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About 66 million years ago, something terrible happened to life on our planet.
大约在六千六百万年以前，我们的星球上的生命遭遇了一次恐怖的劫难。
Ecosystems were hit with a double blow as massive volcanic eruptions filled the atmosphere with carbon dioxide
我们的生态系统遭受了双重打击，空气中弥漫着大规模的火山喷发带来的二氧化碳，
and an asteroid roughly the size of Manhattan struck the Earth.
同时一个体积相当于曼哈顿的小行星撞击了地球。
The dust from the impact reduced or stopped photosynthesis from many plants,
大气中的尘埃严重得影响了许多植物的光合作用，
starving herbivores and the carnivores that preyed on them.
饥饿肆虐着食草动物和捕食它们的食肉动物。
Within a short time span, three-quarters of the world's species disappeared forever,
在很短的时间内，世界上四分之三的物种灭绝了，
and the giant dinosaurs, flying pterosaurs, shelled squids, and marine reptiles that had flourished for ages faded into prehistory.
许多巨型恐龙、飞翼龙、甲壳类软体动物和那些世代繁衍的海洋爬行动物都从我们的史前史中渐渐消失了。
It may seem like the dinosaurs were especially unlucky,
恐龙看上去似乎非常不幸，
but extinctions of various severities have occurred throughout the Earth's history, and are still happening all around us today.
但这却是地球史上适者生存的法则，并且一直延续至今。
Environments change, pushing some species out of their comfort zones while creating new opportunities for others.
环境一直在变化，挑战到一些物种的生存极限，同时也为其它一些物种创造新的机遇。
Invasive species arrive in new habitats, outcompeting the natives.
入侵物种在新的栖息地中战胜原生物种。
And in some cases, entire species are wiped out as a result of activity by better adapted organisms.
有时是整个物种被歼灭，这就是适者生存的法则。
Sometimes, however, massive changes in the environment occur too quickly for most living creatures to adapt,
有时急剧的环境改变让大部分生物来不及自身调整，
causing thousands of species to die off in a geological instant.
导致成千上万的物种在地质突变中灭绝。
We call this a mass extinction event, and although such events may be rare,
我们称之为生物大灭绝，尽管这种事件很罕见，
paleontologists have been able to identify several of them through dramatic changes in the fossil record,
古生物学家已经能从化石记录的戏剧性改变中鉴定出其中的几个案例，
where lineages that persisted through several geological layers suddenly disappear.
例如某些物种化石在几个地质层后突然消失。
In fact, these mass extinctions are used to divide the Earth's history into distinct periods.
我们用这些生物大灭绝事件将地球的历史划分为不同的时期。
Although the disappearance of the dinosaurs is the best known mass extinction event,
虽然恐龙的消失是最有名的大灭绝事件，
the largest occurred long before dinosaurs ever existed.
但是最大的大灭绝是在恐龙出现之前。
252 million years ago, between the Permian and Triassic periods,
2.52亿年前，在二叠纪和三叠纪时期之间，
the Earth's land masses gathered together into the single supercontinent Pangaea.
地球上的陆地聚集成一个超级大的盘古大陆。
As it coalesced, its interior was filled with deserts,
由于陆地中充满了沙漠，在合并的过程，
while the single coastline eliminated many of the shallow tropical seas where biodiversity thrived.
堆积的沙滩湮没了许多生物赖以生息的热带浅海海域。
Huge volcanic eruptions occurred across Siberia, coinciding with very high temperatures, suggesting a massive greenhouse effect.
巨大的火山喷发横跨整个西伯利亚，持续的高温造成大规模的温室效应。
These catastrophes contributed to the extinction of 95% of species in the ocean,
这些灾难促成了95%的海洋生物的灭绝，
and on land, the strange reptiles of the Permian gave way to the ancestors of the far more familiar dinosaurs we know today.
陆地上二叠纪的爬行动物被我们现在熟知的恐龙所取代。
But mass extinctions are not just a thing of the distant past.
然而大规模的生物灭绝并非只是遥远的过去。
Over the last few million years, the fluctuation of massive ice sheets at our planet's poles
在过去的几百万年，地球两极巨大的冰层波动
has caused sea levels to rise and fall, changing weather patterns and ocean currents along the way.
造成了海平面的上升和下降，以及气候和洋流的变化。
As the ice sheets spread, retreated, and returned,
在冰层蔓延和回退的同时，
some animals were either able to adapt to the changes, or migrate to a more suitable environment.
有些动物能够适应这些变化，或迁移去更适合它们的地方。
Others, however, such as giant ground sloths, giant hyenas, and mammoths went extinct.
但是其余的动物，如巨型地懒、巨鬣狗和猛犸象则灭绝了。
The extinction of these large mammals coincides with changes in the climate and ecosystem due to the melting ice caps.
这些巨型哺乳动物的灭绝与气候和生态系统的变化同步，都是由于冰层融化所致。
But there is also an uncomfortable overlap with the rise of a certain hominid species originating in Africa 150,000 years ago.
另一个双重效应就是15万年前某些原于非洲的原始人种的进化。
In the course of their adaptation to the new environment, creating new tools and methods for gathering food and hunting prey,
在适应新环境的过程中，他们创造新的工具和方法来采集食物和狩猎，
humans may not have single-handedly caused the extinction of these large animals,
人类也许并没有直接造成这些大型动物的灭绝，
as some were able to coexist with us for thousands of years.
因为其中的一些动物和我们共存了数千年。
But it's clear that today, our tools and methods have become so effective
但是显然今天我们的捕食工具和方式已经变得如此有效，
that humans are no longer reacting to the environment, but are actively changing it.
人类不再需要适应自然环境，而是开始改变自然环境。
The extinction of species is a normal occurrence in the background of ecosystems.
物种的灭绝在当今生态系统的大背景下已变成一种正常现象。
But studies suggest that rates of extinction today for many organisms are hundreds to thousands of times higher than the normal background.
但研究显示，我们今天许多生物的灭绝率高于自然生态灭绝率的几百至几千倍。
But the same unique ability that makes humans capable of driving mass extinctions can also enable us to prevent them.
人类能够大规模地灭绝生物，也能用同样的能力来阻止它的发生。
By learning about past extinction events, recognizing what is happening today as environments change,
通过对物种灭绝的了解，让我们认识到环境的变化对今天的影响，
and using this knowledge to lessen our effect on other species, we can transform humanity's impact on the world
人类正利用这些知识来减少我们对其他物种的影响，我们可以改变人类对自然界的影响，
from something as destructive as a massive asteroid into a collaborative part of a biologically diverse future.
从如小行星撞击地球般的破坏力的转变为一个和谐共存的生物多样性的未来。
