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CHSE Odisha Elective Geology study materials
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CHSE Odisha Elective Geology practice questions

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Question 1Geology (Elective)

In the geological time scale, the Phanerozoic eon is subdivided, from oldest to youngest, into which three eras?

  1. Archaean, Proterozoic, Palaeozoic
  2. Palaeozoic, Mesozoic, Cenozoic Correct answer.
  3. Mesozoic, Palaeozoic, Cenozoic
  4. Cenozoic, Mesozoic, Palaeozoic

Explanation

The Phanerozoic ('visible life') eon is conventionally divided into the Palaeozoic, Mesozoic and Cenozoic eras, in that chronological order. The Archaean and Proterozoic belong to the Precambrian, which precedes the Phanerozoic.

Question 2Geology (Elective)

A mineral that breaks along smooth, flat, parallel surfaces related to planes of weak atomic bonding is said to possess which property?

  1. Fracture
  2. Lustre
  3. Cleavage Correct answer.
  4. Tenacity

Explanation

Cleavage is the tendency of a mineral to split along definite crystallographic planes where atomic bonding is weakest, producing flat shiny surfaces. Fracture, by contrast, describes breakage on irregular surfaces with no preferred plane.

Question 3Geology (Elective)

Which rock type forms by the cooling and solidification of molten material?

  1. Metamorphic rock
  2. Clastic rock
  3. Igneous rock Correct answer.
  4. Sedimentary rock

Explanation

Igneous rocks crystallise from magma or lava as it cools, giving either intrusive (coarse-grained) or extrusive (fine-grained) textures. Sedimentary and metamorphic rocks form by deposition and by solid-state recrystallisation respectively.

Question 4Geology (Elective)

The Mohorovičić discontinuity (Moho) marks the boundary between which two layers of the Earth?

  1. Crust and mantle Correct answer.
  2. Lithosphere and asthenosphere
  3. Outer core and inner core
  4. Mantle and outer core

Explanation

The Moho is the seismic discontinuity at which P-wave velocities jump sharply, marking the base of the crust and the top of the mantle. It lies at roughly 5–10 km depth beneath oceans and 30–70 km beneath continents.

Question 5Geology (Elective)

Which seismic wave type is a longitudinal (compressional) body wave that travels fastest and can pass through both solids and fluids?

  1. Love wave
  2. S wave
  3. P wave Correct answer.
  4. Rayleigh wave

Explanation

P waves are compressional body waves in which particle motion is parallel to the direction of propagation, making them the fastest seismic waves and able to travel through liquids. S waves are transverse and cannot propagate through fluids.

Question 6Geology (Elective)

Which of the following is the hardest mineral on the Mohs scale?

  1. Topaz
  2. Quartz
  3. Diamond Correct answer.
  4. Corundum

Explanation

Diamond has a Mohs hardness of 10, the top of the scale, because of its tightly bonded three-dimensional carbon framework. Corundum (9), topaz (8) and quartz (7) are all softer.

Question 7Geology (Elective)

A fold in which the rock strata are arched upward, with the oldest beds exposed in the core, is called a:

  1. Syncline
  2. Monocline
  3. Anticline Correct answer.
  4. Basin

Explanation

An anticline is an upward-arching fold whose eroded core exposes the oldest strata, because the limbs dip away from the axis. A syncline is the complementary downward fold with the youngest beds in its core.

Question 8Geology (Elective)

The mineral calcite is identified by which chemical formula?

  1. NaCl
  2. SiO2
  3. FeS2
  4. CaCO3 Correct answer.

Explanation

Calcite is calcium carbonate, CaCO3, the principal mineral of limestone and marble; it fizzes readily in dilute hydrochloric acid. The other formulae correspond to quartz, pyrite and halite respectively.

Question 9Geology (Elective)

Which of the following best describes a transform plate boundary?

  1. Two continental plates collide and thicken the crust
  2. Two plates move apart and new oceanic lithosphere is created
  3. Two plates slide horizontally past one another, generating shallow-focus earthquakes Correct answer.
  4. An oceanic plate descends beneath a continental plate

Explanation

At a transform boundary lithospheric plates move laterally past each other with neither creation nor destruction of crust, producing strike-slip faulting and shallow earthquakes. The San Andreas Fault is a classic example.

Question 10Geology (Elective)

A sedimentary rock composed mainly of well-rounded, well-sorted sand grains cemented by silica is best classified as:

  1. Greywacke
  2. Quartz arenite (orthoquartzite) Correct answer.
  3. Shale
  4. Conglomerate

Explanation

A well-sorted, rounded, quartz-rich sandstone with a siliceous cement is a quartz arenite, reflecting prolonged transport and reworking. Greywacke is poorly sorted and muddy, shale is fine-grained, and conglomerate contains gravel-size clasts.

Question 11Geology (Elective)

In the crystallographic systems, a mineral with three mutually perpendicular axes of unequal length belongs to which system?

  1. Orthorhombic Correct answer.
  2. Tetragonal
  3. Triclinic
  4. Cubic

Explanation

The orthorhombic system has three axes at 90° to each other but all of different lengths. The cubic system has three equal axes at 90°, and tetragonal has two equal horizontal axes with a different vertical axis.

Question 12Geology (Elective)

Which metamorphic facies is characterised by the assemblage garnet + clinopyroxene + plagioclase in mafic rocks at high pressure and high temperature?

  1. Eclogite facies Correct answer.
  2. Hornblende hornfels facies
  3. Zeolite facies
  4. Greenschist facies

Explanation

Eclogite facies forms at high pressure and temperature, where mafic compositions recrystallise to garnet plus omphacitic clinopyroxene with no plagioclase. It is typical of deeply subducted oceanic crust.

Question 13Geology (Elective)

An ore mineral of lead that is a sulphide with the formula PbS is:

  1. Sphalerite
  2. Chalcopyrite
  3. Galena Correct answer.
  4. Hematite

Explanation

Galena is lead sulphide, PbS, the chief ore of lead, and is notable for its cubic cleavage and metallic lustre. Sphalerite is ZnS, chalcopyrite is CuFeS2, and hematite is Fe2O3.

Question 14Geology (Elective)

A fault in which the hanging wall has moved down relative to the footwall is termed a:

  1. Thrust fault
  2. Reverse fault
  3. Strike-slip fault
  4. Normal fault Correct answer.

Explanation

In a normal fault the hanging wall moves down relative to the footwall, a response to extension. Reverse and thrust faults show the opposite sense of movement under compression, and strike-slip faults involve lateral displacement.

Question 15Geology (Elective)

The process by which loose sediment is converted into solid rock through compaction and cementation is called:

  1. Weathering
  2. Diagenesis of magma
  3. Metamorphism
  4. Lithification Correct answer.

Explanation

Lithification is the conversion of unconsolidated sediment into coherent rock, chiefly by compaction and cementation by minerals such as calcite or silica. It is a key step in the rock cycle after deposition.

Question 16Geology (Elective)

Which unconformity represents a surface where sedimentary strata overlie igneous or metamorphic rocks that were exposed and eroded before deposition resumed?

  1. Disconformity
  2. Paraconformity
  3. Nonconformity Correct answer.
  4. Angular unconformity

Explanation

A nonconformity separates sedimentary strata from underlying igneous or metamorphic basement, showing that the older crystalline rock was exposed and eroded before the sediments were laid down. Angular unconformities involve tilted strata, and disconformities separate parallel sedimentary beds.

Question 17Geology (Elective)

Radiometric dating using the decay of potassium-40 to argon-40 is especially useful for dating which materials?

  1. Fossil shells composed of calcium carbonate
  2. Deep-sea carbonate ooze
  3. Organic remains such as wood and bone
  4. Volcanic rocks and micas that cooled rapidly Correct answer.

Explanation

Potassium-argon dating relies on argon gas being trapped only after a mineral cools below its closure temperature, so it dates volcanic rocks and micas that cooled rapidly. It is unsuitable for carbonate or organic material, which lacks the required potassium-bearing lattice.

Question 18Geology (Elective)

Which of the following describes the change in apparent polar-wander paths that provided early support for continental drift?

  1. Paths from all continents coincide exactly regardless of reconstruction
  2. Paths from ocean basins are always longer than those from continents
  3. Paths from different continents diverge when plotted on a fixed continent but converge when continents are reassembled Correct answer.
  4. Paths from different continents are identical in shape but differ in age

Explanation

Apparent polar-wander paths differ between continents when each is held fixed, but align when the continents are restored to a Pangaea-like configuration. This agreement was strong independent evidence for continental drift and later plate tectonics.

Question 19Geology (Elective)

A rock sample contains 25% of its original radioactive parent isotope. How many half-lives have elapsed?

  1. Three
  2. Two Correct answer.
  3. One
  4. Four

Explanation

After one half-life 50% of the parent remains, after two 25%, after three 12.5% and after four 6.25%. A remaining fraction of 25% therefore corresponds to two half-lives.

Question 20Geology (Elective)

Which of the following fossil groups is most useful as a zone fossil for correlating marine Jurassic strata?

  1. Trilobites
  2. Graptolites
  3. Stromatolites
  4. Ammonites Correct answer.

Explanation

Ammonites underwent rapid evolution and had wide geographic distribution, so they are the standard zone fossils for Jurassic and Cretaceous marine correlation. Trilobites are mainly Palaeozoic, graptolites mainly Ordovician–Silurian, and stromatolites are long-ranging.

Question 21Geology (Elective)

In a coastal environment, a sequence of sedimentary rocks shows a transition from conglomerate at the base through sandstone to shale at the top. This is best interpreted as:

  1. A fining-upward sequence deposited in a progressively deeper or lower-energy setting Correct answer.
  2. A metamorphic gradient unrelated to deposition
  3. A coarsening-upward sequence deposited in a shallowing environment
  4. A single storm deposit with no vertical trend

Explanation

The grain size decreases upward from conglomerate to shale, indicating a fining-upward trend in which energy decreased and the environment deepened over time. Such trends are used to interpret transgressive successions and channel abandonment.

Question 22Geology (Elective)

Which type of plate boundary is most directly associated with the formation of island arcs such as those of the western Pacific?

  1. Mid-ocean ridge boundary
  2. Transform boundary
  3. Ocean–ocean convergent boundary Correct answer.
  4. Continental rift boundary

Explanation

When two oceanic plates converge, one subducts, and partial melting of the mantle wedge generates magmas that build a chain of volcanic islands above the Benioff zone. This produces the island arcs of the western Pacific.

Question 23Geology (Elective)

A mineral has a specific gravity of about 7.5, metallic lustre, and a dark grey streak; it is the chief ore of lead. Which mineral is it?

  1. Barite
  2. Graphite
  3. Galena Correct answer.
  4. Magnetite

Explanation

Galena (PbS) is dense for a common mineral, with specific gravity near 7.5, has a metallic lustre, a grey streak and cubic cleavage, and is the principal lead ore. Magnetite is an iron oxide, barite is a sulphate, and graphite is a soft native carbon mineral.

Question 24Geology (Elective)

In the context of stratigraphic correlation, which principle states that a sedimentary layer is older than the layer above it and younger than the layer below it?

  1. Principle of faunal succession
  2. Principle of superposition Correct answer.
  3. Principle of cross-cutting relationships
  4. Principle of lateral continuity

Explanation

The principle of superposition states that in an undisturbed sequence, each layer is older than the one above it and younger than the one below it. It is the fundamental basis for relative dating of stratified rocks.

Question 25Geology (Elective)

A metamorphic rock with a strong planar fabric formed by the parallel alignment of platy minerals such as mica is described as:

  1. Granoblastic
  2. Massive
  3. Foliated Correct answer.
  4. Porphyroblastic

Explanation

Foliation is a planar fabric produced by the preferred orientation of platy or prismatic minerals under directed pressure, typical of slate, schist and gneiss. Granoblastic and massive textures lack such a preferred alignment.

Question 26Geology (Elective)

Which mineral property is defined as the colour of a mineral's powder when it is rubbed across an unglazed porcelain plate?

  1. Streak Correct answer.
  2. Lustre
  3. Tenacity
  4. Cleavage

Explanation

Streak is the colour of the fine powder left by a mineral, and it is often more diagnostic than the colour of the bulk specimen because it is less affected by surface weathering or impurities. It is tested on an unglazed porcelain streak plate.

Question 27Geology (Elective)

A magma that crystallises at depth over a long period, allowing large crystals to grow, will most likely produce which rock texture?

  1. Vitreous
  2. Phaneritic Correct answer.
  3. Porphyritic
  4. Aphanitic

Explanation

Slow cooling at depth gives crystals time to grow large enough to be seen with the naked eye, producing a coarse-grained or phaneritic texture typical of plutonic rocks such as granite. Rapid cooling near the surface instead yields fine grains.

Question 28Geology (Elective)

Which type of volcano is built mainly from alternating layers of lava flows and pyroclastic material and is typically steep-sided and associated with explosive eruptions?

  1. Shield volcano
  2. Lava dome
  3. Stratovolcano Correct answer.
  4. Cinder cone

Explanation

A stratovolcano, or composite volcano, forms from repeated alternation of viscous lava flows and explosive ash and pyroclastic deposits, giving it a layered structure and steep profile. Andesitic magma and subduction settings are typical.

Question 29Geology (Elective)

A rock sample is scratched easily by a copper coin but not by a fingernail. On the Mohs scale, the mineral most likely has a hardness of about:

  1. 9
  2. 7
  3. 1
  4. 3 Correct answer.

Explanation

Fingernail hardness is about 2.5 and a copper coin is about 3 to 3.5, so a mineral scratched by the coin but not by a fingernail falls near 3. Calcite, with hardness 3, is a classic example.

Question 30Geology (Elective)

Which sedimentary structure indicates deposition from a current that was weakening over time?

  1. Ripple marks
  2. Cross-bedding
  3. Mud cracks
  4. Graded bedding Correct answer.

Explanation

Graded bedding shows a gradual upward decrease in grain size, recording deposition from a current that lost energy, as in a turbidity current. The coarse grains settle first and finer material follows.

Question 31Geology (Elective)

Which agent of metamorphism is most directly responsible for the development of foliation in a pelitic rock?

  1. Directed pressure Correct answer.
  2. Radioactive heating
  3. Pore-fluid chemistry
  4. Rising temperature alone

Explanation

Directed or differential pressure causes platy and prismatic minerals such as mica to grow with a preferred orientation, producing foliation. Temperature alone promotes recrystallisation and mineral reactions but not the alignment that defines foliation.

Question 32Geology (Elective)

Which of the following best describes the nature of the Mohorovičić discontinuity?

  1. A boundary between the crust and the mantle marked by a sharp increase in seismic velocity Correct answer.
  2. A boundary within the mantle where seismic velocity decreases sharply
  3. A boundary between the lithosphere and the asthenosphere
  4. A boundary between the outer and inner core

Explanation

The Mohorovičić discontinuity, or Moho, is the base of the crust where P-wave velocity jumps to about 8 km/s in the underlying mantle. It is recognised seismically and lies at variable depth, deeper beneath continents than beneath oceans.

Question 33Geology (Elective)

Which of the following is the most characteristic field test for confirming that a mineral is carbonate, such as calcite?

  1. Greenish streak on porcelain
  2. Effervescence with dilute hydrochloric acid Correct answer.
  3. Magnetic attraction to a hand magnet
  4. Taste of saltiness

Explanation

Carbonate minerals such as calcite react with dilute hydrochloric acid and release carbon dioxide, producing visible effervescence. This is a quick and reliable field test for carbonates.

Question 34Geology (Elective)

In the geological time scale, which era is characterised by the first appearance of abundant hard-shelled marine invertebrates and the first land plants?

  1. Archaean
  2. Palaeozoic Correct answer.
  3. Cenozoic
  4. Mesozoic

Explanation

The Palaeozoic Era records the appearance and diversification of hard-shelled marine invertebrates, early fishes, and later the colonisation of land by plants and vertebrates. It ends with the Permian mass extinction.

Question 35Geology (Elective)

A sequence of sedimentary beds is cut by an igneous dyke that does not extend into the overlying beds. Which principle allows us to say the dyke is younger than the beds it cuts?

  1. Superposition
  2. Faunal succession
  3. Original horizontality
  4. Cross-cutting relationships Correct answer.

Explanation

The principle of cross-cutting relationships states that a feature which cuts across another must be younger than the feature it cuts. A dyke that truncates bedding is therefore younger than the beds.

Question 36Geology (Elective)

Which of the following describes a normal fault in terms of stress and movement?

  1. Compression causes the hanging wall to move up relative to the footwall
  2. Extension causes the hanging wall to move down relative to the footwall Correct answer.
  3. Shear causes horizontal displacement along a vertical fault plane
  4. Extension causes the footwall to move down relative to the hanging wall

Explanation

Normal faults form under extensional stress, and the hanging wall moves downward relative to the footwall. They are common in rift valleys and continental rifts.

Question 37Geology (Elective)

Which seismic wave type is a compressional body wave that travels fastest and can pass through both solids and fluids?

  1. S-wave
  2. Rayleigh wave
  3. Love wave
  4. P-wave Correct answer.

Explanation

P-waves are longitudinal compressional waves and the fastest seismic body waves, propagating through solids, liquids and gases. Their arrival is recorded first on a seismogram.

Question 38Geology (Elective)

A mineral shows two sets of cleavage planes intersecting at about 90 degrees, with good cleavage in both directions. Which mineral is most consistent with this description?

  1. Muscovite mica
  2. Orthoclase feldspar Correct answer.
  3. Calcite
  4. Quartz

Explanation

Orthoclase feldspar has two cleavages at approximately right angles, producing blocky fragments. This distinguishes it from micas, which have one perfect cleavage, and from quartz, which lacks cleavage.

Question 39Geology (Elective)

Which process is the main way that groundwater dissolves limestone to form caves and karst topography?

  1. Hydration of feldspar
  2. Carbonic acid dissolving calcium carbonate Correct answer.
  3. Oxidation of iron minerals
  4. Mechanical abrasion by sand

Explanation

Rainwater absorbs carbon dioxide to form weak carbonic acid, which dissolves calcium carbonate in limestone along joints and bedding planes, enlarging them into caves and producing karst features.

Question 40Geology (Elective)

Which of the following best explains why the oceanic crust is systematically younger than the continental crust?

  1. Oceanic crust is denser and therefore older
  2. Continental crust forms only during the Precambrian
  3. Oceanic crust is continually created at mid-ocean ridges and destroyed at subduction zones Correct answer.
  4. Oceanic crust is protected from erosion by seawater

Explanation

Sea-floor spreading creates new oceanic lithosphere at mid-ocean ridges, while older oceanic lithosphere is consumed at subduction zones. This recycling keeps most oceanic crust younger than about 200 million years.

Question 41Geology (Elective)

Which of the following fossil groups is most characteristic of Palaeozoic shallow marine strata and is widely used for correlation because of its rapid evolution?

  1. Ammonites
  2. Trilobites
  3. Graptolites Correct answer.
  4. Nummulites

Explanation

Graptolites are colonial planktonic organisms whose rapidly evolving forms make them excellent zone fossils for correlating Palaeozoic, especially Ordovician to Silurian, marine strata. Their wide geographic distribution adds to their value.

Question 42Geology (Elective)

A rock composed almost entirely of the mineral olivine, with a granular texture and dark green colour, is best named:

  1. Basalt
  2. Dunite Correct answer.
  3. Gabbro
  4. Peridotite

Explanation

Dunite is an ultramafic rock made almost entirely of olivine, with little or no pyroxene. Peridotite is a broader term for ultramafic rocks containing both olivine and pyroxene.

Question 43Geology (Elective)

Which type of unconformity is represented by a surface where tilted or folded sedimentary beds are overlain by flat-lying younger beds?

  1. Angular unconformity Correct answer.
  2. Nonconformity
  3. Paraconformity
  4. Disconformity

Explanation

An angular unconformity forms when older tilted or folded strata are eroded and then buried by younger horizontal beds, so the two sets meet at an angle. It records deformation followed by erosion and renewed deposition.

Question 44Geology (Elective)

Which of the following is the most likely explanation for the presence of marine fossils in sedimentary rocks now exposed high in the Himalayas?

  1. The organisms lived in freshwater lakes at high altitude
  2. The rocks were deposited below sea level and later uplifted by tectonic convergence Correct answer.
  3. The rocks formed by metamorphism of seawater
  4. The fossils were carried there by rivers from the sea

Explanation

Marine fossils in Himalayan rocks show that these strata were deposited on the sea floor and later raised by the collision of India with Asia. Uplift and folding during mountain building brought them to high elevation.

Question 45Geology (Elective)

Which of the following statements about the Deccan Traps is accurate?

  1. They are Mesozoic marine shales of the east coast
  2. They are Precambrian granites exposed in the Aravalli region
  3. They are flood basalts erupted near the Cretaceous-Palaeogene boundary in peninsular India Correct answer.
  4. They are Palaeozoic limestones of the Himalayan region

Explanation

The Deccan Traps are extensive flood basalts of Late Cretaceous to early Palaeogene age in peninsular India, erupted around the time of the Cretaceous-Palaeogene boundary. They form a major igneous province in Indian geology.

Question 46Geology (Elective)

In a metamorphic terrain, a pelitic rock shows a sequence from slate to phyllite to schist to gneiss as temperature and pressure increase. Which feature best marks the change from slate to phyllite?

  1. Development of a silky sheen from coarser mica Correct answer.
  2. Complete loss of foliation
  3. Growth of centimetre-scale augen feldspar
  4. Appearance of garnet porphyroblasts

Explanation

Phyllite is distinguished from slate by a silky sheen caused by coarser, recrystallised mica, and by a more wavy cleavage. The increase in grain size reflects a higher grade of metamorphism.

Question 47Geology (Elective)

A rock has 12.5% of its original radioactive parent isotope remaining. How many half-lives have elapsed?

  1. 3 Correct answer.
  2. 4
  3. 2
  4. 5

Explanation

After each half-life the parent fraction halves: 50%, then 25%, then 12.5%. Reaching 12.5% therefore requires three half-lives.

Question 48Geology (Elective)

A mineral deposit is described as a placer. Which of the following best explains its formation?

  1. Hydrothermal fluids precipitating sulphides in fractures
  2. Magmatic segregation of heavy oxides at the base of a magma chamber
  3. Dense, resistant minerals concentrated by flowing water after lighter material is removed Correct answer.
  4. Chemical precipitation from evaporating seawater

Explanation

Placers form when weathering releases resistant, dense minerals such as gold, cassiterite or diamond, and flowing water winnows away lighter material, concentrating the heavy grains in stream or beach deposits.

Question 49Geology (Elective)

Which of the following best explains why the depth to the Moho is greater beneath continents than beneath oceans?

  1. Continents are colder and therefore conduct seismic waves faster
  2. Oceans have no mantle beneath them
  3. Oceanic crust is thicker and pushes the Moho deeper
  4. Continents are underlain by thicker, less dense crust in isostatic balance with the mantle Correct answer.

Explanation

Continental crust is thicker and less dense than oceanic crust, and it floats higher in isostatic equilibrium, so the crust-mantle boundary lies deeper beneath continents, commonly 30 to 70 km, than beneath oceans, where it is about 7 to 10 km.

Question 50Geology (Elective)

In a sedimentary basin, a sandstone bed contains grains that are angular and poorly sorted, while an overlying bed contains well-rounded, well-sorted grains. Which interpretation is most reasonable?

  1. The lower bed experienced longer transport than the upper bed
  2. The lower bed was deposited closer to its source and the upper bed after longer transport Correct answer.
  3. Both beds were deposited by the same current without change
  4. The lower bed was deposited in deeper water than the upper bed

Explanation

Angular, poorly sorted grains indicate short transport and rapid deposition near the source, whereas well-rounded, well-sorted grains indicate longer transport and winnowing. The upward change therefore suggests a shift toward a more distal or higher-energy sorting environment.