Fig. 8 . Structure of the Earth

1 – inner core; 2 – convection currents; 3 – outer core; 4 – lower mantle; 5 – upper mantle; 6 – asthenosphere; 7 – lithosphere.

3. READING COMPREHENSION

3.1 INFORMATIVE READING - The Earth (R.P – 3.1, 3.2)

3.1.1.Read the text and for questions 1-10, choose the best answer: A, B, C or D. Then explain the words in bold.

The Earth’s structure is a reflection of its original accretion growth and subsequently physical and compositional evolution. The Earth consists of a series of concentric shells of different physical and chemical properties.

The globe is surrounded by a gaseous envelope consisting chiefly of nitrogen (78%) and oxygen (21%). The atmosphere is densest at sea level and becomes progressively upward. The lower zone, approximately 0-10km is the troposphere with the less dense stratosphere overlying.

The ocean basins make up approximately two-thirds of the surface of the solid Earth: they are great depressions lying average 5 km below sea level, while continents and islands, constitute one-third of the solid Earth’s surface.

The Earth’s surface consists mainly of ocean water, covering slightly more than 70% of the exposed area; land, some of which is lake-or ice-covered, constitutes the remainder. The outer rind of the solid Earth, or crust, is two distinctly different types. Continental crust, rich in silica, alkalis, volatiles and radioactive elements, is characterized by granitic rocks and is approximately 20-60 km thick. Ocean crust is almost exclusively basaltic in composition and is approximately 5km. thick. The crust is a very thin skin, representing a little less than 1% by volume of the whole Earth and only approximately 0.4% by mass.

The more or less horizontal boundary between the crust and the underlying mantle-both beneath the continents and ocean basins is known as the Mohorovicic Discontinuity (Moho / M). This discontinuity is a zone of finite thickness in which lower crust and upper mantle are interlayered.

The mantle represents the largest proportion of the Earth, some 83% by volume and 68% by mass. It is rich in magnesium and less rich in iron. It consists of a number of distinct but intergradational layers. The uppermost layer is relatively rigid and with the overlying rigid crust is called the lithosphere (or rocky surface). The lithosphere may be several hundred kilometers thick. The lithosphere (both mantle and crust) covers the entire planet and is divided into seven gigantic plates and numerous smaller ones. Beneath the lithosphere lies the more ductile mantle layer known as the asthenosphere (glassy or weak zone). The so-called upper mantle consists of lithosphere plus asthenosphere plus more rigid mantle material down to depths of approximately 300-400 km. The transition zone of the upper mantle is situated between the depths of 400-670 km. In this region the physical properties of the upper mantle change fairly and continuously with increasing depth. The gradual emergence of nearly constant physical characteristics below the transition zone signals passage into the lower mantle. This innermost and most voluminous mantle shell appears to be relatively homogeneous.

The core-mantle boundary and a thin basalt mantle (termed “D”) represent a layer of profound change in the constitution of the materials that makes up the Earth. The overlying mantle shells consist of magnesium and silicon oxide phases. The inner core appears to be a solid iron-nickel alloy. The outer core (molten) makes up approximately 15% of the Earth volume. The inner core constitutes the remaining 1% by volume of the planet. Because of its great density, the core represents more than 31% of the Earth’s mass. (Barret E., Hunt A. And Milner B.” Earth and Atmosphere”, 1993, Longman)

Fig. 9. Composition of the Earth’s crust.

1 – basalt, 2 – intrusion; 3 – mantle; 4 – crystalline rock; 5 – granite; 6 – sedimentary rock.

1. What does the Earth consist of?

A. shells

B. beds

C. layers

D. parts

2. The globe surrounded by a gaseous envelope is called

A. hydrosphere

B. asthenosphere

C. lithosphere

D. atmosphere

3. The atmosphere consists of

A. nitrogen and carbon

B. oxygen and nitrogen

C. carbon and oxygen

D. hydrogen and oxygen

4. The ocean basin makes up approximately __________ of the Earth.

A. one third

B. three fourths

C. two thirds

D. one fourth

5. One third of the Earth’s surface consists of

A. land and water

B. isles and islands

C. continents and mountains

D. continents and islands

6. Continental crust is of ___________ composition.

A. basaltic

B. granitic

C. dolomitic

D. limestone

7. Crust is composed of

A. skin

B. layer

C. shell

D. ball

8. Moho is a zone between

A. outer core and inner core

B. crust and atmosphere

C. mantle and outer core

D. crust and mantle

9. The mantle is rich in

A. iron

B. silica

C. magnesium

D. basalt

10. The asthenosphere is a

A. weak sphere

B. rigid sphere

C. ductile sphere

D. finite sphere

11. The lithosphere is divided into how many plates?

A. six

B. five

C. nine

D. seven

12. Where is the transition zone located?

A. above the upper mantle

B. above the lower mantle

C. near the lithosphere

D. above the core

13. What letter stands for the core-mantle boundary?

A. A

B. B

C. D

D. C

14. Why does the core represent 31% of the Earth’s mass?

A. density

B. gravity

C. weight

D. mass

3.1.2 Read the text once more and fill in the chart with the necessary information. Then label the diagram and give an explanation what each item means.

THE EARTH

Part	Division	Volume	Composition	Depth	Other terms

3.1.3. Using this diagram, answer the following questions as briefly as possible. Use the information from the text « The Earth » and describe the diagram. (Paul Nixon & Alferdo Bezzi “English for Geologists”)

1. Does the Moho separate the mantle and the crust?

2. Is the lithosphere topped by a relatively lightweight crust?

3. Does the crust vary in thickness?

4. Where is the crust thinnest?

5. Does the lithosphere include the uppermost part of the mantle and crust?

6. Is the asthenosphere rigid?

3.2 DETAILED READING - Earth’s size and shape

Read the text and then complete the task. Fill in the gaps.

Instruments including artificial satellites have helped scientists work out the Earth’s size, shape and other features. We know ours is one of the smallest, lightest planets of the solar system. Four others far exceed its mass and volume. But no planet has a greater density (5.5 times that of water).

Careful measurements prove the ball-like Earth is not in fact a sphere. It measures 24,901.5 mi. (40 074 km) around the equator, but only 24,859.7 mi. (40 008 km) around the poles. So our planet bugles slightly at the equator and is slightly flattened at the poles.

Centrifugal force created by the Earth’s spin produced this shape, an oblate spheroid. Even that description oversimplifies, for the Earth is very slightly pear-shaped.

Scientists accordingly use the term “geoid“ (earth shaped) to describe the Earth’s hypothetical, mean-sea-level surface-ignoring wrinkles formed by mountain chains and ocean floors. Geoid measurement involves taking sea-level gravity readings by gravimeter and studying “kinks” in orbits of artificial satellites. Both reveal so-called gravity anomalies reflecting local differences in mass in the Earth’s crust and mantle. Such differences account for vast but slight dips and bumps in the geoid’s surface.

Gravity anomalies also reinforce the theory of isostasy – a state of balance in the Earth’s crust where continents of light material float on a denser substance into which deep continental “roots” project like the underwater mass of floating icebergs.

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

Fill in the gaps using the words under the line

Artificial satellites have helped scientists to work out the Earth’s (1)__________ and shape. The Earth is the (2)__________ planet of the solar system. But it has a greater (3)__________ than all the other planets. Measurements prove that the Earth is not a (4)_________. Earth’s (5)_________ produced this shape- oblate spheroid. Scientists use the term (6)_________ to describe the Earth’s surface. It involves taking sea-level (7)_________ and studying (8) __________ in orbits. These reveal so-called (9)_________. They reflect the differences in the Earth’s (10)________ and mantle. Gravity anomalies reinforce the theory of (11)________. This term means the state of balance in the Earth’s (12)____________.

size density gravity lightest spin

kinks sphere geoid anomalies crust × (2)

isostasy

3.3 SCANNING- Earth’s building blocks

You are looking for specific information. Don’t read every word. Run your eye down the text and stop when you find the relevant (важный; существенный) words. You have 3-4 minutes.

1. building blocks-

2. abundance of elements-

3. elements-

4. silicate-

5. crystal-

6. mineral identification-

Earth’s building blocks are elements and minerals of our planet. Of 92 naturally occurring elements, eight account for 98% of the weight of the Earth’s crust – the rocky layer that scientists know best. Nearly 3/4 of its weight lies in two non-metals – oxygen and silicon; most of the rest consists of the six metals-aluminum, iron, calcium, sodium, potassium and magnesium.

Within the crust most elements occur as minerals- natural substances that differ chemically and have distinct atomic structures. The Earth’s crust holds about 2000 kinds of minerals. A few (including gold) occur as just one element; most comprise two or more elements chemically joined as compounds.

Silicates (minerals containing silicon and oxygen) are the most abundant minerals in crust and mantle, which make up 4/5 of our planet’s volume.

Most minerals formed from fluids that solidified – a process that arranged their atoms geometrically producing crystals. Scientists identify six crystal systems based on axes-imaginary lines passing through the middle of a crystal. Each system yields crystals with distinctive symmetry. Within each system, each mineral crystal grows in a special shape or habit, though this can be modified by temperature, pressure and impurities.

Traditional tests identify by hardness, color, streak (color of the powered mineral), luster, specific gravity, cleavage, fracture, form, tenacity (resistance to bending, breaking and other forces), odor, taste and feel.

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

Fig. 10 Relative abundance of elements in whole Earth

Fig. 11 Relative abundance of elements in Earth’s crust

4. LISTENING COMPREHENSION

You will hear a lecture. After the lecture you will hear some statements. The lecture and questions will be spoken just one time. When you hear a statement, read the three possible answers, and decide which one would be the best answer to the statement you have heard.

1. The crystal rind is covered by

A. condensed atmosphere components

B. volatile atmosphere components

C. ocean volatile components

2. The mantle lies under

A. oxide rich shells

B. rocky exterior

C. concentric shells

3. They are

A. constructing blocks

B. constructing rocks

C. constructing layers

4. The main factor is

A. sunlight only

B. the Earth itself

C. physicochemical evolution

5. The following systems

A. protection

B. interconnected

C. biological

4.2 You will hear part of a radio report about the earth as a planet of our solar system. For statements 6- 15, complete the notes that summarize what the speaker says. You will need to write a word or a short phrase in each box.

Earth is a
The Earth is the third planet to
The planets don’t fly into space because of
Life on Earth is due to
Each rotation produces
The Moon completes
while Earth completes
This is an Earth’s
The Earth is separated from the other bodies by
So, the solar system comprises

4.3. You will hear a lecture on the Earth’s origin. For statements 16-20, choose the best answer A, B, C, D.

16. Which of the following elements are the lightest?

A. hydrogen and oxygen

B. hydrogen and helium

C. helium and carbon

D. hydrogen and carbon

17. What is the meaning of «blob»?

A. dense spot

B. locked particle

C. abundant element

D. considering clouds

18. After burning helium, stars swell into

A. dwarfs

B. galaxies

C. giants

D. planets

19. What does the following passage describe?

A. how the Earth was created

B. how the “ big bang” changed the Earth

C. how immense explosions created new stars

D. how new stars created different elements

20. What would the author discuss in the following passage?

A. star factories

B. rare and common elements

C. the life of a star

D. how the Sun and planets were formed

5. DISCUSSION: (R.P – 3.1, 3.3)