(单词翻译:单击)
Maybe you remember the first time you saw a dinosaur fossil on display in a natural history museum,
你或许还记得在自然历史博物馆里第一次看恐龙化石展的场景，
or even just a picture of fossils in books and online.
也许甚至记得在书中和网上看过的化石图片。
It's easy to get lost imagining what the world looked like
当这些石骨、爪子和牙齿仍是属于活物的一部分时，
when these stone bones, claws, and teeth were still a part of living creatures.
很容易就沉浸在对世界面貌的想象之中。
But when scientists really want to take themselves back in time, they don't just rely on fossils.
但当科学家们真的想要回顾过去时，他们并不仅依赖于化石。
There are a lot of slightly less glamorous samples,
还有许多不那么耀眼的样本，
from ancient grains of pollen to bubbles of air trapped in ice, that can help us piece together older ecosystems.
从植物花粉粒到空气中的气泡，它们也能帮助我们拼凑出古老的生态系统。
Studying them has even spawned its own field of science, called paleoecology.
对于它们的研究甚至还有了自己的科学领域——古生态学。
And paleoecologists aren't just learning about the past, they're trying to predict the future.
古生态学家不仅只研究过去，还尝试着预测未来。
Researchers find traces of extinct ecosystems in a lot of places,
研究员们在各地寻找灭绝生态系统的痕迹，
including locked in the layers of sediment at the bottom of lakes.
包括在湖底被锁在沉积层中的生态系统痕迹。
New blankets of sediment are laid down constantly, as nearby rocks and minerals break into tiny pieces.
沉积物的新覆盖层不断下沉，附近的岩石和矿物碎成小块。
So the muck gets older the deeper you go,
深入得越深，复盖层的年岁就越久远，
and scientists can use these layers to piece together how things have changed over time.
科学家们可以利用这些覆盖层拼凑出事物是如何随时间而演变的。
For example, thanks to pollen in cores of sediment that were collected from a lake in Indiana,
例如，多亏了从印第安纳州的湖泊里收集的柱状沉积物的岩心，
we know that beech trees became way less abundant in the Great Lakes region of the U.S. starting about 8,000 years ago.
我们了解到自约八千年前，美国五大湖地区的山毛榉树就没有那么繁多了。
Beech trees burn pretty easily.
山毛榉树很容易燃烧。
But in the part of the sediment cores from that time, the patterns of pollen, charcoal, and minerals
但从那时的柱状沉积物的一部分看来，孢粉、活性炭和矿物
hint that drought may have killed off these trees, rather than fire.
暗示着造成这些树木死亡的是干旱而非大火。
Solving these cold cases doesn't just tell us about the past, though.
这些悬案的解决不仅仅告诉我们过去的事。
We can use the stuff in sediment cores to figure out how climate shifts might be related to changes in whole ecosystems.
我们可以利用柱状沉积物中的物质弄清气候突变与整体生态系统变化之间的可能联系。
And that can give us some important clues about how today's anthropogenic,
这能够给我们一些关于当今人类起源的重要线索、
or human-caused, climate change might affect our world in the centuries to come.
或是人为干扰和气候变化会对未来世界造成怎样的影响。
Charcoal particles in lake sediment, for instance, show that the world's boreal forests,
例如，湖泊沉积中的木炭粒子显示世界的北方针叶林，
the evergreen forests around the Arctic, were set ablaze during the Medieval Climate Anomaly.
北极区周围的常绿林在中世纪气候异常期遭遇火灾。
This anomaly was a period of unusually warm temperatures that started around a thousand years ago and lasted several centuries.
这次异常是一段非常不同寻常的高温时期，始于一千年前且持续了几个世纪。
Back then, the warming was caused by a strong fluctuation in ocean currents that changed how heat was distributed around the globe,
那时海流强烈的变动引起了气温上升，改变了全球高温的分布，
which is very different from the changes going on today in the atmosphere.
这和如今大气中的变化非常不同。
But the warming of the Medieval Climate Anomaly is similar in scale to what we're going through now.
但中世纪气候异常期的气温升高和我们现在所经历的相似。
So scientists think that how forests and other ecosystems were affected at the time
因此科学家认为那时的森林和其他生态系统的影响
might be similar to how they'll be affected by today's climate change.
可能和如今由于气候变化对它们所造成的影响也相似。
This means forests in the north should probably brace for more fire.
这意味着北方的森林可能应该为更多的大火做好准备。
So if you thought this year's fire season was bad,
因此，如果你认为今年的火灾季节很糟糕，
history indicates things are poised to go from bad to worse.
历史表明事物随时准备由糟糕变得越来越糟糕。
Clues come from places besides sediment cores, too.
除了柱状沉积物，其线索还来自于其他地方。
Scientists can take cores from big, old trees and examine growth rings to look at weather patterns over time,
科学家们从大而古老的树中获取岩心，然后检测年轮以查看过去的天气模式，
since things like rainfall affect how the rings are spaced.
因为降雨之类的情况能够影响年轮间的间隔。
By comparing tree rings to historical climate records,
通过将树木年轮和历史天气记录相比较，
paleoecologists showed that oak trees in savannas in the midwestern United States
古生态学家发现，美国中西部热带稀树草原上的橡树
became less sensitive to drought over the 20th century,
在过去二十世纪对干旱都没那么敏感，
likely because carbon dioxide levels have been increasing.
这很可能是因为二氧化碳水平的增长。
With more CO2 available, trees and other plants can use it to photosynthesize more.
可用的二氧化碳量越多，树木和其他植物就可利用二氧化碳进行更多光合作用。
When plants open up pores called stomata to take in carbon dioxide, though,
当植物打开气孔吸入二氧化碳时，
they typically lose some water because it evaporates.
由于蒸发，植物会失去一些水分。
But it turns out that many plants have adapted so that their stomata can take in more CO2 without letting too much water escape.
但事实证明许多植物已经适应，因此它们的气孔可以吸入二氧化碳而不流失过多水分。
And this, among other things,
而这一点，尤其是这一点，
makes researchers think that climate change will have complex effects that aren't necessarily predictable.
使得研究员们认为气候变化会产生不可预测的复杂影响。
Thanks to gas bubbles trapped in thick, Arctic ice,
多亏了北极冰中的气泡，
paleoecologists also know that the growing amount of carbon dioxide in our atmosphere is totally unprecedented.
古生态学家同样了解到大气中不断增长的二氧化碳量是完全史无前例的。
Ice cores sampled from some places go back an astonishing 800,000 years.
从其他地方采集的一些冰岩芯样本可追溯到八十万年前。
And in all that time, atmospheric carbon dioxide levels have never risen this quickly.
这么长时间内，大气的二氧化碳水平从未增长的这么快。
So this time, the changing atmosphere could outpace ecosystems' ability to adapt.
因此这一次，变化的大气会超过生态系统的适应能力。
This may sound scary, but we're arming ourselves with knowledge that will help us deal with the challenges ahead.
这听起来可能很可怕，但我们掌握的相关知识能帮助我们提前应对这些挑战。
The more we know about how Earth's ecosystems responded to climate shifts in the past, the more prepared we'll be.
我们对过去地球生态系统如何对气候变化做出反应了解的越多，我们的准备就越充分。
It's like that old saying: those who don't understand the past are doomed to repeat it.
就像那句谚语说的：不了解过去的人注定要重蹈覆辙。
And if you want to arm yourself with more knowledge about the past, check out our sister show Eons,
如果你想了解更多关于历史的知识，请登录我们的姊妹频道Eons，
which dives deep into all the incredible things that have happened on our planet over the past 4.6 billion years.
其中深入介绍了各种发生于46亿年前的星球趣闻。
Just head over to youtube.com/eons and subscribe.
前往youtube.com/eons进行订阅。
