Level4-Unit2-Part1-Extinction Ev
The earth was formed about 4.6 billion years ago.
The first life appeared about 1 billion years later.
The first plants didn’t appear until around 2 billion years ago.
Until about 580 million years ago, lifeforms were small and microscopic.
Since that time life has evolved into many different types or 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 an extinction event many lifeforms or species of life die out.
The causes of mass extinction events are unsolved mysteries.
These events are not predictable and can happen at any time.
Scientist think that some of them were started by astroid impacts or volcanic eruption‘s.
Events like these can change the global conditions but life depends on.
One major extinction event happened about 66 million years ago.
That event may have been started by a large astroid that hit the earth.
As a result the dinosaurs and about half of all species on the planet died out.
When the astroid 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 astroid hit the earth it caused a huge cloud of dust to enter the atmosphere.
This cloud of dust block to the sun and dark the earth for many months.
Without enough sunlight, plants and plant eating animals quickly died.
With the death, 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 live through the age of the dinosaurs but they couldn’t compete.
With the dinosaurs were removed the mammals were able to complete more successfully.
Once they could compete, mammals evolved to a higher state.
Without extinction event perhaps we wouldn‘t be here today.
