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Q71. Rayleigh waves have:
Rayleigh waves are surface waves where particle motion is a retrograde ellipse. They are slightly slower than body shear waves, typically travelling at about 0.9 times the local S-wave velocity.
Q72. Which of the following isotopes would be the most useful to study the Earth process that has time scales of 1000 years?
Radiometric dating is effective for timescales roughly between 0.1 and 10 times the isotope's half-life. For a 1000-year process, 14C (5730 years) is the only appropriate chronometer listed.
Q73. The radiogenic heat produced by 1 kg of rock is maximum for:
Radioactive heat-producing elements (U, Th, K) are highly incompatible. During partial melting, they strongly partition into the melt, enriching felsic rocks like granite far more than mafic/ultramafic rocks.
Q74. If Vm, Vo and Vi are the average P-wave velocities in the lower mantle, outer core and inner core respectively, then:
P-waves travel fastest in the deep, solid lower mantle (~13.7 km/s). Velocity drops sharply in the liquid outer core (~8 km/s), and rises again in the solid inner core (~11.2 km/s).
Q75. Coarsening upward sequence is a characteristic of:
Prograding deltas deposit coarser sands over finer prodelta muds as they build outwards, creating a classic coarsening upward sequence.
Q76. Primary productivity in the ocean refers to:
Primary productivity strictly refers to the 'rate' at which photosynthetic marine organisms (phytoplankton) convert dissolved inorganic CO2 into organic carbon within the photic (sunlit) zone.
Q77. The universal expression for water column production is:
Primary production is standardized as milligrams of carbon fixed per square meter (integrated across the depth of the photic zone) per day, allowing averaging over the day-night cycle.
Q78. The three main factors that conspire to form ozone hole are:
Polar stratospheric clouds (PSCs) provide the surface for chemical reactions, CFCs provide the destructive chlorine, and sunlight acts as the catalyst to drive the ozone-depleting reaction.
Q79. Which of the following rocks makes most of the upper mantle of the Earth?
Peridotite, an ultramafic rock composed mostly of olivine and pyroxene, is the dominant rock type constituting the Earth's upper mantle.
Q80. An elevated land mass attaining isostatic compensation:
Over-compensation means the crustal root is too large for the surface topography, generating excess buoyancy that forces the landmass to uplift to attain equilibrium. Under-compensation leads to subsidence.