Consider the following statements: Fossils are primarily found in ...
Correct Answer:
a) 2 only
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Explanation:
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- Fossils are primarily found in sedimentary rocks:
Fossils are indeed primarily found in sedimentary rocks, as these rocks are formed from the accumulation of sediments over time, which can contain preserved remains of plants and animals. Fossils are rare in igneous rocks due to the high temperatures involved in their formation.
- The volcanic rocks formed at the surface have smaller mineral grains compared to those at depth:
This statement is correct. Volcanic rocks formed at the surface cool relatively quickly, resulting in smaller mineral grains. In contrast, rocks formed at greater depths have more time to cool, leading to larger mineral grains.
- Lithification is an important process of forming metamorphic rocks:
This statement is incorrect. Lithification is actually a process involved in the formation of sedimentary rocks, not metamorphic rocks. Metamorphic rocks are formed through the recrystallization of existing rocks under high pressure and temperature conditions.
Therefore, the correct statement among the given options is "2 only," as the other statements are either partially or completely incorrect.
Consider the following statements: Fossils are primarily found in ...
Based on the mode of formation three major groups of rocks are defined: Igneous, Sedimentary, and Metamorphic.
- Igneous rocks: Rocks formed out of solidification of magma (molten rock below the surface) and lava (molten rock above the surface) are known as igneous rocks. The igneous rocks are unfossiliferous as they form under conditions of high temperatures. Hence statement 1 is not correct. Igneous rocks are classified based on texture. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Hence statement 2 is correct.
- Sedimentary rocks: Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into sedimentary rocks. This process is called lithification. Hence statement 3 is not correct.
- Metamorphic rocks: When rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks, metamorphosis occurs. In the process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement is called foliation or lineation.
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