We know very little about the materials of the whole lithosphere through direct observation. It is true that man has studied very intensively the rocks and minerals which are available to him, but these constitute only a small fraction of all the materials of the earth. Scientists have secured specimens from the slopes of Mount Everest at an elevation of more than 27,000 feet which prove that the mountain was once beneath the sea. One can study the materials on the walls of the great canyon or the deepest mines in the world. Several well borings for oil have reached depths of from 12,000 to more than 15,000 feet, and through examination of the drill cuttings, one can determine the nature of the rocks at any depth in the hole. However, all rock exposures so far available to man are small compared with the 4,000-mile radius of the earth.
The word lithosphere really means rock sphere. Rocks, then, constitute most of the solid material of the earth. One can divide rocks into three great groups: igneous, rocks, sedimentary rocks and metamorphic rocks. Nearly all rocks contain two or more minerals.
Igneous rocks. Igneous rocks are those resulting from the interior heat of the earth. There are two main kinds: 1) those which reach the surface in volcanoes, 2) and those which moved underground but became solid before they reached the surface.
Sedimentary rocks. During the long periods of geologic time, igneous rocks have undergone erosion. The forces of erosion carried away particles of eroded rock and set them down in layers either on dry land or under water. As a result, this material changed into another type of solid material known as sedimentary rock.
Metamorphic rocks. As a result of heat, pressure and movement, igneous and sedimentary rocks changed their original qualities in some way forming a new material called metamorphic rocks. The metamorphic rocks are generally crystalline and harder than the original material.
Notes
as a result of smth. -
so far
WORDS
observation
true , ,
intensive
mineral ,
available ( )
to constitute
fraction , ,
to secure , ,
specimen ,
canyon ,
mine
well boring
oil
to reach
drill cutting ( )
to determine
nature ,
hole ,
exposure
to compare
radius
igneous
sedimentary
to result from , ,
volcano
geologic
to undergo ,
to erode ,
erosion
original
quality
crystalline ,
I. Answer the following questions:
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1. How do we learn things about lithosphere?
2. Where do scientists secure specimens?
3. What do specimens from the slopes of Mount Everest prove?
4. What depths have several well borings reached?
5. How can you determine the nature of the rocks?
6. Why can't we learn much about lithosphere through direct observation?
7. What do rocks constitute?
8. Into what large groups can we divide rocks?
9. What do all rocks contain?
10.What is the nature of igneous rocks?
11. What kinds of igneous rocks do you know?
12. How many active volcanoes do you know?
13. Are there any active volcanoes in our country?
14. What processes do igneous rocks undergo?
15. What happens to particles of eroded rocks?
16. Under the influence of what forces do igneous and sedimentary rocks change their qualities?
17. What is the difference between igneous and metamorphic rocks?
II. Find in the text equivalents to:
to deposit, almost, at one time, to make up, some, height, under, over.
III. From questions to the italicized words:
1. Mountain climbers have reached elevations of 27 000 feet on Mount Everest.
2. The forces of erosion carried away particles of eroded rocks.
3. Igneous rocks constitute the great bulk of the lithosphere.
4. They will study the materials on the walls of deepest mines.
IV. Translate into Russian. Pay attention to the verb "to have":
They have specimens.
They have to secure specimens.
They have secured specimens.
1. Many of the most important changes have taken place on the surface of the earth.
2. The earth has a diameter of approximately 8 000 miles.
3. Scientists have to secure many specimens before they can determine the nature of the rock.
4. The surface of the earth has low relief.
5. For centuries men have secured salt from the ocean.
6. Ships go round the earth in an east and west direction, but it is also possible to go round in a north and south direction. But that is much more difficult because we have to pass the very cold Arctic regions and only a few brave men have been able to penetrate into the heart of those cold lands.
7. The earth has an outer shell 40 to 50 miles in thickness, beneath which there is a mass of iron of iron and nickel.
8. They had to examine many specimens before they could determine the nature of this rock.
PART II
SUPPLEMENTARY READING
