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10分钟了解四十亿年地球史 – 译学馆
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10分钟了解四十亿年地球史

4 Billion Years in Under 10 Minutes

地球自形成以来的四十五亿年间
Earth has been through a lot
历经了沧海桑田
in the four and a half billion years since it formed.
地球的大部分历史面貌都已被
Most of Earth’s history has been shaped
板块运动带来的大陆间相互碰撞所改变
by plate tectonics, where continents slide around.
与恰好绕开相反的是
But instead of skirting around each other neatly,
大陆之间相互作用的方式
the continents can interact in some
往往会十分地出人意料
pretty unexpected ways.
大陆相聚到一起 又崩裂开来
Continents come together and burst apart
中心位置的岩石却又能保持稳定
while the rocks at their centers stay put.
地壳在地质构造运动和
Earth’s crust is flung upward
大气的风化作用下被不断剥离
by tectonics and weathered back down by the atmosphere.
多年来由此导致了诸多变化
And that’s led to a lot of changes overthe years.
在地球历史的初始阶段
For the earliest part of Earth’s history,
我们根本没有岩石可寻 也就是说
we don’t have any rocks at all, meaning
我们无法直接进行研究
we can’t study it directly.
在生命的第一段时期
For the first part of its life,
这颗行星还是个火球 经常遭遇小行星撞击
the planet was a molten mess, constantly bombarded by
而且不够稳定 难以保存那段历史
asteroids and not stable enough to preserve much record of that time.
因此地球的所有地质史
So any geological history of the Earth
都只能以大陆开始稳定之际为起点
has to start when the continents started to stabilize,
差不多是30到35亿年前
somewhere between 3.5 and 3 billion yearsago.
这些古老岩石上并未记载任何日期
These super-old rocks don’t exactly have dates written on them,
但它们的化学转变
but a quirk of chemistry
却能帮助我们判断它们的年代
can tell us how old they are.
并由此产生了一个全新领域 同位素地球化学
And that has led to an entire field calledisotope geochemistry.
每个原子的原子核中都有
See, each atom comes with a certain number
一定数量的质子和中子
of protons and neutrons in its nucleus.
不同元素的区分靠的是核中质子的数量
Different elements are defined by the number of protons
因此每种元素的原子中
in the nucleus, so the atoms of
都有相同数量的质子
each element all have the same number of protons.
而中子的数量通常有可变的余地
But there’s usually some wiggle room inthe number of neutrons.
举例来说 碳原子有六个质子
For example, carbon has six protons,
而天然的碳原子可以有六到八个中子不等
but natural carbon can have six, seven, or eight neutrons.
这些变体统称为同位素
Those carbon variants are called isotopes,
命名原则也是依据其质子
and they’re named based on how many protons
和中子的数量
and neutrons they have.
因此有六个质子和六个中子的碳原子为碳12
So carbon atoms with 6 protons and 6 neutrons are carbon-12,
六个质子七个中子就是碳13 以此类推
6 protons and 7 neutrons makes carbon-13, and so on.
不同的同位素有不同数量的
Because different isotopes have different numbers
中子 其重量也因此而异
of neutrons in them, they weigh different amounts.
差别细微 却足以让地球化学家们
It’s a tiny difference, but it’s enough that geochemists
区分并计算
can separate them and calculate
每种同位素的数量
how much of each one there is.
有些同位素会随时间衰变
Some isotopes decay over time.
比如 碳14会失去一个质子
Carbon-14, for example, loses a proton
衰变为氮14
and turns into nitrogen-14.
开始是铀238的原子
And atoms that start out as uranium-238
经过不断的衰变 最终全部
decay over and over again until they eventually
变为铅206
become lead-206.
我们已知这些衰变的时长
Because we know how long those decaying processes take,
那么测量已衰变和未衰变的同位素数量之比
the ratio of decayed isotopes to their non-decayed precursors
就可以帮助我们很好地确定某件东西的年代
can give us a good estimate of an object’s age.
铀衰变为铅所需的时间十分漫长
Uranium decays to lead over a very long period of time,
因此不同的铅同位素所占的比例
so the ratio of different lead isotopes
是一种很有用的判定岩石年代的资源
can be a very useful resource in telling the age of a rock.
这只是同位素地球化学中的一种简单方法
And that’s only one of the simpler things isotope geochemistry can do.
导致同位素比例发生变化的原因
Ratios of isotopes can change as a result
除了放射性 还包括各种自然进程
of all sorts of natural processes, not just radioactivity.
碳同位素的比例可以显示出
The ratio of carbon isotopes can show whether carbon trapped
某块矿石中的碳是否被用于光合作用
in a mineral was once used for photosynthesis,
也就能判断其是否曾被用于组成生命体
and therefore was part of something alive at some point.
硫同位素可以用来判断
And sulfur isotopes can be used to show
某块矿石是在地球表面附近
whether a mineral was formed near the surface of the Earth,
还是在更深处形成
or much farther down.
同位素地球化学可以提供给我们
Isotope geochemistry gives us all kinds of information
这世界上最古老岩石的各种信息
about the world’s oldest rocks.
这些远古的石头又能帮我们
And those ancient rocks give us a way
拼凑出大陆板块的浮沉历史
to piece together the history of the continents,
包括板块运动带给它们的移变
including the way plate tectonics has shifted them around.
板块构造的存在是因为地球像洋葱一样有着分层
Plate tectonics are a thing because Earth, like an onion, has layers.
有些分层是固态 有些则更有流动性
Some layers are solid and some are more fluid.
最外层当然是固态
The outermost layer is, obviously, solid.
即岩石圈
That’s the lithosphere,
它构成了托起大陆与海洋的底盘
which makes up the plates that hold the continents and oceans.
向下一层则有些液体特征
Underneath that is a layer that is little bit more liquid-y,
岩石就漂在这上面
where rock is flowing.
该层的运动推动着大陆
That movement pushes the continents around,
也就造成了板块运动
which gives us plate tectonics.
但是有一个问题:并非圈圈生而平等
But there’s a catch: not all lithosphereis created equal.
支撑大陆的地壳
The crust that holds up the continents is
比海洋底部的厚 密度要小
thicker and less dense than the crust beneath the oceans.
大陆板块漂浮得很好
The continental crust floats really well,
你可以想象一块数千千米厚的
if you can imagine a slab of rock thousands
岩石平板在那漂着
of kilometers across floating.
这就意味着 海洋板块与大陆板块相遇时
That means, when oceanic crust and continental crust meet up,
前者容易被推到下面
the oceanic crust tends to get shoved underneath
通过一种叫做俯冲作用的过程而消失
and melted in a process called subduction.
大陆板块则向上仰冲
The continental crust rides on top
得以幸存 有朝一日再次碰撞
and survives to collide another day.
也就是说每片大陆的某些块
And that means that certain chunks of every continent
都有三十亿年及以上的历史
go back as much as three billion years or more.
这些超稳定的陆地块叫做稳定地块
These super-stable continental chunks arecalled cratons.
它们由坚硬而又能浮动的岩石组成
They’re made of tough, floaty rock
而这些岩石已经存在至少三十亿年
that often hasn’t been melted by plate tectonics
在板块运动中成功逃生了
for three billion years or so.
最年轻的一批存在了大约五亿年
The youngest ones clock in around half a billion.
在地球还是熔岩遍地的大火球时期
Back when Earth was still a liquidy mess of molten rock,
更重的元素缓慢地向地核下沉
the denser elements slowly sank towards the core.
就像油会浮到水面上一样
And just like oil floats on top of water,
轻的元素上浮到表面
the less dense elements rose toward the surface.
所以大陆板块大多是由
So continental crust is mostly made of
相对较轻的富含二氧化硅的岩石构成
relatively light rocks rich in silica.
随着这些轻石头逐渐冷凝下来
As these light rocks started to cool and condense,
它们会像软木塞一样
they would have bobbed like a cork
在地球表面鼓起来
on the surface of the planet.
这些能浮起来的小塞子会互相挤压
Those little floaty corks would have bashed into each other
但不会一个俯冲到另一个下面
and instead of one subducting under the other,
而是粘连到一起
they would have stuck together.
一段时间后就成了大木塞了
After a while, you would get bigger floaty corks.
这些大块开始稳定下来
These chunks really started to stabilize
逐渐变为大陆
into continents during the Archean eon,
时间大概在25到40亿年前的太古宙
about 4 billion to 2.5 billion years ago.
这一时期的稳定地块构成了第一批大陆的核心
Archean cratons formed the nuclei of the first continents,
且从此以后就滞留在这个状态
and they’ve stuck around ever since.
地理学家们认为大多数大陆的构建
Geologists think that most continent building happened
都开始在太古宙之前 而大部分形成在此阶段之后
way back then and was pretty much done after that.
当然 板块运动帮助重造了很多
Sure, they’ve rearranged a ton by plate tectonics,
但很多的陆地
but much of the actual land is
自太古宙时期就已存在 仍是一样的
the same land that existed in the Archean.
而有证据表明
But some evidence suggests
有时候地球内部的轻岩石仍能浮上来
that lighter rock can still bubble up from inside Earth sometimes
增添成为星星点点的陆地
and add new bits and pieces.
你可能听过盘古大陆
You might heard of Pangea,
就是恐龙时代存在的超大陆
the supercontinent that existed around the time of the dinosaurs.
地理学家认为其只是最近一次
Geologists think Pangea is only the latest supercontinent
行星撞击周期中的一个超大陆
in a planetary boom and bust cycle,
这种聚成与崩裂是会频繁发生的
where supercontinents assemble andbreak up every so often.
他们此对此事发生的原因不能完全确定
They aren’t totally sure why this happens,
但主流的说法是
but the leading hypothesis is that
这些厚重的大陆板块构成的巨大障碍
those big blocks of thick continental crust
困住了底部的大量热能
trap lots of heat beneath them.
最终 被困住的热量以岩浆热柱的形式
Eventually, the trapped heat bubbles over in the form
喷薄而出 喷得超大陆分崩离析
of magma plumes and blows the supercontinent apart,
就像慢动作下被撞开的台球一样
like billiard ballsbreaking up in slow motion.
各片大陆相互分开 直到下次相遇时
Then the pieces bounce around until they meet up again,
大陆板块又会粘连到一起
with continental crust sticking together,
而不是发生俯冲
instead of getting subducted.
这样 下一个周期又开始了
And the cycle begins again.
地理学家对地球上的大陆
Geologists have a pretty good understanding
一直以来的运动有着非常不错的理解
of how Earth’s continents have moved around over time,
而这是基于像拼图一样对岩石进行匹配得来的
which they’ve figured out by essentially matching up rocks like puzzle pieces.
板块构造学说首次被部分提出是基于
Plate tectonics was first proposed in part based on
南美洲与非洲轮廓恰到好处的相互拼合
how neatly South America and Africa fit together,
其暗示了它们都曾是同一片广袤大地——
suggesting they were once part of
盘古大陆的一部分
the same landmass–Pangea.
对更古老的超大陆的探寻也是如此
Hunting for older supercontinents is like that too,
但难度系数要上升到11
but with the difficulty ramped up to 11.
地理学家使用的主要工具叫做古地磁学
The main tool geologists use for this is called paleomagnetism,
使用这一工具主要是基于
which is based on the fact
地球磁场会规律性地发生反转
that Earth’s magnetic field regularly reversesitself.
岩石在形成时
When a rock forms,
其中的任何磁元
any magnetic bits in it
都会与地球当时的磁场对齐
will line up with Earth’s magnetic field at the time.
也就是说 含有磁性粒子的岩石
That means a rock containing magnetic particles
会反映出其形成时
will reflect where Earth’s magnetic field
地球磁场的指向
was pointing when the rock formed.
由于磁场的反转
And since the magnetic field reverses on the order
为数千年一次
of thousands of years,
这就为我们探寻数十亿年来发生的事
that provides a ton of data when we’re looking
提供了海量的数据
at things that happened over billions of years.
利用数学 我们能十分精确地找到
Using math, we can pinpoint pretty accurately
所需的岩石究竟在何处
where on Earth the rock was.
大陆在这漫漫地球史中都去了哪
The question of where the continents have been
仍是个颇具挑战性的问题
throughout Earth’s history is a challenging puzzle,
并非轻易就能解决
and one that’s far from being solved.
不过我们还是有可以使用的工具
But we do have some tools that we can used to figure it out,
地理学家也有关于
and geologists have some ideas about
泛大陆之前聚集成的超大陆的看法
the supercontinents that assembledbefore Pangea.
我们把最开始的那个叫做乌尔大陆
We call the very first continent Ur,
它是第一个由小岛屿形成的大片陆地
and it was the first big bit of land to form from small islands.
乌尔大陆存在于约三十亿年前
Ur goes back about three billion years,
组成它的陆地可以在今天的非洲
and was made up of bits of what is now Africa,
澳大利亚和印度找到 或许还有南极
Australia, India, and maybe Antarctica.
实际上 乌尔大陆在盘古大陆形成时才分裂
In fact, Ur only broke up recently, when Pangeadid.
一块大陆能维持将近三十亿年
A continent that can last nearly three billion
真是大陆中的佼佼者
years is one heck of a continent!
一些证据指向比乌尔还要古老的大陆的存在
Some evidence points to a landmass even older than Ur,
它被称为瓦巴拉大陆 能追溯到36亿年前
known as Vaalbara, as far back as 3.6 billion years ago,
但关于其存在的证据还不够确凿
but the evidence for its existence isn’t conclusive.
乌尔大陆最终加盟了更多新生大陆
Ur was eventually joined by more brand new continents,
如北极大陆 大西洋大陆和妮娜大陆
like Arctica, Atlantica, and Nena.
顺便说下 这些大陆可能名字很奇怪
By the way, these continents might have odd-sounding names,
但如果你把它们拆开来看的话 你会发现
but if you pick them apart you’ll realize that
它们很多都是很多单词杂糅在一起
a lot of them are smashed-together words
来表示其中包含的陆块
to represent the smashed-together landmasses.
举个例子 Nena这个名字
Nena, for example,
就取自Northern Europe(北欧)
gets its name from the first letters of
和North America(北美)这些单词的首字母
Northern Europe and North America.
上述大陆都被认为
All these continents are thought to have joined up
曾在大约19亿年前
about 1.9 billion years ago to form the
参与组成过第一个
first supercontinent that can be identified
具有几分可信度的超大陆 即哥伦比亚超大陆
with some degree of confidence, called Columbia.
哥伦比亚超大陆持续到约15亿年前才分裂
Columbia lasted until about 1.5 billion years ago, when it broke up.
大陆碎片分而又合
The pieces then rebounded and joined up
在大约11亿年前形成了罗迪尼亚超大陆
to form the supercontinent of Rodinia about 1.1 billion years ago.
在此之后 可能又
After Rodinia, there may have been
短暂存在过一个叫潘诺西亚的超大陆
a very short-lived supercontinent called Pannotia,
但4亿5000万年前盘古大陆的形成
but things were definitely on their way to becoming Pangea
是可以确定的
by 450 million years ago,
并在约2亿5000万年前达到全盛
and at maximum scrunchiness around 250 millionyears ago.
然后1亿7000万年到一亿年前之间
Then between 170 and 100 million years ago,
盘古大陆分裂为我们今天熟知的大陆
Pangea broke up into the continents we know today.
我们正跟踪另一个超大陆
We’re on track for another supercontinent
时间差不多是在2亿5000万年后
in about 250 million years, give or take.
如果南北美洲继续向西漂移
If North and South America continue to drift westward
横渡太平洋 它们会与俄国相遇
across the Pacific, they’ll meet up with Russia
并形成阿美西亚超大陆
and form the supercontinentof Amasia.
现在这些大陆之间推来搡去
Now all those continents shoving each other around
对我们这个地面上的世界
doesn’t come without consequences
不是没有影响的
for our world on the surface.
正是这样才有了各种山——
That’s actually how we get mountains–
各板块边界处常常会有造山运动
the boundaries between tectonic plates often produce mountain ranges.
海洋板块俯冲到大陆板块下面时
When oceanic crust is subducted under continental crust,
后者相应地被向上推起
the continental crust is shoved upward to compensate.
南美洲的安第斯山脉就是个典型
The Andes in South America are a good exampleof that.
当两个更富有弹性的大陆板块相遇时
When two pieces of more-resilient continental crust meet up,
结果会更具戏剧性
the results can be even more dramatic.
大陆板块不会向下俯冲
Continental crust doesn’t tend to subduct,
所以就会有点向上折叠
so instead it just kind of folds upward.
甚至于 即便基于同样的过程形成了山
And even when mountains form through the same basic process,
它们互相之间
they can still look hugely
还是会差异巨大
different from one another.
一个关键的不同在于年龄
One key difference is their age.
北美洲的阿巴拉契亚山脉
The Appalachian mountains in North America
比个山丘高不了多少
aren’t much more than hills at this point,
跟别的山脉比 基本就是风景秀丽 有点起伏的山坡而已
basically scenic, rolling slopes compared to some other mountain ranges,
就像是亚洲的喜马拉雅山脉
like the Himalayas in Asia,
这颗星球上最雄伟的山脉 同时也是珠峰所在
the greatest mountain range on the planet and home to Mt. Everest.
但阿巴拉契亚曾一度高过喜马拉雅
But the Appalachians were once even tallerthan the Himalayas.
二者形成的原因类似
The Appalachians and the Himalayas were formedin similar ways:
喜马拉雅诞生自印度次大陆向亚洲的冲撞
The Himalayas came from the Indian subcontinentcrashing into Asia.
印度必须横渡大洋来到达那里
India had to cross the ocean to get there,
这也就意味着其北边的海洋部分板块
meaning the oceanic crust north of it was
要俯冲到青藏高原下面
subducting under the Tibetan plateau.
但这片次大陆以其厚实的稳定地块撞了上去
But then the subcontinent hit, with its thick,cratonic continental crust.
印度与青藏高原直接对撞
India and the Tibetan plateau crunched directly
并像手风琴一般发生了折叠
into one another and folded up like an accordion.
这一切都发生在相对来说的近期
All this happened relatively recently,
差不多4000万年前
within the last 40 million years or so.
实际上 这一过程仍在继续
In fact, it’s still happening,
喜马拉雅山脉仍在长高 尽管
and the Himalayas are still growing, although that growth
风化与侵蚀作用可能与之相消
might be matched by weathering and erosion.
时间足够长的话 风化作用可能会大幅地
Given enough time, weathering can shrink mountain ranges
削减山脉 如同在阿巴拉契亚所发生的一样
by a lot, which is what happened to the Appalachians.
阿巴拉契亚山脉形成于
The Appalachian mountains formed when
盘古大陆形成时期北美与非洲板块
the North American and African plates collided
之间的相互碰撞
during the formation of Pangea.
那时的它可能比今天的喜马拉雅
They might have been even taller and more impressive
还要高大与震撼
than the Himalayas are now,
两个大陆板块奋力向前 毫不退让
with two continental plates colliding and refusingto give way.
但那是将近5亿年前的事了
But that was almost 500 million years ago,
5亿年足够让风雨
and 500 million years is enough time for
将阿巴拉契亚消磨殆尽
a lot of rain and wind to wear the Appalachiansdown.
因此 巨大的陆地相撞相离
So, huge continents smash together and break apart.
一条条山脉生而复灭
Mountain ranges form and wear back down.
即使我们无法在一旁看到这些事情的发生
And even though we weren’t around to see those things happen,
我们仍可以通过脚下的岩石去了解这一切
we can still learn about them just by studying rocks.
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视频概述

天下大势合久必分,分久必合,地球面貌也是如此。四十亿年间,地球历经了沧海桑田,陆海沉浮。

听录译者

收集自网络

翻译译者

伽卡

审核员

审核员HL

视频来源

https://www.youtube.com/watch?v=DHWavJf4SLE

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