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Q131. During a glacial stage, the average salinity of the ocean:
During glaciation, vast quantities of fresh water are trapped on land as ice sheets. Removing this fresh water from the global hydrologic cycle concentrates the salts in the remaining ocean, increasing average salinity.
Q132. Average salinity of the oceans during the glacial periods:
During glacial periods, massive volumes of freshwater evaporate from the oceans and get locked up as continental ice sheets. Removing this freshwater concentrates the remaining salts, increasing overall oceanic salinity.
Q133. How does El Nino influence atmospheric CO2 levels?
During El Nino, widespread severe droughts occur across major tropical rainforests. This drastically increases forest fires and heterotrophic respiration while suppressing photosynthesis, causing a net spike in atmospheric CO2.
Q134. Compared to that on the surface, the Earth's gravity field at the core-mantle boundary is:
Due to the high density of the core, Earth's gravity actually increases slightly with depth through the mantle, peaking near the Core-Mantle Boundary.
Q135. A geophysicist travelling from the Bay of Bengal through the Ganga plain to the Himalaya, estimates the depth of Moho discontinuity. Which one of the following is the correct order of the Moho-depth estimates?
Due to isostasy, high mountain ranges like the Himalayas have extremely deep crustal roots (~70km). Continental plains have average crust (~35km), while oceanic crust is the thinnest (~7-10km).
Q136. At high pressures and temperatures rocks undergo permanent ductile deformation under tectonic stresses. Such permanent strains can develop when the stress in the rocks reaches its:
Ductile (plastic) deformation begins precisely when the applied stress exceeds the elastic limit, also known as the yield strength of the rock.
Q137. When a parcel of air descends from height:
Descending air undergoes adiabatic compression due to increasing atmospheric pressure, which reduces its volume and raises its temperature.
Q138. In comparison with normal river flow, debris flows can easily carry large boulders because of higher:
Debris flows act as a non-Newtonian fluid. Their high sediment concentration drastically increases their density and viscosity, providing immense buoyant and cohesive forces capable of suspending massive boulders.
Q139. Among marine crustaceans, the largest number of species are known from the order:
Copepods are arguably the most numerous multicellular organisms in the entire ocean. They represent the largest number of marine crustacean species and form a critical link in the marine food web.
Q140. The Young's modulus of a rock specimen of density 2.7 gm/cc is 9.72 megabars. The longitudinal wave velocity (in km/s) in the rock is:
Converting units: 1 bar = 10^6 dynes/cm2. 9.72 Mbar = 9.72 x 10^12 dynes/cm2. Using the 1D velocity equation V = sqrt(E / density): V = sqrt(9.72 x 10^12 / 2.7) = sqrt(3.6 x 10^12). This evaluates to 6 x 10^5 cm/s, which is exactly 6.0 km/s.