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Text 4. WANDERING CONTINENTS



Anyone who has looked at a world map must have noticed how snugly the coastline of Africa and the Americas could be made to fit together, if the intervening ocean were removed. Modern geophysics has established that all of the Earth's landmasses were indeed joined together in one supercontinent, Pangaea, hundreds of millions of years ago, and that this supercontinent was broken apart, with the land masses drifting to their present positions on the globe.

His idea took many years to become established. Speculations about the fit of the continents go back to Francis Bacon (1561-1626), but the acknowledged “father” of the idea of continental drift was the German astronomer and meteorologist Alfred Wegener, who published the first comprehensive statement of the theory in 1912. Wegener thought that the continents might move through the thinner crust of the ocean floor, like icebergs ploughing through the sea, and he gathered a wealth of evidence showing how well the continents could be fitted together like some global jigsaw puzzle. But the idea of continents moving through the rocks of the sea floor did not seem feasible, and found little favour until the 1950s, when the development of new geological techniques provided conclusive evidence that the continents do move.

The key evidence came from magnetic studies of the ocean floors. These showed that the crust of the Atlantic Ocean floor is arranged symmetrically on either side of a great ridge of volcanic activity which runs roughly down the center of the ocean bed. The interpretation of this discovery is that new oceanic crust is being created at the mid-ocean ridge, where it wells up through a crack in the Earth’s crust and is pushing out on either side, steadily widening the Atlantic.

In other parts of the world the reverse happens. The North Pacific, for example, has no oceanic ridge, but there is a deep trench running down the west of the ocean floor, next to the Eurasian landmass. There the thin crust of the ocean floor is being pushed under the continent, back down into the mantle where it melts and is ultimately recycled. The net effect is that there is no change in the surface area of the Earth — spreading in the Atlantic and at other sites is balanced by contraction of the Pacific. A piece of the Earth’s crust that is bounded by spreading ridges and subduction zones is called a “plate”, which gives the concept of continental drift its modern name, “plate tectonics”. In some places, two pieces of crust — two plates — rub side by side, with no net creation or destruction of sea floor. This happens today along the notorious San Andreas fault in California.

The whole process of break-up and re-arrangement of the continents may have happened several times in the Earth’s history, and is responsible for building mountain ranges, where continents collide. India, moving northward into Eurasia, has forced up the Himalayas, which are still growing. By contrast, the line of the Red Sea marks a new (by geological standards) crack in the Earth's crust, a spreading ridge which is splitting Africa off from Arabia, and which may eventually cause this narrow sea to expand into an ocean as large as the Atlantic is today.

Overwhelming evidence for the reality of continental drift, or plate tectonics, was collected during the 1960s and 1970s. But the "icing on the cake" has been provided only in the past few years. Using laser beams bounced off artificial satelites in orbit around the Earth, it is now possible to measure directly the steady widening of the Atlantic, calculated at a couple of centimetres every year.

 

From “The Courier”

 

I. Read the text ‘Wandering Continents’. Arrange the following sentences in a logical sequence corresponding to the contents of the text.

 

1. Magnetic studies of the ocean floors gave the key evidence of the continental drift.

2. Hundreds of millions of years ago all of the Earth’s landmasses were joined together in one supercontinent.

3. The net effect is that there is no change in the surface area of the Earth – spreading in the Atlantic and at other sites is balanced by contraction of the Pacific.

4. Thanks to laser beams, it is now possible to measure directly the steady widening of the Atlantic.

5. The idea of continental drift was stated by the German astronomer and meteorologist Alfred Wegener.

6. The process of re-arrangement of the continents is responsible for building mountain ranges, where continents collide.

7. New geological techniques supported the idea of continents moving through the rocks of the sea floor.

8. Plate tectonics is the modern name for the concept of continental drift.

 

II. Find the sentences with ing-forms. Define their functions.

 

III. Translate the text.

Text 5. OUR SOLAR FAMILY

Our solar family consists of the sun, nine known planets and their satellites, asteroids, comets and meteors.

The most important body in this great family is the sun. There are few kinds of energy on the earth that are not the gift of the sun.

The sun's mass is 750 times that of all the planets, put together. Like all the other bodies in the iniverse, it is composed of the same sort of materials we find on the earth. Of all the elements or building blocks of nature which we have discovered, some 68 have been found on the sun, and none have been found in the sun which are not now known on earth.

Our sun has a surface temperature of about 6,000°C. A star as hot as the sun must radiate an enormous amount of heat.

Every square metre of the sun's surface radiates energy equal to 84,000 horse power. Yet, the total amount the earth receives is only a very small fraction of it. Here is a possible source of energy for the future. The age of the earth is about two billions of years. The sun must have been in existence long before the earth was formed. During all that time the sun has been radiating heat continuously, and still continues to do so. To produce this great amount of heat would require the hourly burning over its entire surface of a layer of highgrade anthracite coal sixteen feet thick. If the heat of the sun were produced by burning coal, it would require an inexhaustible supply to furnish such intense heat over this great period of time.

 

THE PLANETS

Planets, the most important bodies of the sun's family, are of greatest interest to man, not simply because they are nearest to him, but because he lives, works, and enjoys life on one of them. If somewhere life similar to ours exists, we must look for it on planets, not on stars, comets, or meteors.

The sun has a family of nine planets moving around it in orbits that are ellipses, and not circles. Their names in order from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

The ancients recognized that these bodies did not remain fixed, but were constantly shifting their positions on the celestial sphere night after night and month after month; so they named them planets, which means "wanderers."

Mercury is not only the nearest planet to the sun, but it is, with one possible exception, the smallest of the planets. It is the swiftest in its movement about the sun, and its year consists of eighty-eight days. Because of the difficulty of locating it in the bright twilight, it has been called the "elusive planet. " Venus is the brightest star in the sky, next to the sun and the moon. When it appears as an evening or morning star, it shines very brightly. It is certain that the planet has an atmosphere, since it is constantly enveloped in clouds.

Of all the planets, the earth is the most important to us. It is literally beneath our feet, and we can study it scientifically in greatest detail. Although we live only upon its surface, it is possible to determine its shape, size, mass, motions, and their effects. This knowledge has been gradually accumulated.

Jupiter is the giant among the family of planets. It has a diameter 11 times that of the earth. Not only is Jupiter the largest planet, but it is whirling rather quickly, completing a rotation every 9 hours and 58 minutes. In its movement around the sun, however, it is rather slow, requiring almost 12 years to make a complete revolution.

Jupiter has a family of eleven satellites, and two of them are larger than Mercury. Beyond Jupiter is Saturn, the second largest of the planets. It has a family of nine satellites, one of which, Titan, is larger than our moon.

The most impressive thing about Saturn is its ring system. The rings lie like thin sheets of silver around the planet's equator. There are three of them.

Little is known of the planets Uranus, Neptune and Pluto, they are so far away that the most powerful telescope cannot reveal anything but small, illuminated bodies. Uranus and Neptune are small when contrasted with the earth. Uranus has four satellites and Neptune one; Pluto may not have any.

Because of the earth's rotation, we have day and night on the earth. Revolution is the earth's yearly motion about the sun. The path that the earth pursues is called its orbit. Although it is really an ellipse, it is so nearly round as to appear a true circle.

Mars aroused more interest than any of the other planets. When nearest the earth, as it was in September 1956, it is an object of great beauty.

There are many ways in which this planet is similar to the earth. It rotates on an axis in about the same time as does the earth. It has seasons similar to the seasons on the earth, except that they are nearly twice as long.

Small bodies located between the orbits of Mars and Jupiter are called asteroids.

Of these bodies, called "planetoids" or miniature planets, the largest is Ceres-780 kilometres in diameter. Their origin is, as yet, not fully known. It is thought that they represent small masses of matter that were not able to combine into larger ones during the genesis of the solar family.

 

I. Read the text ‘Our Solar Family’ without a dictionary. Try to understand it.

 

II. Find the key sentence in each paragraph of the text.

 

III. Make up the plan of the text ‘Our Solar Family’.

 

IV. Speak about our solar system. Use the plan you’ve made up.






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