Previous Year Question
Which of the following are the evidences of the phenomenon of continental drift?
I. The belt of ancient rocks from Brazil coast matches with those from Western Africa.
II. The gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side.
III. The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere.
Select the correct answer using the codes given below.
Correct Answer: C
Detailed Solution
According to the continental-drift theory, the present continents were once parts of a united, much larger landmass. All three statements constitute geological evidence supporting this idea.
Statement I is correct:
A belt of approximately 2,000-million-year-old rocks along the Brazilian coast matches rocks of the same age in western Africa.
Similarities in the age, structure and sequence of rocks on opposite sides of the Atlantic indicate that South America and Africa were once joined.
Statement II is correct:
Rich placer deposits of gold occur along the coast of Ghana, although the source rocks for the gold are absent from that region.
Gold-bearing veins occur in the Brazilian plateau. It was therefore inferred that Ghana’s gold deposits were derived from the Brazilian plateau when South America and Africa lay side by side.
Statement III is correct:
Counterparts of India’s Gondwana sedimentary system occur in other Southern Hemisphere landmasses—Africa, the Falkland Islands, Madagascar, Antarctica and Australia.
Thick tillite at the base of these deposits provides evidence of extensive and prolonged glaciation.
Similar sedimentary sequences and palaeoclimatic evidence indicate that these landmasses were once parts of Gondwanaland.
Thus, all three statements provide evidence of continental drift.