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Q161. Bauxite formation is an example of metal enrichment by extreme:
Bauxite forms in hot, humid tropical climates where intense chemical weathering (leaching) removes soluble silica and cations from soils, leaving behind a highly concentrated residue of insoluble aluminum oxides.
Q162. A river channel widens downstream because the:
As a river flows downstream, tributaries add volume (increasing discharge). Concurrently, the slope flattens, reducing vertical downcutting and forcing the river's energy outward into lateral erosion, widening the channel.
Q163. Rivers in coastal regions world over got incised at around 18 ka mainly due to:
Around 18-20 thousand years ago (Last Glacial Maximum), global sea levels fell significantly, lowering the base level for coastal rivers and causing them to incise (cut down) into their beds.
Q164. Arrange the following ocean basins in the increasing order of surface salinity: A. Dead Sea, B. Red Sea, C. Mediterranean Sea, D. Arabian Sea
Arabian Sea has standard marine salinity (~36 PSU). Mediterranean is saltier due to restricted flow and evaporation (~38 PSU). Red Sea is extremely salty (~41 PSU). The Dead Sea is hypersaline (~340 PSU).
Q165. A seismic ray incident at an angle of 30° is refracted at an angle of 45°. If the velocity in the upper layer is v1 = 2.0 km/s, then the velocity in the underlying layer is close to (km/s):
Applying Snell's Law: sin(θ1)/v1 = sin(θ2)/v2. Therefore, sin(30°)/2.0 = sin(45°)/v2. This becomes 0.5/2.0 = 0.707/v2. Solving for v2 gives 0.707 / 0.25 = 2.828 km/s.
Q166. The largest negative radiative forcing of climate during the last two centuries is due to:
Anthropogenic aerosols (such as sulfur dioxide) scatter incoming sunlight and increase cloud reflectivity (albedo), providing a massive cooling effect (negative forcing) that has partially masked greenhouse gas warming.
Q167. The densest seawater is the:
Antarctic Bottom Water (AABW) is extremely cold and highly saline (due to brine rejection during sea ice formation), making it the densest water mass in the global ocean.
Q168. Plagioclase occurs in anorthosite as well as in granodiorite. The plagioclase composition in granodiorite is:
Anorthosite contains Calcium-rich plagioclase (Labradorite/Bytownite), while Granodiorite (being more felsic) contains Sodium-rich plagioclase (Oligoclase/Andesine).
Q169. With increasing amount of anthropogenic aerosols in the atmosphere, which one of the following statements is definitely correct?
Aerosols scatter and absorb incoming sunlight (a phenomenon known as global dimming). Therefore, an increase in aerosols definitively reduces the amount of direct solar radiation reaching the Earth's surface.
Q170. Which of the following tectonic settings is likely to yield detrital zircons with the least difference between their crystallization age and depositional age?
Active volcanic arcs at subduction zones produce zircons that are rapidly eroded and deposited into adjacent trenches, resulting in very similar ages.