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Q31. Considering the Indian plate movement in Late Cretaceous to Cenozoic, which of the following statements is true with respect to Ninety East Ridge?
The Ninety East Ridge is a hotspot track. As the Indian plate moved northward over the Kerguelen hotspot, the oldest basalts were deposited first (now at the northern end), leaving the youngest ones near the southern hotspot.
Q32. A is a gravity station at 45 degree N latitude and B is another station 20 km north of A. The measured gravity value at B is 16.2 mgal larger than that at A. Then the elevation at B is:
The latitude correction gradient at 45N is roughly 0.81 mGal/km. Moving 20 km north accounts for a 16.2 mGal increase (20 * 0.81). Since this perfectly matches the measured anomaly, the elevation effect must be zero.
Q33. Wave refraction around an island close to a main land interrupts the long shore current and creates a:
The island acts as a wave-break, slowing the longshore currents behind it. Sediment drops out of suspension, eventually building a sand bar that connects the island to the mainland, known as a tombolo.
Q34. The core of the Earth is determined to have formed during the first 30 Ma of its origin. This was estimated using radioactive dating of iron meteorites. Which of the methods would have been used for this purpose?
The Hafnium-Tungsten (Hf-W) short-lived chronometer is specifically used to date planetary core formation because Tungsten is highly siderophile (iron-loving) and sank to the core, while Hafnium is lithophile and stayed in the mantle.
Q35. In the energy budget of the Earth-atmosphere system, the largest component is:
The greenhouse effect involves the atmosphere absorbing vast amounts of longwave terrestrial (infrared) radiation. In terms of absolute energy flux within the system, this atmospheric absorption is the single largest component.
Q36. Because of the ellipticity of the Earth's orbit, solar radiation incident on the Earth is:
The Earth reaches perihelion (closest approach to the Sun) in early January. Therefore, the globally averaged incident solar radiation is about 7% higher during the December solstice compared to the June solstice.
Q37. A newly discovered planet has an atmosphere made of a gas whose specific heat cp is 1000 J/kg/K. If the lapse rate is 20 K/km, what is its acceleration due to gravity? (m/s2):
The dry adiabatic lapse rate is calculated as Gamma = g / cp. Converting 20 K/km to 0.02 K/m. 0.02 = g / 1000. Solving for g gives 20 m/s^2.
Q38. The Cenozoic Era has been marked by major climate changes caused by opening and closing of ocean gateways. Which one is generally associated with Northern Hemisphere glaciations?
The closing of the Isthmus of Panama (~3 Ma) diverted warm equatorial waters northward (strengthening the Gulf Stream), which provided the moisture necessary to build the massive Northern Hemisphere ice sheets.
Q39. Banded Iron Formations occur predominantly in the greenstone belts of the Dharwar Craton, such as Bababudan. Based on this, the correct inference is:
The Bababudan group is roughly 2.7 to 2.9 billion years old. Extensive BIFs indicate the oxygenation of the oceans by photosynthetic blue-green algae (cyanobacteria) around 2700 Ma.
Q40. A buried anomalous body in the form of a two-dimensional horizontal plate of width 4.0 km provides, on the Earth's surface, gravity anomalies of 0.6 mgal and 0.48 mgal, respectively, on its centre and edge. The maximum gravity anomaly produced by a plate of width 8.0 km of the same thickness, density contrast and depth would be (mgal):
The anomaly of an 8km plate at its center spans the exact same subsurface geometry as two 4km plates placed side-by-side measured from their shared edge. Thus, Anomaly = 2 * Edge Anomaly of 4km plate = 2 * 0.48 = 0.96 mGal.