Level4-Unit2-Part1*Learning-
- Listening-Extinction Events 1"
The earth was formed about 4.6 million years ago. The first life appeared about a billion years later. The first plants didn’t appear until around 2 billion years ago. Until around 580 million years ago, life forms were small and microscopic(微笑的). Since that time, live has evolved into many different types, species. However, scientists estimate that more than 99% of them are now extinct.
There have been several extinction events in the history of the earth. In the extinction event many life forms, or species of life, die out. The causes of the mass extinction events are unsolved mysteries. These events are not predictable and can happen at any time. Scientists think that some of them were started by asteroid impacts or volcanic eruptions. Events like these can change the global conditions that life depends on.
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.
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 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.
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 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 the extinction events, perhaps we wouldn’t be here today.
Level4-Unit2-Part1*Learning-
- Listening-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.
Global warming is the result of an increase in carbon gases in our atmosphere. These gases trap heat 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 of many plants and animals. Cutting down forests and polluting rivers destroys the habitats of many forms of life.
There is no longer any doubt that this is happening. Specials of live 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.
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