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Q21. Gravity anomalies of value 0.1 mgal and 0.2 mgal are located at points separated by 300 m and 200 m respectively along a profile across a horizontal circular cylinder. The depth (in m) to the centre of the cylinder is:
This describes the width of the anomaly curve. Width at 0.2 mGal is 200m (x=100 from center). Width at 0.1 mGal is 300m (x=150). Equation: g = A*z / (x^2 + z^2). Setting up the ratio: 2 = (150^2 + z^2) / (100^2 + z^2). 2*(10000+z^2) = 22500+z^2, yielding z^2 = 2500, so z = 50m.
Q22. A seismic survey is carried out over alternating horizontal layers of shale and sandstone, each 0.5 km thick, with shale at the top. P-wave velocities are 2 km/s in shale and 4 km/s in sandstone. The stacking (RMS) velocity for a reflection from the base of the 5th layer is (km/s):
The wave travels through 3 shale layers and 2 sandstone layers. Time in shale = 3*(0.5/2) = 0.75s. Time in sand = 2*(0.5/4) = 0.25s. Total time = 1.0s. V_rms = sqrt( sum(v^2 * t) / sum(t) ) = sqrt( [3*(4*0.25) + 2*(16*0.125)] / 1.0 ) = sqrt(3 + 4) = sqrt(7) = 2.64 km/s.
Q23. Compared to the thickness of the oceanic lithosphere of 16 Ma, the oceanic lithosphere of 64 Ma would be:
The thickness of oceanic lithosphere increases proportionally to the square root of its age (Thickness ~ sqrt(t)). Since sqrt(64) / sqrt(16) = 8 / 4 = 2, the 64 Ma lithosphere is exactly twice as thick.
Q24. Ocean iron fertilization is considered as one of the potential means to decrease atmospheric carbon dioxide. Pick the INCORRECT statement:
The stoichiometric requirement of Iron to Nitrogen for marine phytoplankton (like diatoms) is extremely small, typically on the order of 1:1000 to 1:10,000, not 1:100. Iron is a trace micronutrient.
Q25. Relative to the deep ocean, the surface ocean has less dissolved CO2 because : A: deep ocean is cooler than the surface ocean. B: there is no primary production in the deep ocean. C: deep ocean has less oxygen relative to surface ocean. D: deep ocean is denser than the surface ocean
The solubility pump ensures colder deep waters can hold more dissolved gases (A). The biological pump ensures phytoplankton consume CO2 at the surface, while respiration adds CO2 in the deep ocean where no photosynthesis occurs (B).
Q26. The Bergeron process explains the growth of droplets from cloud to the size needed for rain due to the:
The saturation vapor pressure is lower over ice than over water. In mixed-phase clouds, this pressure gradient causes water droplets to evaporate and deposit onto ice crystals, allowing them to grow large enough to fall.
Q27. Off Chennai coast, the nitrate-nitrogen concentration is 16uM. Given the definitive Redfield ratio of C:N:P, which one of the following ratios is correct for phytoplankton uptake?
The Redfield Ratio is C:N:P = 106:16:1. If you multiply the entire ratio by 16, you get 1696:256:16. This matches the proportions exactly, keeping the fundamental uptake stoichiometry intact.
Q28. A and B are the directions of Natural Remanent Magnetization (NRM) in two deep sea sediment samples of ages 0.60 Ma and 1.20 Ma respectively. If N is the direction of the present day magnetic field, then:
The present day normal polarity (Brunhes chron) began 0.78 Ma. Therefore, the 0.60 Ma sample (A) formed during normal polarity (parallel to N), while the 1.20 Ma sample (B) formed during the Matuyama reversed chron (antiparallel to N).
Q29. Which of the following oceans/seas is decreasing in its total area for the past few million years?
The Pacific Ocean is shrinking because it is surrounded by destructive plate boundaries (subduction zones). The Atlantic and Red Sea are expanding due to divergent boundaries.
Q30. Which of the following events have contributed to establishment of permanent ice sheet of Antarctica?
The opening of the Drake Passage (between South America and Antarctica) and the Tasman Seaway allowed the Antarctic Circumpolar Current to form. This powerful current thermally isolated Antarctica, triggering massive glaciation.