Extinction events 1
The Earth was formed about 4.6 billion years ago.
地球形成于46億年前。
The first life appeared about a billion years later.
第一個(gè)生命出現(xiàn)在大約十億年后。
The first plants didn't appear until around 2 billion years ago.
第一批植物直到20億年前才出現(xiàn)。
Until about 580 million years ago, life forms were small and microscopic.
直到大約5.8億年前，生命形式都是微小的，只能用顯微鏡觀察。
Since that time, life has evolved into many different types, or species.
從那時(shí)起，生命進(jìn)化成許多不同的類型或物種。
However, scientists?estimate that more than 99% of them are now extinct.
然而，科學(xué)家估計(jì)其中99%以上已經(jīng)滅絕。
There have been several extinction events in the history of the Earth.
在地球的歷史上發(fā)生過(guò)幾次大滅絕事件。
In an extinction event many life forms, or species of life, die out.
在一次滅絕事件中，許多生命形式或生命物種滅絕。
The causes of mass extinction events are unsolved mysteries.
大滅絕事件的起因仍是未解之謎。
These events are not predictable and can happen at any time.
這些事件是不可預(yù)測(cè)的，并且會(huì)在任何時(shí)候發(fā)生。
Scientists?think that some of them were started by asteroid impacts or volcanic eruptions.科學(xué)家認(rèn)為其中一些是由小行星撞擊或火山爆發(fā)引起的。
Events like these can change the global conditions that life depends on.
像這樣的事件可以改變生活所依賴的全球環(huán)境。
One major extinction event happened about 66 million years ago.
大約6600萬(wàn)年前發(fā)生了一次大滅絕事件。
That event may have been started by a large asteroid that hit the Earth.
這一事件可能是由一顆撞擊地球的小行星引起的。
As a result, the dinosaurs and about half of all species on the planet died out.
結(jié)果，恐龍和地球上大約一半的物種滅絕了。
When the asteroid hit the earth it started a chain of events.
當(dāng)小行星撞擊地球時(shí)，它引發(fā)了一連串的事件。
A chain of events is a?series?of events linked together, like a chain.?
一連串的事件是一系列相互聯(lián)系在一起的事件，就像一條鏈。
This particular chain of events happened over a period of months and years.這種特殊的連鎖反應(yīng)發(fā)生在幾個(gè)月甚至幾年的時(shí)間里。
When the asteroid hit the Earth, it caused a huge cloud of dust to enter the atmosphere.當(dāng)小行星撞擊地球時(shí)，它引起了巨大的塵埃云進(jìn)入大氣層。
This cloud of the dust blocked the sun and darkened the Earth for many months.
這片塵埃云擋住了太陽(yáng)，使地球黑暗了好幾個(gè)月。
Without enough sunlight, plants and plant-eating animals quickly died.
沒(méi)有足夠的陽(yáng)光，植物和食草動(dòng)物很快就死了。
With the deaths of so many plants and animals, the food chain collapsed.
隨著這么多動(dòng)植物的死亡，食物鏈崩潰了。
This led to the deaths of many more species.
這導(dǎo)致了更多物種的死亡
Mass extinction events have played an important part in the evolution of life.
大滅絕事件在生命進(jìn)化中扮演了重要的角色
In fact, some extinction events have helped to accelerate evolution.
事實(shí)上，一些滅絕事件有助于加速進(jìn)化。
For example, some mammals lived through the age of the dinosaurs, but they couldn't compete.
例如，一些哺乳動(dòng)物生活在恐龍時(shí)代，但他們不能競(jìng)爭(zhēng)。
When the dinosaurs were removed, the mammals were able to compete more successfully.
恐龍滅絕后，哺乳動(dòng)物的競(jìng)爭(zhēng)更加激烈。
Once they could?compete,?mammals evolved to a higher state.
一旦它們能夠競(jìng)爭(zhēng)，哺乳動(dòng)物就進(jìn)化到一個(gè)更高的狀態(tài)。
Without extinction events, perhaps we wouldn't be here today.
如果沒(méi)有滅絕事件，也許我們今天就不會(huì)在這里。
