史上最疯狂的六次生物大灭绝：英语精读讲义

Over 99% of the animal species that have ever lived are now extinct. 語法

曾经存在过的动物物种中，如今已有超过99%灭绝。

And sometimes an event occurs causing changes so drastic 語法

而有时，一场事件会带来极其剧烈的变化，

that most species are completely wiped out within a short period of time. 短語動詞

以至于大多数物种在短时间内彻底消失。

So here are the five most incredible mass extinctions ever to occur

下面就来看看史上最不可思议的五次大灭绝，

and a look at whether the sixth might be happening right now. 語法

以及第六次大灭绝是否可能正在此刻发生。

440 million years ago was the Ordovician extinction.

4.4亿年前发生了奥陶纪大灭绝。

At that time most creatures swam or crawled in shallow seas.

当时，大多数生物都在浅海里游动或爬行。

As newly created volcanic rock was worn down by water and wind, 短語動詞

新形成的火山岩在水和风的侵蚀下逐渐风化，

it reacted with carbon dioxide and absorbed it.

会与二氧化碳发生反应并将其吸收。

As a result, carbon dioxide levels dropped, 表達脈絡

结果，二氧化碳浓度下降，

temperatures fell and water got locked away as ice.

气温降低，水则以冰的形式被封存起来。

This caused ocean levels to drop and shallow seas to drain 語法

这导致海平面下降、浅海干涸，

and after several cycles of growing and shrinking glaciers,

在冰川几经扩张和消退之后，

about 86% of species were lost forever.

约86%的物种永远消失了。

Then over millions of years the oceans slowly repopulated with fish

随后的数百万年间，鱼类慢慢重新遍布海洋，

and the land was colonized by early plants. 用詞

早期植物也开始占据陆地。

These plants were then eaten by the first crawling and flying insects.

随后，最早的爬行和飞行昆虫以这些植物为食。

Then 374 million years ago

到了3.74亿年前，

these new plants contributed to the next mass extinction. 短語搭配

这些新植物又促成了下一次大灭绝。

The plants absorbed enough carbon dioxide to create another round of global cooling.

这些植物吸收了足够多的二氧化碳，引发了新一轮全球降温。

They changed soil causing nutrients to wash into the ocean

它们改变了土壤，使营养物质被冲入海洋，

creating enormous amounts of algae which sucked up oxygen. 短語動詞

催生出大量藻类，而藻类又耗尽了氧气。

More than half of the ocean species essentially choked to death.

超过一半的海洋物种几乎是窒息而死。

Although somewhere in the world a small family of fish with foot-like fins and lungs managed to scrape by. 短語動詞

不过，在世界某个角落，一小群长着足状鳍和肺的鱼勉强活了下来。

Over the next 100 million years these creatures would evolve into amphibians, 語法

在接下来的1亿年里，这些生物逐渐进化成两栖动物、

reptiles, and nearly all modern land animals.

爬行动物，以及几乎所有现代陆生动物。

250 million years ago is the Permian extinction.

2.5亿年前发生了二叠纪大灭绝。

The single worst mass extinction in history,

这是史上最严重的一次大灭绝，

70% of life on land and over 95% of life in the oceans was wiped out.

70%的陆地生命和超过95%的海洋生命被彻底消灭。

Billions of tons of volcanic gases destroyed the ozone layer

数十亿吨火山气体摧毁了臭氧层，

and the average ocean temperature hit 40 degrees Celsius 用詞

海洋平均温度达到40摄氏度，

which is hotter than most hot tubs.

这比大多数热水浴缸里的水还要热。

Acid rain fell all over the planet devastating life on land.

酸雨席卷全球，重创了陆地生命。

Life had only 50 million years to recover until the fourth mass extinction came.

生命只有5000万年的恢复时间，第四次大灭绝便接踵而至。

At this time early small dinosaurs roamed the land.

此时，早期的小型恐龙已经在陆地上游荡。

A huge volcanic rift opened in the middle of the planet

地球中部裂开了一条巨大的火山裂谷，

eventually splitting the Americas from Europe and Africa and forming the Atlantic Ocean.

最终将美洲与欧洲、非洲分开，并形成了大西洋。

The volcanoes spewed out carbon dioxide increasing temperatures 短語動詞

火山喷出大量二氧化碳，推高了气温，

and killing about 80% of the species around at that time.

并杀死了当时约80%的物种。

Yet in this newly emptied world dinosaurs did extremely well

然而，在这个重新变得空旷的世界里，恐龙却极其兴盛，

and during the next 135 million years

在之后的1.35亿年间，

they grew to become some of the largest land animals

它们逐渐成长为一些体型最大的陆生动物，

the world had ever seen. 語法

是这个世界前所未见的庞然大物。

But all good things must come to an end. 習語

但再美好的时代也终会落幕。

Many scientists believe that the extinction of dinosaurs

许多科学家认为，恐龙的灭绝

was caused by an asteroid

是由一颗小行星造成的。

the size of a small town 短語搭配

这颗小行星有一座小镇那么大，

crashing into what is now Mexico's Yucatan Peninsula. 語法

撞上了如今墨西哥的尤卡坦半岛。

The impact shot millions of tons of dust into the atmosphere

撞击将数百万吨尘埃轰入大气层，

blocking out sunlight and spelling an end to all large dinosaurs. 短語搭配

遮蔽了阳光，也宣告了所有大型恐龙的末日。

The small ones that survived evolved into birds.

幸存下来的小型恐龙后来进化成了鸟类。

The world was now primed for a small scuffling rat-like creature, 用詞

世界由此为一种四处窜动的鼠状小生物铺好了舞台，

the ancestor of all modern mammals.

它正是所有现代哺乳动物的祖先。

Within 50 million years its descendants

在5000万年内，它的后代

from wildebeest and whales to horses and us humans

从角马、鲸鱼到马和我们人类，

have diversified and grown to dominate

不断分化壮大，最终占据了

nearly every available environment on Earth.

地球上几乎所有可利用的环境。

So where does that leave us now 65 million years later? 表達脈絡

那么，6500万年后的今天，我们又处于什么境地呢？

Well, human dominance of Earth has led to big changes too

人类对地球的主宰同样带来了巨变，

except the changes of today are happening over decades not millennia. 表達脈絡

不同的是，今天的变化以几十年而非几千年为尺度发生。

Carbon dioxide levels implicated in so many of the past extinctions 用詞

在以往多次大灭绝中都被认为是重要因素的二氧化碳浓度，

have climbed at least 25% in just the last 50 years,

仅在过去50年里就至少上升了25%，

almost no time in geological terms. 短語搭配

从地质尺度来看，这几乎只是一瞬间。

In addition to climate change we've exterminated hundreds of species

除了气候变化，我们还使数百个物种灭绝，

by hunting, fishing, habitat destruction, and pollution.

方式包括狩猎、捕捞、破坏栖息地和污染。

It's been estimated that the current species extinction rates 語法

据估计，目前的物种灭绝速度

are between 100 and 1,000 times higher 語法

要高出100至1000倍——

than the natural background rate

这是相较于自然本底灭绝速度而言；

and that if all the species that are currently threatened

而且，如果目前所有因种群数量下降

by declining populations actually do go extinct, 語法

而受到威胁的物种真的全部灭绝，

we may reach the level of a true mass

我们或许就会达到真正的大灭绝级别，

extinction in just a few hundred years.

而这只需要短短几百年。

And while all the mass extinctions of the past have had some survivors,

尽管过去每次大灭绝都有一些幸存者，

it's worth remembering that the creatures at the top of the food chain 講解

但值得记住的是，处于食物链顶端的生物

are usually hit the hardest.

往往遭受的打击最为沉重。

We may just be setting the stage for history to repeat itself 習語

我们或许正在为历史重演搭好舞台，

and for some small unexpected organism to replace us

让某种意想不到的小生物取代我们，

as the planet's dominant form of life.

成为这个星球上的主导生命形式。

Curious about the coolest animals that existed during these mass extinctions?

想知道这些大灭绝时期有哪些最酷的动物吗？

Check out our new video

快去看看我们的新视频

Five Insane Creatures we wish still existed 語法

《我们真希望还没灭绝的五种疯狂生物》，

over on our AsapTHOUGHT channel

就在我们的AsapTHOUGHT频道上，

which explores some of the neatest and most absurd creatures

视频将带你探索一些最奇特、最荒诞的生物，

through history that are no longer with us. 習語

它们曾存在于历史长河中，如今却已不复存在。

There's a link in the description for that video.

视频链接就在简介中。

And subscribe for more weekly science videos.

别忘了订阅，观看每周更新的更多科学视频。