BBC轨道：地球的非凡之旅（2012）（1）

这是一片珊瑚
It is a piece of coral.
它看起来像一块无关紧要的石头
I know it looks like an insignificant bit of rock,
但对于专家来说 这犹如一本史书
but, to the expert eye, this is as good as a history book.
它详实地记录了
And it gives a really faithful record
远古地球生命体的真实面貌
of what life on earth was like, way back then.
这些是日轮 就像现代珊瑚
There are rings, just like the modern coral.
真正令人惊奇的是
What's really surprising, though,
如果你数数这些成长日轮
is that if you count those daily growth rings,
会有410个日轮
you'll get a total of 410.
四十亿年前
400 million years ago,
一年不是365天
a year lasted not 365 days
而是410天
but 410.
因此 像这块具有410个日轮的古珊瑚
So, the explanation for ancient corals like this piece
其形成原因是
to have 410 daily growth rings
当它存活时
is that when this was alive,
一天只有21个小时 而不是24个小时
a day wouldn't have lasted 24 hours but only 21.
因为那时 地球自转速度更快
And for that to happen, the earth had to be spinning faster.
为了探明原因
To find out why,
你必须回到地球形成初期
you have to go back to the earliest days of the earth's history.
四十五亿年前
4.5 billion years ago,
地球被另一颗行星撞击
the earth was hit by another planet.
产生的碎片形成了月球
Debris from the impact created the moon,
当时月球比现在更接近地球
which would have been much closer to the Earth than it is today.
也使地球自转得更快
It also set the earth spinning much faster.
当海洋开始形成时
When the first oceans formed,
这种组合意味着
that combination would have meant
潮汐非常巨大
the tides would have been simply huge.
想像一下 如今的小潮汐
Just imagine, instead of these small tides
只有几米高
of a few metres that we have today,
但那时却是几百米高的大潮汐
there would be enormous tides, hundreds of metres high,
冲刷着世界各地的海岸线
crashing into the coastlines all around the world.
但随着月球引力牵引着这些潮汐
But as the moon's gravity pulled on these huge tides,
其势头减弱
it acted as a kind of brake.
慢慢地 这使地球减速
Gradually, this slowed the Earth down.
在此过程中
And the same process meant
月球慢慢远离地球
that the moon drifted gradually further away.
随着月球渐行渐远
As the moon got further away,
它的引力作用逐渐减弱
its gravitational pull on the tides decreased,
于是潮汐逐渐变小
so the tides got lower.
即便是今天 地球的自转也在逐渐减慢
But, even today, the rotation of the Earth is slowing down
我们的白天越来越长
and our days are still getting longer
但每个世纪只增加2.3毫秒
but only by about 2.3 milliseconds every century.
我们逐渐步入冬天
We're now heading into winter.
因为地球的倾斜角度越来越大
Because of the Earth's angle of tilt,
北半球倾斜到
the northern hemisphere is leaning
越来越远离太阳
further and further away from the sun
因此气温降低 昼短夜长
So temperatures are falling and the days are getting shorter.
自然世界以停工来应对冬季
The natural world responds by starting to shut down.
树木检测到白日逐渐变短
Trees detect the shortening day length
绿叶就开始停止制♥造♥二氧化碳
and stop producing green chlorophyll in their leaves.
金色染黄秋季
The golden colours of autumn take over.
大雪普降
The snow begins to fall.
在黄石公园 黑熊
In Yellowstone Park, black bears
寻找洞穴过冬
head for their dens and winter hibernation,
100天不吃不喝
100 days without eating.
鸟儿们比如雪雁
Birds like snow geese,
曾在北极度夏 现在往南飞
that spent the summer in the Arctic, now head south,
成群结队
often in huge numbers,
前往更暖和的地区过冬
to spend the winter in more temperate climes.
十一月末
By the end of November,
北极的大部分区域经历着全天的黑暗
most of the Arctic is experiencing 24 hours of darkness.
极夜
The polar night.
现在是十二月初
It's now early December
我们的旅行也快要结束了
and we are coming towards the end of our journey.
我们终点站是地球自转
Our final destination is a place where the Earth's rotation
对气候有极大影响的地方
has a particularly powerful impact on the weather.
英国
Britain.
英国应该是一天中天气变化之剧
You can't imagine a day that's more typical
最为典型的地区了
of what we think of British weather.
今早我们到达时 天正在下雨
We arrived this morning and it was raining
然后太阳出来了 之后又起风了
and then the sun came out and then there was a squall,
然后太阳又出来了
and now the sun's come out again
同时伴随着狂风
and we've got this really strong wind.
英国的天气是众所周知的难以预料
The British winter is notoriously unpredictable.
有时寒冷干燥 有时温暖湿润
Sometimes cold and dry, sometimes mild and wet.
这种不可预知性是地球自转的结果
This unpredictability is a consequence of the Earth's rotation.
关键原因是英国的地理位置
The key factor is Britain's location.
我们现在位于
We sit underneath the boundary
地球两个气候带的交界处
between two of the Earth's climate cells.
这意味着 在我们头上
This means that, above our heads,
有两种不同类型的气流交锋
there's a battle going on between two different types of air.
我画一张地图来说明
I'm going to draw a map to show you.
这是南海岸
This is the south coast
苏格兰在这上面
and Scotland's up here.
我们在下面康沃尔这里
And we're down here, in Cornwall.
爱尔兰在那里
And Ireland is out here.
在上面 我们的北部 有寒冷极地气流
Up here, to the north of us, there's cold, polar air,
在下面 我们的南部
and down on this side, to the south,
有来自赤道的暖气流
is warm air that's come from the tropics.
这两种气流的交锋处
And the boundary between the two
就在不列颠群岛上
can lie right over the British Isles.
我们头上发生的事情是
And what's going on above our heads
冷暖气流的对冲
is a clash of the cold air and the warm air
它们在那里
and it's where they're
相互推挤融合
pushing against each other and mixing it up
于是就形成了这种易变的天气
that we get this changeable, messy weather
英国人最喜欢抱怨他们的天气了
that we love to complain about in this country.
2011年12月 我们目睹了这场交锋
In December 2011, we saw this battle in action.
当冷暖气流在我们头顶上争夺霸权时
A succession of storms battered the country
一系列风暴席卷英国
as warm and cold air struggled for supremacy above our heads.
但还有更深层次的原因
But there's a further factor
影响着冷暖气流
that influences the outcome
交锋的结果
of this battle between warm and cold air.
这气候带的边界可能会移♥动♥
The boundary between the cells can move.
这种移♥动♥由两个气候带边界
This movement can be affected by a phenomenon that's generated
形成的一种现象所影响
right at the boundary between the cells.
这是地球自转的结果
And it's a product of the Earth's spin.
就在边界上 天际中
Right at the boundary, high up in the sky,
一阵风高达十千米
a wind blows about 10 kilometres up.
风速极快
It's really, really fast.
风速可达每小时450公里
It can travel at speeds of up to 450 kilometres per hour.
它环绕整个地球 横跨所有纬度
It coils all the way around the planet, at about our latitude,
我们称其为急流
and we call it the jet stream.
这股急流很关键
The jet stream is crucial
因为它影响北部寒冷气流
because it influences the boundary between the cells,
和南部的暖气流
and therefore between cold air to the north
之间的边界
and warm air to the south.
你可以通过前一年12个月的
You can see the significance of this
气象变化看出其重要性
by looking at the weather 12 months earlier,
在二零一零年十二月
in December 2010.
英国饱受冰雪之灾
The whole country shivered under a blanket of snow and ice.
这是有史以来最冷的寒冬
It was one of the coldest winters since records began.
原因是急流发展出了一个扭结
The reason was that the jet stream had developed a kink.
在大西洋上空 它向北移♥动♥ 靠近北极圈
Over the Atlantic, it sat much further north, near the Arctic.
然后在英国上空下降
Then it swung down, over Britain.
这暂时改变了两个气候带的边界
This temporarily shifted the boundary between the cells
将寒冷的北极气流带至英国
and brought cold, polar air across the whole country.
遗憾的是 我们的天气预报
Unfortunately for our weather forecasters,
很难预测出
it's particularly difficult to predict
急流的曲线运动
the meanderings of the jet stream.