托福阅读OG Desert Formation答案与解析

Desert Formation

1.

核心词汇总结

occupy

占据

approximately

大约

previously

以前

desertification

沙漠化

estimate

估计

vegetation

植被

typically

作为特色地

substantial

大量的

impact

影响，效果，撞击

particle

颗粒

seal

密封

penetration

渗透

absorption

吸收

consequently

因此，结果

erosion

侵蚀

diminish

减弱

deterioration

恶化

primarily

主要地

semiarid

半干旱的

delicate

脆弱的

devoid

缺乏的

salinization

盐碱化

evaporation

蒸发

millennia

千年

rigorously

严格地

2.

长难句总结

(1)

The extreme seriousness of desertification results from the vast areas of land and

the tremendous numbers of people affected, as well as from the great difficulty of

reversing or even slowing the process.

(2)

Even in the areas that retain a soil cover, the reduction of vegetation typically

results in the loss of the soil's ability to absorb substantial quantities of water.

(3)

The semiarid lands bordering the deserts exist in a delicate ecological balance and

are limited in their potential to adjust to increased environmental pressures.

(4)

During the dry periods that are common phenomena along the desert margins,

though, the pressure on the land is often far in excess of its diminished capacity, and

desertification results.

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(5)

The consequences of an excessive number of livestock grazing in an area are the

reduction of the vegetation cover and the trampling and pulverization of the soil.

P1

：

introduction

The deserts, which already occupy approximately a fourth of the Earth's land surface,

have

in

recent

decades

been

increasing

at

an

alarming

pace.

The

expansion

of

desert

-

like

conditions

into

areas

where

they

did

not

previously

exist

is

called

desertification.

It

has

been

estimated

that

an

additional

one

-

fourth

of

the

Earth's

land surface is threatened by this process.

P2

：

Cause

-

1 erosion

-

wind

Desertification

is

accomplished

primarily

through

the

loss

of

stabilizing

natural

vegetation

and

the

subsequent

accelerated

erosion

of

the

soil

by

wind

and

water

(9

-

A). In some cases the loose soil is blown completely away, leaving a stony surface.

In other cases, the finer particles may be removed, while the sand

-

sized particles are

accumulated to form mobile hills or ridges of sand.

P3

：

Cause

-

1 erosion

-

water

Even in the areas that retain a soil cover, the reduction of vegetation typically results

in

the

loss

of

the

soil's

ability

to

absorb

substantial

quantities

of

water

(2).

The

impact

of

raindrops

on

the

loose

soil

tends

to

transfer

fine

clay

particles

into

the

tiniest soil spaces, sealing them and producing a surface that allows very little water

penetration. Water absorption is greatly reduced; consequently runoff is increased,

resulting

in

accelerated

erosion

rates.

The

gradual

drying

of

the

soil

caused

by

its

diminished ability to absorb water results in the further loss of vegetation, so that a

cycle of progressive surface deterioration is established.

P4

：< /p>

Cause

-

2 climate

-

global warming

In

some regions, the

increase

in

desert

areas

is occurring

largely

as the result of a

trend

toward

drier

climatic

conditions.

Continued

gradual

global

warming

has

produced

an

increase

in

aridity

for

some

areas

over

the

past

few

thousand

years

(9

-

B).

The

process

may

be

accelerated

in

subsequent

decades

if

global

warming

resulting from air pollution seriously increases.

P5

：

Cause

-

3 people

There

is

little

doubt,

however,

that

desertification

in

most

areas

results

primarily

from

human

activities

rather

than

natural

processes.

The

semiarid

lands

bordering

the deserts exist in a delicate ecological balance and are limited in their potential to

adjust

to

increased

environmental

pressures.

Expanding

populations

are

subjecting

the land to increasing pressures to provide them with food and fuel. In wet periods,

the land may be able to respond to these stresses. During the dry periods that are

common phenomena along the desert margins, though, the pressure on the land is

often far in excess of its diminished capacity, and desertification results (4).

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页

P6

：

Cause

-

3

people

-

overcultivation

Four

specific

activities

have

been

identified

as

major

contributors

to

the

desertification

processes:

overcultivation,

overgrazing,

firewood

gathering,

and

overirrigation. The cultivation of crops has expanded into progressively drier regions

as

population

densities

have

grown.

These

regions

are

especially

likely

to

have

periods

of

severe

dryness,

so

that

crop

failures

are

common.

Since

the

raising

of

most

crops

necessitates

the

prior

removal

of

the

natural

vegetation,

crop

failures

leave

extensive

tracts

of

land

devoid

of

a

plant

cover

and

susceptible

to

wind

and

water erosion (6).

P7

：

Cause

-

3

people

-

overgrazing

The raising of livestock is a major economic activity in semiarid lands, where grasses

are

generally

the

dominant

type

of

natural

vegetation.

The

consequences

of

an

excessive number of livestock grazing in an area are the reduction of the vegetation

cover and the trampling and pulverization of the soil(9

-

D). This is usually followed by

the drying of the soil and accelerated erosion.

：

Cause

-

3

people

-

firewood gathering

Firewood

is

the

chief

fuel

used

for

cooking

and

heating

in

many

countries.

The

increased

pressures

of

expanding

populations

have

led

to

the

removal

of

woody

plants

so

that

many

cities

and

towns

are

surrounded

by

large

areas

completely

lacking in trees and shrubs. The increasing use of dried animal waste as a substitute

fuel has also hurt the soil because this valuable soil conditioner and source of plant

nutrients is no longer being returned to the land.

P9

：

Cause

-

3

people

-

overirrigation

The

final

major

human

cause

of

desertification

is

soil

salinization

resulting

from

overirrigation.

Excess

water

from

irrigation

sinks

down

into

the

water

table.

If

no

drainage system exists, the water table rises, bringing dissolved salts to the surface

(8). The water evaporates and the salts are left behind, creating a white crustal layer

that prevents air and water from reaching the underlying soil.

P10

：

conclusion

The extreme seriousness of desertification results from the vast areas of land and the

tremendous

numbers

of

people

affected,

as

well

as

from

the

great

difficulty

of

reversing or even slowing the process. Once the soil has been removed by erosion,

only

the

passage

of

centuries

or

millennia

will

enable

new

soil

to

form.

In

areas

where considerable soil still remains, though, a rigorously enforced program of land

protection

and

cover

-

crop

planting

may

make

it

possible

to

reverse

the

present

deterioration of the surface.

Paragraph 1: The deserts, which already occupy(

占据

) approximately(

大约

)a fourth

of

the

Earth's

land

surface,

have

in

recent decades

been

increasing

at an

alarming

pace(

以惊人的速度

). The expansion of desert

-

like conditions into areas where they

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