans: The process in which rocks and minerals on the earth's surface are broken down into smaller pieces is called weathering.

(b) ________ refers to the rate at which the temperature increases with depth in the earth's crust.

Ans: Geothermal gradient refers to the rate at which the temperature increases with depth in the earth's crust.

(c) S-waves travel only through ________.

Ans: S-waves travel only through solids.

(d) The theory of uniformitarianism was primarily proposed by ________.

Ans: The theory of uniformitarianism was primarily proposed by James Hutton (and later popularized by Charles Lyell).

(e) The earth's inner core is primarily composed of ________ and ________.

Ans: The earth's inner core is primarily composed of iron and nickel.

Question 8. Write short notes on any three of the following:

Note: Solutions for all five options are provided below for comprehensive study.

(a) Coriolis effect

Ans: The Coriolis effect is an apparent inertial force resulting from the Earth's rotation, causing moving objects or fluids to deflect from a straight path.

Mechanism: Because the Earth rotates eastward, and rotational velocity is higher at the equator than at the poles, moving masses of air or water are deflected.

Direction of Deflection: Objects are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Significance in Earth Sciences: It is a fundamental control on global atmospheric circulation (creating the trade winds and westerlies) and drives the major surface currents (gyres) in the world's oceans. It is also responsible for the rotation of cyclonic weather systems.

(b) Soil profile

Ans: A soil profile is a vertical cross-section of the soil that exposes its various horizons, extending from the ground surface down to the unweathered parent bedrock.

Horizons: A mature soil profile consists of distinct layers, typically labelled from top to bottom:

O Horizon: Surface litter and organic matter.

A Horizon (Topsoil): Rich in humus and minerals; a zone of intense biological activity.

E Horizon: Zone of eluviation (leaching) where minerals and clays are washed downward.

B Horizon (Subsoil): Zone of illuviation where leached minerals (like iron, clay, and calcium carbonate) accumulate.

C Horizon: Partially weathered parent rock material.

R Horizon: Unweathered bedrock.