Extinction Events 1
The Earth was formed about 4.6 billion years ago.
The first life appeared about a billion years later.
The first plants didn't appear until around 2 billion years ago.
Until about 580 million years ago, life forms were small and microscopic (微观的).
Since that time, life has evolved into (evolv into 发展成，进化成) many different types, or species (物种).
However, scientists estimate that more than 99% of them are now extinct (灭绝的，绝种的).
Exercise:
1.— When did the first plants first appear on Earth?
— The first plants didn't appear until around 2 billion years ago.
2. Since that time, life has evolved into many different types, or species.
There have been several extinction events in the history of the Earth.
In an extinction event many life forms, or species of life, die out.
The causes of mass extinction events are unsolved mysteries (未解之迷).
These events are not predictable and can happen at any time.
Scientists think that some of them were started by asteroid impacts (小行星撞击) or volcanic eruptions (火山喷发).
Events like these can change the global conditions that life depends on.
Exercise:
1.— What is an asteroid impact?
— It's when an asteroid collides with something.
2. There have been several extinction events in the history of the Earth.
One major extinction event happened about 66 million years ago.
That event may have been started by a large asteroid that hit the Earth.
As a result, the dinosaurs and about half of all species on the planet died out.
When the asteroid hit the earth, it started a chain of events.
A chain of events is a series of events linked together, like a chain.
Exercise:
1.— What may have caused the extinction of the dinosaurs?
— An asteroid hit the Earth and started a chain of events.
2. A chain of events is a series of events linked together, like a chain.
This particular chain of events happened over a period of months and years.
When the asteroid hit the Earth, it caused a huge cloud of dust to enter the atmosphere.
This cloud of the dust blocked the sun and darkened the Earth for many months.
Without enough sunlight, plants and plant-eating animals quickly died.
With the deaths of so many plants and animals, the food chain collapsed.
This led to the deaths of many more species.
Exercise:
1.— What may have darkened the Earth for many months?
— This cloud of the dust blocked the sun and darkened the Earth for many months.
2. Sentence arrange:
(1) When the asteroid hit the Earth, it caused a huge cloud of dust to enter the atmosphere.
(2) This cloud of the dust blocked the sun and darkened the Earth for many months.
(3) Without enough sunlight, plants and plant-eating animals quickly died.
(4) With the deaths of so many plants and animals, the food chain collapsed.
Correct Order: (1) (2) (3) (4)
3. This particular chain of events happened over a period of months and years.
Mass extinction events have played an important part in the evolution of life.
In fact, some extinction events have helped to accelerate evolution.
For example, some mammals lived through the age of the dinosaurs, but they couldn't compete.
When the dinosaurs were removed, the mammals were able to compete more successfully.
Once they could compete, mammals evolved to a higher state.
Without extinction events, perhaps we wouldn't be here today.
Exercise:
1.— What may have blocked the volution of mammals?
— Mammals couldn't compete successfully with the dinosaurs, so their evolution was blocked.
2. When the dinosaurs were removed, the mammals were able to compete more successfully.
Repeat & Read Sentences:
1. There have been several extinction events in the history of the Earth.
2. These events are not predictable and can happen at any time.
3. With the deaths of so many plants and animals, the food chain collapsed.
4. That event may have been started by a large asteroid that hit the Earth.
5. Once they could compete, mammals evolved to a higher state.
Extinction Events 2
Scientists estimate that there have been at least 5 mass extinctions in the last 540 million years.
They also believe that we have entered a new extinction event.
Species are becoming extinct at a much faster rate than before.
Instead of asteroids or volcanic eruptions, the current event is the result of human activities.
Human activities, for example, have led to global warming.
Exercise:
— What is causing the current mass extinction event?
— This new extinction event is caused by humans.
Global warming is the result of an increase in carbon gases in our atmosphere.
These gases trap heat (阻碍热量排放) from the sun, so the Earth is getting warmer.
As a result, sea levels are rising and weather patterns are changing.
In addition, we humans are destroying the habitats (栖息地) of many plants and animals.
Cutting down forests and polluting rivers destroys the habitats of many forms of life.
Exercise:
1.— What traps heat from the sun?
— Carbon gases in the atmosphere trap heat from the sun.
2. Cutting down forests and polluting rivers destroys the habitats of many forms of life.
There is no longer any doubt that this is happening.
Species of life are disappearing at an increasing rate.
Global temperatures are rising and weather patterns are changing.
Scientists are warning us that fast action is necessary to save our future.
If we don't act, we may go the way of the dinosaurs.
Exercise:
1. There is no longer any doubt that this is happening.
Repeat & Read Sentences:
1. If we don't act, we may go the way of the dinosaurs.
2. Species of life are disappearing at an increasing rate.
3. Scientists are warning us that fast action is necessary to save our future.
4. Global warming is the result of an increase in carbon gases in our atmosphere.