Consider the following statements: 1. Rocks do not remain in their original form for long and undergo transformation. 2. Transformation of rocks is caused by weathering, erosion and metamorphic action. Which of the statements given above is/are correct?
- (a)1 only
- (b)2 only
- (c)Both 1 and 2
- (d)Neither 1 nor 2
Correct — C, Both 1 and 2. Both statements are correct. Rocks do not stay in their original form indefinitely — over geological time they are constantly transformed (statement 1) — and this transformation is brought about by weathering, erosion and metamorphic action (statement 2). Together these describe the rock cycle, in which igneous, sedimentary and metamorphic rocks continually change from one type into another.
- (a)1 only — Statement 2 is also correct: weathering, erosion and metamorphism are exactly the agents that transform rocks, so it cannot be '1 only'.
- (b)2 only — Statement 1 is also correct: rocks genuinely do not remain unchanged over geological time, so it cannot be '2 only'.
- (d)Neither 1 nor 2 — Both statements are true and, in fact, complementary, so 'neither' is wrong.
The rock cycle describes how the three rock families interconvert. Surface rocks are broken down by weathering and carried away by erosion to form sediments (and then sedimentary rocks); heat and pressure at depth cause metamorphism; melting and cooling produce igneous rocks. Thus no rock is permanent.
Both statements are individually true and reinforce each other — statement 2 simply names the mechanisms of the change asserted in statement 1. Recognising them as parts of the rock cycle gives 'Both 1 and 2'.
- The rock cycle links igneous, sedimentary and metamorphic rocks through continuous transformation.
- Weathering breaks rock in place; erosion removes and transports the debris.
- Metamorphism changes existing rock through heat and pressure without melting it.
- Melting and solidification form igneous rocks, completing the cycle.
- Existing rock exposed at the surface
- Weathering breaks it down; erosion removes and transports the debris
- Deposition and burial form sedimentary rock; heat and pressure cause metamorphism
- Melting and cooling form igneous rock — and the cycle repeats
Weathering, erosion and metamorphism continually transform rocks — both statements are correct, option (c).
- Assuming rocks are permanent — over geological time they are continually transformed.
- Reading the two statements as competing when statement 2 explains the mechanism of statement 1.
Two linked statements about rocks changing form — both are correct (the rock cycle).
Consider the following statements made about the sedimentary rocks: I. Sedimentary rocks are formed at Earth’s surface by the hydrological system. II. The formation of sedimentary rocks involves the weathering of pre-existing rocks. III. Sedimentary rocks contain fossils. IV. Sedimentary rocks typically occur in layers. Which of these statements are correct?
- (a) I and II
- (b) I and IV
- (c) II, III and IV
- (d) I, II, III and IV
Answer(d) I, II, III and IV
Same concept — the rock cycle. That item shows sedimentary rocks forming by weathering and erosion of pre-existing rock; this one asserts that rocks are continually transformed by those very processes.
Which one among the following processes is NOT part of chemical weathering?
- (a) Solution
- (b) Hydration
- (c) Reduction
- (d) Thawing
Answer(d) Thawing
Same area — weathering as an agent of rock transformation. That item distinguishes chemical-weathering processes; this one names weathering (with erosion and metamorphism) as what transforms rocks.
- practice — not a real PYQ
The continuous process by which one rock type changes into another is called the
- (a)nitrogen cycle
- (b)rock cycle
- (c)carbon cycle
- (d)water cycle
Answer(b) rock cycle — the interconversion of igneous, sedimentary and metamorphic rocks.
- practice — not a real PYQ
Which process changes an existing rock through heat and pressure without melting it?
- (a)Weathering
- (b)Erosion
- (c)Metamorphism
- (d)Deposition
Answer(c) Metamorphism — heat and pressure recrystallise the rock in the solid state.