L4-U2-P1 Extinction Events 1 🌍毁灭

The Earth formed by 4.6 billion years ago地球是46亿年前形成的

The first life appeared about a billion year later第一个生命的出现大约10亿年后

The first plants didn't appear until around 2 billion years ago第一个植物知道20亿年前还没有出现

L4-U2-P1 Extinction Events 1 🌍毁灭事件1

Until 580 million years ago life forms were small and microscopic 直到5.8亿年前生命的形式是微小和微观的

Since that time，life has evolved into many types or species 自那时 生命已经进化多种种类

However，scientists estimate that more than 99% of them are  now extinct 然而，科学家估计它们中超过99%现在要灭绝

There have been several extinction events in the history of the Earth 在地球的历史中有几次毁灭的事件

In an extinction event many life forms or species of life ，die out  在一次灭绝事件中许多生命的形式，生命的种类，灭绝

The causes of mass extinction events are unsolved mysteries大规模的灭绝事件原因未被解决的谜题

These events are not predictable，can happen at any time这些事件不能被预测，能发生在任何时间

Scientists think that some of them were started by asteroid impacts or volcanic eruptions科学家认为它们中的一些由小行星撞击或火山爆发引起的

Events like these can change the Global conditions that life depends on这样的事件能改变生命赖以生存的的环境发生改变

One major extinction events happened about 66 million years ago一个主要的我毁灭事件发生大约6600万年前

That event may have been started by a large asteroid that hit the Earth那件事件是由大行星撞击地球引起的

As a result，the dinosaur and about half of  all species on the planet died out 结果，恐龙🦕和地球上一半的种类灭绝

When the asteroid hit the Earth，it started a chain of events当行星撞击地球发生了一连串的事件

A chain of events is a serious of events linked together，like a chain一连串的事件是一个严重的事件联系在一起，像一个链子

This particular chain of events happened over a period of months and years 这一系列特殊的事件发生在几个月甚至几年的时间里

when the asteroid hit the earth it caused a huge  cloud of dust  to enter the atmosphere当行星撞击地球导致巨大的我灰尘云进入大气层内

This cloud of dust blocked the sun and darkened the Earth for many months这灰尘云阻挡了太阳使地球黑暗了数月

Without enough sunlight plants and plant-eating animals quickly died没有足够的我阳光植物和食草动物很快死了

With the deaths of so many plants and animals，the food chain collapsed 随着如此多的植物和动物的死亡食物链崩塌了

This led to deaths of many more species这导致更多种类的生命死亡

Mass extinction events have been played an important part in the evolution of life 在生命的进化中大规模毁灭事件扮演了重要作用

In fact，some extinction events have helped to accelerate evolution 事实上一些毁灭事件帮助加速生命的进化e，some mammals lived through the age of the dinosaurs，but they couldn't compete例如，一些哺乳类生活在恐龙时代，但是他们无法竞争

When the dinosaurs were removed，the mammals were able to compete more successfully当恐龙消失后，哺乳动物能够更成功的竞争

Once they could compete，mammals evolved to a higher state 一旦他们能够竞争，哺乳动物进化到更高的阶段

Without extinction events，perhaps we wouldn't be here today 没有毁灭事件，或许我们今天不能在这里