The Surface of the Ground

Wherever we live we know that the surface of the land is not always the same. There are some places which are flat or level, there are some places which are hilly.

Even if we live in the middle of a big city we can tell this because the roads go slightly uphill. Perhaps many of us have never seen high mountains, which rise thousands of feet, but we can all imagine, at least partly, what they look like. It is not difficult to understand also how the surface of the country affects the life of man, for where there is flat land or gently rolling land, it is not difficult to build houses and so villages and towns arise. On flat land, too, we can easily construct railways and roads. But if you can imagine a land full of giant mountains it would be very difficult indeed to build houses on the mountain sides, and indeed there would be few reasons for building them there. It would not be possible to cultivate the fields round about, and so we find that mountainous areas usually have few people, or, as we say, are thinly inhabited, whilst flat lands or valley lands often have very many people indeed.

Ex. 6. Choose one of the following items and write an essay. Use additional material.

1. Three ways of the formation of islands.

2. The difference between mountains and hills.

3. The difference between a mountain and a plateau.

4. The four types of plains.

Text B

Task. Read the text end get ready to discuss its main points.

Continental Drift

A casual glance at a map of the world suggests the possibility that at some time in the past the continents were joined together in one or two giant supercontinents. If the margins of the continents are taken to be on their continental slopes at a depth of 3,000 ft, instead of their present sea-level boundaries, the fit between North and South America, Africa, Greenland, and western Europe is remarkably exact. But merely matching up outlines of continents is not by itself sufficient evidence that the continents have migrated around the globe. The first really comprehensive theory of continental drift was proposed early in this century by the German meteorologist Alfred Wegener, who based his argument on biologic and geologic evidence.

Wegener’s Theory

At one time the standard explanation for the similarity of patterns of early life around the world was a series of land bridges linking the continents together. But this meant that the oceans were then separated from one another, so a series of channels had to be devised to permit aquatic plants and animals to pass between the oceans. No really believable scheme of bridges and channels could be devised, and even if one had been, it would still be necessary to account for the disappearance of all traces of them. Wegener was on firm ground when he searched for an alternative to this notion.

What Wegener suggested instead was that originally the continents were all part of a huge landmass he called Pangaea that was surrounded by a single ocean, Panthalassa. Pangaea then began to break up and the continents to slowly drift to their present locations. This model found additional support in geological data regarding prehistoric climates. At one time, South Africa, India, Australia, and part of South America were burdened with great ice sheets, while at the same time a tropical rain forest covered North America, Europe, and China. At various other times, there was sufficient vegetation in Alaska and Antarctica for coal deposits to have resulted, and so currently frigid a place as Baffin Bay was a desert.

Wegener and his followers examined what was known about the climates of the distant past, and tried to arrange the continents in each geologic period so that the glaciers were near the poles and the hot regions were near the equator. The results, in general, were quite convincing, and in some cases startlingly so: deposits of glacial debris and fossil remains of certain distinctive plant species follow each other in the same succession in Argentina, Brazil, South Africa, Antarctica, India, and Australia, for example. A recent discovery of this kind was the identification of a skull of the reptile Lystrosaurus in a sandstone layer in the Alexandra mountain range of Antarctica. This creature, which was about three feet long, flourished long ago in Africa. It is as unlikely that Lystrosaurus swam the 2,700 mi between Africa and Antarctica as it is that a land bridge this long connected them, only to vanish completely later on.

Ex. 1. Here are the answers to some questions on the text. What are the questions?

1. At some time in the past the continents were joined together in one or to giant supercontinents. (In how many supercontinents?)

2. The first comprehensive theory of continental drift was proposed early in this century by the German meteorologist Alfred Wegener. (When? By whom?)

3. Alfred Wegener based his theory on biologic and geologic evidence. (On what?)

4. Wegener suggested that originally the continents were all part of a huge landmass that was surrounded by a single ocean. (What?)

5. At one time South Africa, India, Australia and part of South America were burdened with great ice sheets. (With what?).

6. Wegener and his followers examined what was known about the climates of the distant past. (What?).

7. Wegener tried to arrange the continents in each geologic period. (What?)

8. The results were quite convincing. (What?)

9. In some cases the results were startlingly so: deposits of glacial debris and fossil remains of certain distinctive plant species follow each other in the same succession in Argentina, Brazil, South Africa, Antarctica, India and Australia. (In what countries?).

Ex. 2. Complete the sentences.

1. A casual glance at a map of the world suggests … .

2. The fit between North and South America, Africa, Greenland and Western Europe is … .

3. Merely matching up outlines of continents is not sufficient evidence that … .

4. The standard explanation for similarity of patterns of early life around the world was … .

5. The oceans were then separated … .

6. Wegener called a huge landmass … .

7. Pangaea was surrounded by … .

8. Then Pangaea began to break up and continents began to … .

Ex. 3. Expand on the following:

1. The continents have migrated around the globe.

2. Wegener proposed the first really comprehensive theory of continental drift.

3. According to Wegener originally the continents were all part of a huge landmass.

4. The glaciers were near the poles and the hot regions were near the equator.

Ex. 4. Discuss the following.

1. Wegener suggestion.

2. The evidence for continental drift.

3. The weakness of Wegener’s idea.

4. The attitude of geologists to the idea of continental drift.

Text C

Task. Scan the text and say by what the separation of Pangaea into two supercontinents is supported. Explain why continental drift was not widely accepted until very recently.

Today it seems almost certain that Pangaea did exist and later began to break apart into two supercontinents, Laurasia (which consisted of what is now North America, Greenland, and most of Eurasia) and Gondwanaland (South America, Africa, Antarctica, India and Australia). Laurasia and Gondwanaland were almost equal in size. The separation of Pangaea into these supercontinents is supported by detailed geological and biological evidence, for instance certain differences between Laurasian and Gondwanaland fossils of the same age.

Laurasia and Gondwanaland were separated by a body of water called the Tethys Sea. Today a little of the Tethys Sea survives as the Mediterranean, Caspian, and Black Seas, but its original extent can be gauged from the sediments that were subsequently uplifted to form the mountain ranges that stretch from Gibraltar eastward to the Pacific. The Pyrenees, Alps, and Caucasus of Europe, the Atlas Mountains of North Africa, and the Himalayas of Asia all were once part of the Tethys Sea.

Not long after Pangaea split apart, South America and Africa became detached as a unit from the rest of Gondwanaland, and later they separated as the South Atlantic Ocean came into being. At a later date the Atlantic Ocean completed its extension northward, Australia separated from Antarctica, and India began to drift toward Asia.

The geologic processes responsible for continental drift are on such a huge scale that it is hard to believe they began relatively recently in the history of the earth. Hence it is likely that continental drift was taking place even before Pangaea was formed, and in fact there is some evidence that Pangaea was the result of the coming together of three earlier landmasses, Gondwanaland, Asia east of the Ural Mountains, and a unit consisting of North America, Greenland, and Europe.

Continental drift, then, has some very attractive aspects. Why was it not widely accepted until very recently? Wegener, who lacked a knowledge of the mechanical properties of the various parts of the earth's crust, envisioned the continents as floating freely over the mantle and having no trouble in moving through the ocean floors. If this were the case, only relatively weak forces would be needed to move the continents over the face of the earth, and Wegener was able to cite several such forces. But the ocean floors are in fact extremely hard and strong, and if enough force could somehow be applied, it seems likely that a continent would buckle rather than pass through the ocean floor.

An entirely different mechanism has proved to be involved, and until its discovery in the middle 1960s continental drift, for all its allure, remained discredited by most geologists.

Ex. 1. Put the sentences in logical order.

1. The Pyrenees, Alps and Caucasus of Europe, the Atlas Mountains of North Africa, and the Himalayas of Asia all were once part of the Tethys Sea.

2. Until its discovery in the middle 1960s continental drift remained discredited by the most geologists.

3. Pangaea did exist and later began to break apart into two supercontinents, Laurasia and Gondwanaland.

4. Later South America and Africa separated as the South Atlantic Ocean came into being.

5. It is likely that continental drift was taking place even before Pangaea was formed.

6. Laurasia and Gondwanaland were almost equal in size.

7. Today a little of the Tethys Sea survives as the Mediterranean, Caspian and Black Sea.

8. Laurasia and Gondwanaland were separated by a body of water called the Tethys Sea.

Ex. 2. Complete a chart below.

Names of two super­continents	The present name of the continents Laurasia consisted of	The present name of the continents Gondwanaland consisted of	The names of the mountains which were once part of the Tethys sea

Ex. 3. Discuss in groups the problems raised in the text.