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Q41. Which of the following is a body fossil?
Fossils are divided into 'trace fossils' (evidence of behavior, like footprints or fossilized poop) and 'body fossils' (remains of the actual creature's shape). When a shell dissolves and leaves a hollow mold in the rock, and that mold later fills with new minerals, it creates a 3D replica of the animal's body called a 'cast'.
Q42. Which of the following is an amorphous variety of SiO2?
'Amorphous' means something lacks a neat, orderly internal crystal structure (it is built more randomly like glass). While Quartz, Citrine, and Agate are all structured crystals made of silica (SiO2), 'Opal' is an amorphous form of silica that contains water and has no organized crystal grid.
Q43. Which of the following is the correct decreasing order of abundance of elements in our solar system?
The universe and our solar system are overwhelmingly made of the lightest element, Hydrogen (H), followed by Helium (He). After these two gases, Oxygen (O) is the next most common, followed by heavier elements like Iron (Fe). Therefore, the correct decreasing order is Hydrogen, then Helium, then Oxygen, then Iron.
Q44. Which of the following is the precursor of petroleum?
Before oil and gas (petroleum) are formed, dead algae and plankton get buried and heated up underground. The first thing they turn into is a solid, waxy, organic substance called 'kerogen'. If the kerogen gets heated even more, it eventually 'cooks' into liquid petroleum.
Q45. Which one of the following textures is found in alkali olivine basalt?
Basalt is a dark volcanic rock. When we look at 'alkali olivine basalt' under a microscope, we often see a specific pattern where tiny spaces between small, needle-like feldspar crystals are filled with other minerals like pyroxene or olivine. This 'between-the-grains' arrangement is called an 'intergranular' texture.
Q46. Which one of the metamorphic facies sequence in order of increasing metamorphic grade defines thermal metamorphism ?
'Thermal metamorphism' happens when rock is baked by nearby hot magma. As you get closer to the magma, the temperature (grade) gets hotter. The sequence starts at lower temperatures with albite-epidote, gets hotter to form hornblende, hotter still for pyroxene, and reaches the most extreme, blistering heat right next to the magma to form the sanidinite facies.
Q47. A pelitic rock consisting of cordierite + garnet + K-feldspar + sillimanite belongs to which one of the following metamorphic facies?
The correct answer is Granulite. Metamorphic 'facies' represent different levels of heat and pressure. The presence of these specific minerals, especially the lack of water-bearing minerals (like mica) and the presence of K-feldspar and sillimanite, indicates the rock was baked at extremely high temperatures, defining the 'Granulite' facies. Eclogite requires extreme pressure (not typical for cordierite). Greenschist and Blueschist are much lower temperature facies characterized by minerals like chlorite and glaucophane respectively, making them incorrect.
Q48. A plutonic igneous rock is composed of 50% orthopyroxene, 45% olivine and 5% clinopyroxene. What is the appropriate name of the rock according to the IUGS classification?
The correct answer is Harzburgite. The rock has more than 40% olivine, making it a peridotite. Inside the peridotite family, a rock that is mostly olivine and orthopyroxene is specifically called a Harzburgite. Norite and Troctolite have lots of plagioclase (which is missing here), and Wehrlite is dominated by clinopyroxene, not orthopyroxene, making them incorrect.
Q49. As per Ramsay’s classification of folds, the maximum thickening of fold hinge and the maximum thinning of the fold limbs are observed in ____________.
The correct answer is Class 3. In Ramsay's 'Class 3' folds, the rock material squishes and flows tremendously towards the bend (hinge), making the hinge very thick, while the sides (limbs) stretch out and become extremely thin. Class 1 folds either keep their thickness or thicken slightly, and Class 2 folds maintain the exact same vertical thickness everywhere, making them incorrect.
Q50. Crustal thickness is maximum at the ___________.
The correct answer is continent-continent convergent plate boundary. Earth's crust gets thickest when two massive continental plates crash into each other, folding and stacking the rock upwards to form massive mountain ranges. Ocean plates are too thin to create maximum thickness. Divergent boundaries are where plates pull apart, making the crust thinner, not thicker, so those options are wrong.