Geology 2023 Paper I 50 marks Describe

Q2

(a) Describe the types of radiometric dating techniques used to establish the age of the Earth. (20 marks) (b) Discuss the different types of interaction of electromagnetic radiation with the atmosphere of the earth and its impact on remote sensing images. (15 marks) (c) What are joints ? Describe the Geometric and Genetic classification of joints with neat diagrams. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) पृथ्वी की आयु स्थापित करने के लिए उपयोग की जाने वाली रेडियोमितीय काल-निर्धारण तकनीकों के प्रकारों का वर्णन कीजिए । (20 अंक) (b) पृथ्वी के वातावरण के साथ विद्युत चुंबकीय विकिरण की विभिन्न प्रकार की पारस्परिक क्रियाओं एवं सुदूर संवेदी प्रतिबिंबों पर इसके प्रभाव की विवेचना कीजिए । (15 अंक) (c) संधि क्या है ? स्वच्छ आरेखों की सहायता से संधियों के ज्यामितीय एवं आनुवंशिक वर्गीकरण का वर्णन कीजिए । (15 अंक)

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Directive word: Describe

This question asks you to describe. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'describe' demands systematic, detailed exposition with appropriate technical depth. Allocate approximately 40% of time/words to part (a) given its 20 marks, covering U-Pb, Rb-Sr, Sm-Nd, and K-Ar methods with decay equations and half-lives; ~30% each to parts (b) and (c). For (b), structure by interaction type (scattering, absorption, refraction) linking to atmospheric windows and image quality. For (c), define joints clearly, then present geometric (strike, dip, orientation) and genetic (tension, shear, release) classifications with labeled diagrams. Conclude with applications of each concept.

Key points expected

  • Part (a): U-Pb zircon dating (most precise, 4.404 Ga Acasta gneiss), Rb-Sr whole-rock and mineral isochron, Sm-Nd model ages for mantle differentiation, K-Ar and Ar-Ar methods for volcanic rocks; mention concordia-discordia diagrams and closure temperature concept
  • Part (a): Numerical values—Earth age ~4.54 Ga, Canyon Diablo meteorite, Jack Hills zircons; limitations like daughter product loss, metamorphic resetting
  • Part (b): Rayleigh and Mie scattering (wavelength dependence, blue sky effect), selective absorption by H2O, CO2, O3 (atmospheric windows 0.4-2.5 μm, 8-14 μm), refraction causing geometric distortion; impact on Landsat/IRS image haze, contrast reduction, thermal band utility
  • Part (c): Definition of joints as fractures with no displacement, distinction from faults; geometric classification—strike/dip orientation (systematic vs. non-systematic, joint sets, joint systems with conjugate pairs)
  • Part (c): Genetic classification—tension joints (perpendicular to σ3, sheet joints in granites), shear joints (conjugate sets at ~30° to σ1), release/hybrid joints; field criteria for recognition (plumose structure, hackles, joint surface features)
  • Part (c): Neat labeled diagrams showing joint orientation in block diagrams, conjugate shear joint geometry, and tension joint propagation in folded rocks

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precisely explains decay systems (α, β, electron capture), correct half-life values, distinguishes radiogenic from initial Pb; accurately describes atmospheric scattering mechanisms and joint mechanics; no confusion between joints and faultsLists dating methods and joint types with minor errors in decay modes or atmospheric window boundaries; vague on shear vs. tension joint criteriaConfuses U-Pb with Th-Pb, misidentifies scattering types, treats joints as small faults, or omits closure temperature entirely
Diagram / cross-section20%10For (c): clean block diagrams showing joint sets in 3D, conjugate shear angles labeled with σ orientations, plumose structure detail; for (a): concordia-discordia curve sketch; for (b): atmospheric transmission curve with windows markedSimple 2D joint sketches without orientation labels, generic decay curve, or basic atmospheric layers diagram; diagrams present but not integrated with textNo diagrams for part (c) despite explicit demand, or unrecognizable sketches; missing concordia or transmission curves where essential
Field evidence15%7.5Cites Acasta gneiss (Canada), Jack Hills zircons (Australia), Vishnu basement rocks; mentions field recognition criteria—joint spacing in Deccan Traps columnar joints, plumose on sandstone; links joint patterns to stress regimes in Himalaya fold-thrust beltMentions generic field examples without specific localities; describes joint surface features without linking to formation mechanismNo field examples; purely theoretical treatment; confuses laboratory dating protocols with field sampling strategy
Quantitative reasoning20%10States decay equations (N=N₀e^(-λt)), calculates ages using isochron slopes, gives half-lives (U-238: 4.468 Ga, K-40: 1.25 Ga); quantifies scattering (λ^-4 dependence), gives wavelength ranges for atmospheric windows; joint angles with σ orientations (45°-φ/2 for shear)Mentions half-lives without equations, gives approximate wavelength ranges, states joint angles without derivationNo numerical values; cannot write decay equation; confuses wavelength and frequency relationships in scattering
Indian / economic relevance20%10For (a): Ar-Ar dating of Rajmahal Traps, Sm-Nd ages of Dharwar craton; for (b): IRS/Landsat applications in Indian agriculture, atmospheric correction for RISAT; for (c): joint control on groundwater in Deccan basalts, quarrying in Rajasthan granites, slope stability in HimalayaMentions Indian remote sensing satellites or Deccan Traps without specific application; generic economic importance of jointsNo Indian examples; Western-centric examples only; ignores economic significance of joint systems in mining and hydrogeology

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