懂你英语笔记L4U2

L4——U2——1/4listening

Earth forms and extinction

A

1.The earth was formed about four point six billion (46亿) years

ago.

2.The first life appeared about a billion(10亿) years later.

3.The first plant-like didn’t appear until around two billion(20

亿) years ago.

4.Until about five hundred eighty million(五亿八千万) years ago

life forms were small and microscopic(极小的，微小的).

5.Since that time, life has evolved(进化) into many different types

or species.

6.However scientists estimate(估计) that more than ninety nine

percent（99%） of them are now extinct(灭绝的).

B

1.There have been several extinction(绝种) events in the history of

the earth.

2.In an extinction events many life forms or species of life die

out.

3.The causes of mass extinction events are unsolved mysteries(未解

之谜).

4.These events are not predictable(预告) and can happen at any

time.

5.Scientists think that some of them were started by asteroid

impacts(影响，碰击或者装机) or volcanic eruptions(火山爆发).

6.Events like this, can change the global conditions that life

depends on.

C

1.One major extinction event happened about sixty-six million(6600

万) years ago.

2.That event may have been started by a large asteroid that hit the

earth.

3.As a result, the dinosaurs and about half of all species(物种，种

类，类型) on the planet die out.

4.When the asteroids hit the earth, it started a chain of events.

5. A chain of events is a series of events linked together like a

chain.

D

1.This particular chain of events happened over a period of months

and years.

2.When the asteroid hit the earth, it caused a huge cloud of dust

to enter the atmosphere.

3.This cloud of dust blocked the Sun and darkened the Earth for

many months.

4.Without enough sunlight, plants and plant-eating animals quickly

died.

5.With the deaths of so many plants and animals, the food chain

collapsed.

6.This led to the deaths of many more species.

E

1.Mass extinction events have played an important part in the

evolution (演变，发生，进化论) of life.

2.In fact, some extinction events have helped to accelerate(加快，

加速) evolution.

3.For example, some mammals(哺乳动物) lived through the age of the

dinosaurs, but they couldn’t compete(竞争).

4.When the dinosaurs were removed, the mammals were able to compete

more successfully.

5.Once they could compete, mammals evolved to a higher state.

6.Without extinction events, perhaps we wouldn’t be here today. Existence(存在)

F

1.Scientists estimate(估计，预测) that there have been at least

five mass extinctions(五次大灭绝) in the last five hundred forty million years.

2.They also believe that we have entered a new extinction events.

3.Species are becoming extinct at a much faster rate than before.

4.Instead of asteroids or volcanic eruptions the current(最近的)

events is the result of human activities.

5.Human activities for example have led to global warming.

G

1.global warming is the result of an increase in carbon gases(含碳

气体) in our atmosphere.

2.These gases trap heat(阻碍热量排放) from the sun, so the Earth is

getting warmer.