3. Reading comprehension

Informative reading: How continents evolve

You will read a passage, followed by questions about it. For each question, you need to select the one best answer A, B, C, or D to each question. Answer all the questions following the passage on the basis of what is stated/implied in the passage (R.P – 8.2.2, 8.2.4, 8.2.5, 8.2.6 )

Close study of the rocks of continents reveals ancient cores with progressively younger rocks tacked on to their rims. Each core, or craton, originated as a microcontinent, possibly like this. Two converging, cooling, horizontal currents in the mantle tugged on a tract of thin, early crustal rock then sank.

⁵This squashed and thickened that patch of crust. Its base bulged down and melted, releasing light material that punched up through the crust above. Such rock resorting could have formed the first small slabs of continental crust. Later, sea-floor spreading swept island arcs and sediments against microcontinents as mobile belts – belts of deformed and buckled rock. Accretion of this kind formed full-blown continents.

¹⁰About 5% of today’s continental crust had formed by 3.5 billion years ago, half by 2.5 billion years ago, most by 0.5 billion years ago. Once formed, continents are not immutable – they can be reworked, but not destroyed. Coalescing produced the supercontinent Pangea about 300 million years ago. Rifting later broke it up. Earth’s crust splits open above “hot spots” – fixed plumes of molten rock rising in the mantle.

¹⁵A plume formed the volcanic Hawaiian Islands by punching through the thin oceanic Pacific Plate passing over it. Plumes raise domes in the thick, rigid continental crust. A dome is liable to split in three as cracks grow outward from its top. Where three cracks widen, oceanic rock wells up into the spreading gaps.

²⁰The continent is split apart and a triple junction then separates three lithospheric plates. If spreading happens only in two cracks, two plates form. The third crack becomes an abandoned trough or rift. Nigera’s Benue Trough and Ethiopia’s Afar Depression are two such so-called aulacogens.

(Lambert “The Field Guide to Geology” 1988, Cambridge University Press)

1. What is the main purpose of the passage?

1. to show how first slabs formed the continental crust

2. to show how continents evolved

3. to show how the Earth’s crust split

4. to show how mobile belts deformed

2. Where in the passage does the author state how the continental crust was formed?

1. Lines 3-7

2. Lines 10-14

3. Lines 7-11

4. Lines 18-22

3. It can be inferred from the passage that the phrase “hot spots” refers to:

1. ash flow

2. lava flow

3. cooled magma

4. molten rocks

4. According to the passage, today’s continental crust was formed

1. 2.5 billion years ago

2. 0.5 billion years ago

3. 3.5 billion years ago

4. 300 billion years ago

5. According to the passage, full-blown continents were formed by

1. accretion

2. depression

3. subduction

4. separation

6. The author of the passage implies that the formed continents are

1. stable

2. progressive

3. spreading

4. immutable

7. What was the necessary conditions for the formation of Pangea?

1. resorting

2. subducting

3. coalescing

4. converging

8. According to the passage, plumes

1. raise domes in the continental crust

2. push molten rocks in the mantle

3. split the continent apart

4. deform the rocks