Đề kiểm tra chất lượng ôn thi THPT Quốc gia môn Tiếng Anh Lớp 12 - Năm học 2017-2018 - Đề số 170

SỞ GD&ĐT VĨNH PHÚC
TRƯỜNG THPT LIỄN SƠN
(Đề thi gồm: 05 trang)
ĐỀ KTCL ÔN THI THPT QUỐC GIA NĂM 2017-2018
Môn: TIẾNG ANH – ĐỀ SỐ 170
Thời gian làm bài: 60 phút, không kể thời gian phát đề
Họ và tên thí sinh:. SBD:
Mark the letter A, B, C, or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions. 
Question 1:
A. chamber
B. ancient
C. danger
D. ancestor
Question 2:
A. smoothly
B. southern
C. breath
D. airworthy
Mark the letter A, B, C, or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in each of the following questions.
Question 3:
A. operation
B. supervision
C. reinforce
D. committee
Question 4:
A. overlook
B. influential
C. furniture
D. oceanic
Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
Question 5: The skin receives nearly the third of the blood pumped out by the heart.
	A. nearly 	B. the 	C. pumped out 	D. by 
Question 6: Salt was once too scare and precious that it was used as money. 
	A. once 	B. too 	C. and 	D. as money
Question 7: There being no evidence against himself, Slade was released. 
	A. There being 	B. no evidence 	C. himself 	D. was released
Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions.
Question 8: Are there any household chores for________ men are better________ than women?
	A. whose/suited	B. which/suit	C. that/suit	D. which/suited
Question 9: Too many factories dispose________ their waste by pumping it into rivers and the sea.
	A. out	B. of	C. away	D. off
Question 10: Why did Berth ask you________ a bicycle?
	A. that if you had	B. do you have	C. that you had	D. if you had
Question 11: She wondered if they________ her jeweler and rather hoped that they had.
	A. find	B. have found 	C. had found 	D. would find
Question 12: I cannot bear the noise of my brother’s radio; it________ me from my work.
	A. distracts	B. perturbs	C. interrupts	D. disturbs
Question 13: -“Is swimming under water very difficult?” 
-“No, it’s just a matter________ able to control your breathing.”
	A. to be	B. of being	C. that you are 	D. being
Question 14: I am going to the dentist’s tomorrow. I hope I don’t need to________.
	A. have anything done B. have nothing done	C. be done anything 	D. get him do anything
Question 15: A young girl came on to the stage with a bouquet________ to the conductor.
	A. Presented	B. and presented	C. for presenting	D. to present
Question 16: ________ I love you, I can’t let you do whatever you like.
	A. Whatever	B. Whether	C. Despite	D. Much as
Question 17: He________ alone a month ago, and________ of since.
	A. set off/hasn’t been heard 	B. setted off/hasn’t heard
	C. set on/hasn’t heard	D. setted on/hadn’t been heard 
Question 18: His________ of the school regulations really can’t be ignored any longer.
	A. carelessness	B. inattention	C. unfamiliarity	D. disregard
Question 19: Beaches were________ as police searched for canisters of toxic waste from the damaged ship.
	A. sealed off	B. cut off	C. washed up	D. kept out
Mark the letter A, B, C, or D on your answer sheet to indicate the most suitable response to complete each of the following exchanges.
Question 20: - Peter: “________________” 	- Tim: “What happened?”
	A. What did you do today? B. I had a bad day. C. How was your day? D. Have a nice day.
Question 21: Nancy: “Don’t fail to look after yourself, Mary!” – Mary: “_________________”
	A. Of course, you’re an adult. 	B. Oh, I knew about that.
	C. Thanks, me too. 	D. Thanks, I will. 
Mark the letter A, B, C, or D to indicate the phrase that is CLOSEST in meaning to the underlined ones.
Question 22: When you cross the street, be careful and be on the alert for the bus.
	A. Look for	B. watch out for	C. search for 	D. watch for
Question 23: He was asked to account for his presence at the scene of crime
	A. complain	B. exchange	C. explain	D. arrange
Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.
Question 24: In remote communities, it’s important to replenish stocks before the winter sets in.
	A. remake	B. empty	C. refill	D. repeat
Question 25: There has been no discernible improvement in the noise levels since lorries were banned.
	A. clear	B. obvious	C. thin	D. insignificant
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.
Question 26: Were it not for the money, this job wouldn’t be worthwhile.
	A. This job is not rewarding at all. C. Although the salary is poor, the job is worthwhile.
	B. This job offers a poor salary. D. The only thing that makes this job worthwhile is the money.
Question 27: At no time did the two sides look likely to reach an agreement
	A. The two sides had no time to reach an agreement. 
	B. The two sides never looked likely to reach an agreement.
	C. If the two sides had had time, they would have reached an agreement. 
	D. The two sides never look like each other.
Question 28: No matter how hard Fred tried to start the car, he didn’t succeed.
	A. Fred tried very hard to start the car, and succeeded.
	B. However hard Fred tried, he couldn’t start the car.
	C. It’s hard for Fred to start the car because he never succeeded. 
	D. Fred tried hard to start the car, and with success.
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
Question 29: The new restaurant looks good. However, it seems to have few customers
	A. In order to get more business, the new restaurant should improve its appearance.
	B. The new restaurant would have more customers if it looked better.
	C. If it had a few more customers, the new restaurant would look better. 
	D. In spite of its appearance, the new restaurant does not appear to attract much business.
Question 30: No one but the experts was able to realize that the painting was an imitation. It greatly resembled the original.
	A. It was obvious that only a person with great talent could fake a painting so successfully.
	B. It was almost impossible for amateurs to realize that the painting was not authentic, though the experts could judge it quite easily.
	C. The painting looked so much like the authentic one that only the experts could tell it wasn’t genuine.
	D. It was hard for ordinary people to judge between the fake painting and the real one.
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.
There has been an outbreak of avian influenza, better known as bird flu in Asia recently. The first (31)_______ died two weeks ago in Vietnam and there have been the cases reported since in Thailand, and there are some suspected cases in Cambodia as well as. 
 	Wild birds are affected by a large number of flu viruses, just as the humans and other animals are, but they are normally exclusive to birds. If the viruses manage to mutate, they can to jump the species barrier and infect human beings. The first case (32)_______ someone died was in Hong Kong in 1997. 
 	There are the several different forms of bird flu, ranging from mild to very (33)_______ infections, which spreading rapidly and kill many of the birds they infect. It is spread by wild birds-ducks, in particular – which carry the virus, but aren't killed by it. They can spread the virus to farm birds through (34)_______ contact or by the contaminating water supplies. 
World Health Organization officials have attributed the spread of bird flu to human contact with the droppings of infected birds and (35)_______ sanitation. There was no evidence at first that the virus spread from person to person, though there has been a case of this happening being investigated by scientists.
Question 31:
A. victim
B. casualty
C. sufferer
D. infector
Question 32:
A. where
B. when
C. which
D. why
Question 33:
A. strict
B. severe
C. serious
D. heavy
Question 34:
A. direct
B. straight
C. immediate
D. square
Question 35:
A. awful
B. bad
C. terrible
D. poor
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42. 
DESERTIFICATION
Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world. 
It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive droughts and recover, even in arid regions. Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practiced. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity leads to land abuse in these fragile marginal areas, soil destruction is inevitable. 
[1] Agriculture and overgrazing are the two major sources of desertification. [2] Large-scale farming requires extensive irrigation, which ultimately destroys lands by depleting its nutrients and leaching minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and 
erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature. 
Salination is a type of land degradation that involves an increase in the salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris- Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was in evident decline. In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later, vast tracks of salinized land between the Tigris and Euphrates rivers still resemble rock-hard fields of snow. 
Soil erosion is another form of desertification. It is a self-reinforcing process; once the cycle of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and run off is increased, floods become more frequent and more severe. Flooding washes away topsoil, the thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity occurs. Without this fragile coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert and the tropical African rain forests; home to some 56 million people. Overpopulation and overgrazing have opened the hyper-arid land to wind erosion, which is stripping away the protective margin of the Sahel, and causing the desert to grow at an alarming rate. Between 1950 and 1975, the Sahara Desert spread 100 kilometers southward through the Sahel. 
Question 36: Which of the following statement is true about desertification?
	A. It has a history as long as that of civilization. C. It is a fairy recent problem.
	B. It was just as serious in the past as it is today. D. Ancient societies managed the problem well.
Question 37: The word “arable” in paragraph 2 is closet in meaning to_______.
	A. cultivate	B. dry	C. settled	D. populated
Question 38: According to the passage, many people’s understanding of desertification is incorrect because_______.
	A. they do not think of it as a serious problem B. they see it as being reversible
	C. they do not see it as being caused by human activity D. they think of it as a very slow process
Question 39: According to the passage, agriculture furthers desertification through which of the following activities_______.
	A. The repetitive planting of the same crop	B. Irrigation
	C. The stripping away of native vegetation	D. Over fertilization
Question 40: The word “degradation” in paragraph 4 is closet in meaning to_______.
	A. rejuvenation	B. deterioration	C. contribution	D. consumption
Question 41: Paragraph 4 of the passage serves mainly to do which of the following?
	A. Show the progress of desertification down through history.
	B. Propose a method for dealing with the desertification problem.
	C. Describe one progress that leads to desertification. 
	D. Describe the main cause of desertification in one particular area. 
Question 42: The word “leaching” in paragraph 5 is closet in meaning to_______.
	A. washing	B. depositing	C. concentrating	D. dispersing
Read the following passage on transport, and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 43 to 50.
(1) Iron production was revolutionized in the early eighteenth century when coke was first used instead of charcoal for refining iron ore. Previously the poor quality of the iron had restricted its use in architecture to items such as chains and tie bars for supporting arches, vaults, and walls. With the improvement in refining ore, it was now possible to make cast-iron beams, columns, and girders. During the nineteenth century further advances were made, notably Bessemer’s process for converting iron into steel, which made the material more commercially viable.
(2) Iron was rapidly adopted for the construction of bridges, because its strength was far greater than that of stone or timber, but its use in the architecture of buildings developed more slowly. By 1800 a complete internal iron skeleton for buildings had been developed in industrial architecture replacing traditional timber beams, but it generally remained concealed. Apart from its low cost, the appeal of iron as a building material lay in its strength, its resistance to fire, and its potential to span vast areas. As a result, iron became increasingly popular as a structural material for more traditional styles of architecture during the nineteenth century, but it was invariably concealed.
(3) Significantly, the use of exposed iron occurred mainly in the new building types spawned by the Industrial Revolution: in factories, warehouses, commercial offices, exhibition hall, and railroad stations, where its practical advantages far outweighed its lack of status. Designers of the railroad stations of the new age explored the potential of iron, covering huge areas with spans that surpassed the great vaults of medieval churches and cathedrals. Paxton’s Crystal Palace, designed to house the Great Exhibition of 1851, covered an area of 1.848 feet by 408 feet in prefabricated units of glass set in iron frames. The Paris Exhibition of 1889 included both the widest span and the greatest height achieved so far with the Halle Des Machines, spanning 362 feet, and the Eiffel Tower 1,000 feet high. However, these achievements were mocked by the artistic elite of Paris as expensive and ugly follies. Iron, despite its structural advantages, had little aesthetic status. The use of an exposed iron structure in the more traditional styles of architecture was slower to develop.
Question 43: What does the passage mainly discuss?
	A. Advances in iron processing in the eighteenth and nineteenth centuries.
	B. The effects of the Industrial Revolution on traditional architectural styles.
	C. Advantages of stone and timber over steel as a building material.
	D. The evolution of the use of iron in architecture during the 1800’s.
Question 44: According to the passage, iron was NOT used for beams, columns, and girders prior to the early eighteenth century because_______.
	A. all available iron was needed for other purposes
	B. limited mining capability made iron too expensive
	C. iron was considered too valuable for use in public buildings
	D. the use of charcoal for refining ore produced poor quality iron
Question 45: Iron replaced stone and timber in the building of bridges because iron was considered_______.
	A. more beautiful	B. new and modern C. much stronger	D. easier to transport
Question 46: The word “it” in paragraph 2 refers to_______.
	A. industrial architecture	B. internal iron skeleton 
	C. stone	D. strength
Question 47: The word “surpassed” is closest in meaning to_______.
	A. imitated	B. exceeded	C. approached	D. included
Question 48: According to paragraph 3, the architectural significance of the Halle Des Machines was its _____.
	A. wide span	B. great height 
	C. unequaled beauty 	D. prefabricated unites of glass 
Question 49: How did the artistic elite mentioned in the passage react to the buildings at the Paris Exhibition?
	A. They tried to copy them.	B. They ridiculed them.
	C. They praised them. 	D. They refused to pay to see them.
Question 50: It can be inferred that the delayed use of exposed iron structures in traditional styles of architecture is best explained by the_______.
	A. impracticality of using iron for small, noncommercial buildings
	B. association of iron architecture with the problems of the Industrial Revolution
	C. general belief that iron offered less resistance to fire and harsh weather than traditional materials
	D. general perception that iron structures were not aesthetically pleasing
________HẾT_________
SỞ GD&ĐT VĨNH PHÚC
TRƯỜNG THPT LIỄN SƠN
(Đề thi gồm: 05 trang)
ĐỀ KTCL ÔN THI THPT QUỐC GIA NĂM 2017-2018
Môn: TIẾNG ANH – ĐỀ SỐ 170
Thời gian làm bài: 60 phút, không kể thời gian phát đề
Họ và tên thí sinh:. SBD:
Mark the letter A, B, C, or D on your answer sheet to indicate the word whose underlined part differs from the other three in pronunciation in each of the following questions. 
Question 1:
A. chamber
B. ancient
C. danger
D. ancestor
Question 2:
A. smoothly
B. southern
C. breath
D. airworthy
Mark the letter A, B, C, or D on your answer sheet to indicate the word that differs from the other three in the position of primary stress in each of the following questions.
Question 3:
A. operation
B. supervision
C. reinforce
D. committee
Question 4:
A. overlook
B. influential
C. furniture
D. oceanic
Mark the letter A, B, C or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.
Question 5: The skin receives nearly the third of the blood pumped out by the heart.
	A. nearly 	B. the 	C. pumped out 	D. by 
Question 6: Salt was once too scare and precious that it was used as money. 
	A. once 	B. too 	C. and 	D. as money
Question 7: There being no evidence against himself, Slade was released. 
	A. There being 	B. no evidence 	C. himself 	D. was released
Mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions.
Question 8: Are there any household chores for________ men are better________ than women?
	A. whose/suited	B. which/suit	C. that/suit	D. which/suited
Question 9: Too many factories dispose________ their waste by pumping it into rivers and the sea.
	A. out	B. of	C. away	D. off
Question 10: Why did Berth ask you________ a bicycle?
	A. that if you had	B. do you have	C. that you had	D. if you had
Question 11: She wondered if they________ her jeweler and rather hoped that they had.
	A. find	B. have found 	C. had found 	D. would find
Question 12: I cannot bear the noise of my brother’s radio; it________ me from my work.
	A. distracts	B. perturbs	C. interrupts	D. disturbs
Question 13: -“Is swimming under water very difficult?” 
-“No, it’s just a matter________ able to control your breathing.”
	A. to be	B. of being	C. that you are 	D. being
Question 14: I am going to the dentist’s tomorrow. I hope I don’t need to________.
	A. have anything done B. have nothing done	C. be done anything 	D. get him do anything
Question 15: A young girl came on to the stage with a bouquet________ to the conductor.
	A. Presented	B. and presented	C. for presenting	D. to present
Question 16: ________ I love you, I can’t let you do whatever you like.
	A. Whatever	B. Whether	C. Despite	D. Much as
Question 17: He________ alone a month ago, and________ of since.
	A. set off/hasn’t been heard 	B. setted off/hasn’t heard
	C. set on/hasn’t heard	D. setted on/hadn’t been heard 
Question 18: His________ of the school regulations really can’t be ignored any longer.
	A. carelessness	B. inattention	C. unfamiliarity	D. disregard
Question 19: Beaches were________ as police searched for canisters of toxic waste from the damaged ship.
	A. sealed off	B. cut off	C. washed up	D. kept out
Mark the letter A, B, C, or D on your answer sheet to indicate the most suitable response to complete each of the following exchanges.
Question 20: - Peter: “________________” 	- Tim: “What happened?”
	A. What did you do today? B. I had a bad day. C. How was your day? D. Have a nice day.
Question 21: Nancy: “Don’t fail to look after yourself, Mary!” – Mary: “_________________”
	A. Of course, you’re an adult. 	B. Oh, I knew about that.
	C. Thanks, me too. 	D. Thanks, I will. 
Mark the letter A, B, C, or D to indicate the phrase that is CLOSEST in meaning to the underlined ones.
Question 22: When you cross the street, be careful and be on the alert for the bus.
	A. Look for	B. watch out for	C. search for 	D. watch for
Question 23: He was asked to account for his presence at the scene of crime
	A. complain	B. exchange	C. explain	D. arrange
Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.
Question 24: In remote communities, it’s important to replenish stocks before the winter sets in.
	A. remake	B. empty	C. refill	D. repeat
Question 25: There has been no discernible improvement in the noise levels since lorries were banned.
	A. clear	B. obvious	C. thin	D. insignificant
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.
Question 26: Were it not for the money, this job wouldn’t be worthwhile.
	A. This job is not rewarding at all. C. Although the salary is poor, the job is worthwhile.
	B. This job offers a poor salary. D. The only thing that makes this job worthwhile is the money.
Question 27: At no time did the two sides look likely to reach an agreement
	A. The two sides had no time to reach an agreement. 
	B. The two sides never looked likely to reach an agreement.
	C. If the two sides had had time, they would have reached an agreement. 
	D. The two sides never look like each other.
Question 28: No matter how hard Fred tried to start the car, he didn’t succeed.
	A. Fred tried very hard to start the car, and succeeded.
	B. However hard Fred tried, he couldn’t start the car.
	C. It’s hard for Fred to start the car because he never succeeded. 
	D. Fred tried hard to start the car, and with success.
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.
Question 29: The new restaurant looks good. However, it seems to have few customers
	A. In order to get more business, the new restaurant should improve its appearance.
	B. The new restaurant would have more customers if it looked better.
	C. If it had a few more customers, the new restaurant would look better. 
	D. In spite of its appearance, the new restaurant does not appear to attract much business.
Question 30: No one but the experts was able to realize that the painting was an imitation. It greatly resembled the original.
	A. It was obvious that only a person with great talent could fake a painting so successfully.
	B. It was almost impossible for amateurs to realize that the painting was not authentic, though the experts could judge it quite easily.
	C. The painting looked so much like the authentic one that only the experts could tell it wasn’t genuine.
	D. It was hard for ordinary people to judge between the fake painting and the real one.
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.
There has been an outbreak of avian influenza, better known as bird flu in Asia recently. The first (31)_______ died two weeks ago in Vietnam and there have been the cases reported since in Thailand, and there are some suspected cases in Cambodia as well as. 
 	Wild birds are affected by a large number of flu viruses, just as the humans and other animals are, but they are normally exclusive to birds. If the viruses manage to mutate, they can to jump the species barrier and infect human beings. The first case (32)_______ someone died was in Hong Kong in 1997. 
 	There are the several different forms of bird flu, ranging from mild to very (33)_______ infections, which spreading rapidly and kill many of the birds they infect. It is spread by wild birds-ducks, in particular – which carry the virus, but aren't killed by it. They can spread the virus to farm birds through (34)_______ contact or by the contaminating water supplies. 
World Health Organization officials have attributed the spread of bird flu to human contact with the droppings of infected birds and (35)_______ sanitation. There was no evidence at first that the virus spread from person to person, though there has been a case of this happening being investigated by scientists.
Question 31:
A. victim
B. casualty
C. sufferer
D. infector
Question 32:
A. where
B. when
C. which
D. why
Question 33:
A. strict
B. severe
C. serious
D. heavy
Question 34:
A. direct
B. straight
C. immediate
D. square
Question 35:
A. awful
B. bad
C. terrible
D. poor
Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42. 
DESERTIFICATION
Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world. 
It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive droughts and recover, even in arid regions. Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practiced. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity leads to land abuse in these fragile marginal areas, soil destruction is inevitable. 
[1] Agriculture and overgrazing are the two major sources of desertification. [2] Large-scale farming requires extensive irrigation, which ultimately destroys lands by depleting its nutrients and leaching minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and 
erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature. 
Salination is a type of land degradation that involves an increase in the salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris- Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was in evident decline. In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian docum