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地中海消失之谜

That Time the Mediterranean Sea Disappeared

In 2011, paleontologists working on the Spanish island of Minorca
2011年 研究西班牙梅诺卡岛的古生物学家
announced the discovery of some very odd fossils.
宣布了发现了一些奇特的化石
They were the bones of a rabbit,
这些是兔子的骨头
but it wasn’t like any rabbit you’ve ever seen.
但并不属于任何一种我们所知的兔子
For one thing, this bunny was a giant,
一个原因是 这种兔子体型巨大
up to six times heavier than your average cottontail.
最大能达到棉尾兔重量的7倍
It also had short hindlimbs, compared to its forelimbs,
同时 相比前腿 它的后腿更短
and feet that were tipped with claws.
足尖还有利爪
And this rabbit almost certainly couldn’t hop.
几乎可以肯定 这种兔子无法蹦跳
It had a stiff spine and splayed toes
它脊柱坚硬 脚趾分开
very different from the flexible spines and tightly packed toes of living rabbits.
这与现存兔子弹性的脊柱和紧密排列的脚趾 完全不同
They named this huge bunny Nuralagus rex — “the Rabbit King of Minorca”
科学家将巨兔命名为梅诺卡兔王
and they determined that it ruled its island kingdom during the Pliocene Epoch,
他们还发现巨兔在上新世统治这座岛屿王国
from about 5 million to 3 million years ago.
时间大约是五百万到三百万年前
Now, we’ve talked before about insular gigantism,
我们曾经介绍过岛屿巨型化的概念
where small animals that become isolated on islands
它是指小型动物被隔绝在孤岛上
evolve into larger forms due to a lack of predators.
由于缺少天敌而演化成更大的体型
And that seems to be what allowed Nuralagus rex to get so big.
这可能是梅诺卡兔王如此巨大的原因
But how did the normal-sized ancestor of Nuralagus
但它的正常体型的祖先
make it onto a Mediterranean island in the first place?
最初是如何成功抵达地中海孤岛上的呢?
Well, it looks like the answer to this biological mystery
看起来 这个生物谜题的答案
is actually wrapped up in an even older geological mystery.
实际上隐藏在一个更古老的地理谜题中
Since the 1800s, scientists have known that the layers under the floor of the Mediterranean
19世纪以来 科学家已发现地中海的地层
Sea weren’t just made up of the usual sediments, like mud and sand.
并非仅由泥土和沙子这类的普通沉积物构成
Instead, they’re full of salt crystals — lots and lots of salt —
而是充满了盐晶体 非常大量的盐晶体
forming mega-deposits
并从而形成大型盐矿床
so large that they’re sometimes called the Mediterranean Salt Giant.
储量大到被有时也称为地中海巨盐矿
And salt deposits like these are typically found in places
类似的盐类沉积层一般在
where bodies of water have dried up.
水域干涸后的地方出现
So the existence of this Salt Giant suggests that,
所以巨盐矿的出现意味着
at one point in history, the Mediterranean Sea must have evaporated.
在历史上的某个时期 地中海水曾蒸发过
But how could a body of water
但像地中海这样如此巨大的水域
as big as the Mediterranean sea just…disappear?
怎么会轻易消失呢?
It would take decades and more than 1,000 research studies
这大概需要花费数十年和上千项的研究
to even start to figure out the cause –or causes
才能对这场地球上最大的消失之谜之一
of one of the greatest vanishing acts in Earth’s history.
稍稍理出一丝头绪
Today, ocean water flows into the Mediterranean Sea from the Atlantic
今天 海水从大西洋流向地中海
through a narrow passage between Europe and Africa,
要经过欧洲和非洲之间的一条狭窄通道
called the Strait of Gibraltar.
名为直布罗陀海峡
And that’s the main source of water for the Sea.
而这是地中海水的主要来源
Some freshwater in the form of rainfall and rivers also flows into it,
一部分淡水会通过降雨和河流进入地中海
but that’s not enough to keep the Sea filled up
但是 没有大西洋流入的海水
without the water from the Atlantic,
这些淡水并不足够一直填满地中海
because it has very high rates of evaporation.
因为这里的海水蒸发量非常高
So, to the geologists who were trying to explain the existence of the Salt Giant,
因此 对于试图解释巨盐矿现象的地理学家来说
it looked like the main water source to the Mediterranean had somehow been turned off,
似乎地中海的主要水源不知怎的被切断了
like turning off a faucet in a bathtub.
就如同浴缸的水龙头被关掉那样
They called this event the Messinian Salinity Crisis, or MSC.
他们把这一现象称为墨西拿盐度危机 简称盐危机
But it wasn’t easy to figure out
但是 要弄清水源为何会被切断
how that water source got turned off.
并非一件容易的事情
And researchers have been arguing about it
自1970年代以来
since the 1970s.
研究人员就一直争论不休
How did it happen?
它究竟如何发生?
How long did it take?
持续了多长时间?
In the end, they came up with three main hypotheses
最终 他们总结出三种假说
to answer these questions and explain how the salt giant got there.
来回答以上问题和解释巨盐矿的成因
First, some scientists thought there was a global cooling event
首先 一些科学家认为盐度危机开始时
at the beginning of the crisis,
全球正经历降温现象
in the Late Miocene Epoch around 6 million years ago.
当时正是约六百万年前的中新世
If the whole world cooled off into an ice age,
如果全球降温并进入冰川时期
then lots of water would’ve been taken out of the ocean and frozen in glaciers,
大量的海水就会变成冰川
reducing the water flow into the Mediterranean Sea
无论是从大西洋还是从河流中
from both the Atlantic and the rivers.
流入地中海的水量就会减少
An event of this magnitude would have to have been global, not local.
这一现象的广度是世界级的 而非局部级别
However, this idea was proved wrong pretty quickly.
然而 这一假说很快就被证明是错误的
Soon after the Salt Giant was discovered,
巨盐矿被发现后不久
researchers started studying oxygen isotopes and other geochemical data
研究人员就开始对全球沉积层和冰核中的
from sediment and ice cores around the world.
氧同位素和其他地理化学数据进行研究
Their data showed that the rest of the Earth
研究数据显示当时地球的其他地方在
wasn’t abnormally hot, cold, or dry during the crisis.
盐度危机时并没有异常炎热、严寒或干燥
Plus, they found that some of the salt was deposited
而且他们发现一些盐量在
before any changes in sea level.
海平面变化前就已经沉积
So there didn’t seem to be a cooling event
因此 当时并没有发生明显的降温现象
that was big enough to turn off the flow of water.
足以导致水源被切断
That ruled out the first hypothesis.
第一种假说由此被排除
The second idea was that tectonic events had somehow
第二种假说认为板块运动以某种方式
blocked the Mediterranean off from the Atlantic,
阻断了地中海和大西洋的连接
and cut off the water flow.
因而也阻断了水流
Some researchers thought that shifting ocean crusts slowly blocked off the waterway
一些研究人员认为海洋板块的升降运动
between the Atlantic and the Mediterranean.
缓慢地阻断了大西洋与地中海间的水路
As the water left behind in the deep basin evaporated,
随着留在地中海盆地中的水分被蒸发
it became saltier and saltier,
海水变得越来越咸
depositing layers of salt as it dried.
盐类沉积层也越来越厚
And this explanation was *almost* right.
这种解释“几乎”正确
Other scientists thought that it might have been a combination of shifting crusts
另一些科学家则认为 可能是板块运动和
and climate change that made the Mediterranean dry up.
气候变化的共同作用导致了地中海的干涸
This was the third hypothesis.
这就是第三种假说
According to this model, the crust under the Strait of Gibraltar rose up over time,
根据这一模型 直布罗陀海峡下的地壳不断隆起
reducing the flow of water from the Atlantic.
使得大西洋流入的海水减少
Then, because of changes in regional climate,
接着 由于地区性气候的变化
like periods of less rain and higher temperatures
比如降水减少 气温上升
the amount of freshwater that made it into the Mediterranean varied.
进入地中海的淡水量也发生变化
So by this thinking, the MSC didn’t happen all at once.
根据这一设想 盐度危机并非一夜间发生
Instead, water levels started to drop after the strait closed,
相反 当海峡关闭后 水平面开始下降
and then fluctuated according to changes in the climate.
并随着气候的变化不断波动
And this hypothesis ended up being … pretty much right!
这一假说最终被认为 相当准确
Or at least close to it.
至少 几近准确
As geologists began collecting evidence to test these hypotheses,
为了验证这些假说 地理学家们开始收集证据
they eventually found that the MSC was indeed caused by changes in Earth’s crust,
他们最终发现 盐度危机确实是由地壳运动引发
but those shifts actually happened repeatedly, not just in one fell swoop.
只不过这类运动多次发生 并非只有一次
For example, in sediments near the Nile,
例如 在尼罗河附近的沉积层中
geologists found evidence of repeated erosion events,
地理学家找到证据表明侵蚀活动多次发生
not just a single big erosion.
而并非仅有一次大规模的侵蚀活动
This meant that the water level dropped,
也就是说 当海平面下降一次
created a new shoreline for a bit,
就会形成一个新的海岸线
and then dropped again a few more times.
之后 海平面还有多次下降
Some researchers estimate that there were 16 climate cycles
一些研究人员估计 在盐度危机开始之初
just in the beginning of the MSC.
曾经发生过16次气候循环
And these changes also correlated pretty closely with
另外 这些沉积层的变化与
what we know about climate cycles.
我们了解的气候循环的情况 有密切的关联
During periods of decreasing sea level,
在海平面下降的时期
the position and angle of the Earth changed with respect to the Sun,
地球的位置与角度跟随太阳而改变
so there were periods of lower solar energy,
所以有的时期太阳能量较低
and others of higher solar energy,
而有时太阳能量很高
which increased evaporation rates in the Mediterranean.
使得地中海海水的蒸发量增加
At the same time, an actively folding and uplifting tectonic belt
同时 地质构造板块频繁的折叠和上升
caused water input to decrease.
也导致流入的水量减少
Researchers were able to use chemical, and even magnetic signatures in the sediments
研究人员利用这一时期沉积层的化学性质
laid down during this time to estimate how long the MSC lasted.
甚至磁性来估计盐度危机持续的时间
And the data suggest that it went on for over 600,000 years,
数据显示它共持续了60万年
with the very driest period occurring about 5.6 million years ago!
其中最干燥的时期发生在560万年前!
At the height of the MSC, external water sources were completely cut off,
在盐度危机高峰期 外部水源被完全阻断
and most of the water left behind in the Mediterranean basin was evaporating.
留在地中海盆地中的水也几乎蒸发殆尽
Geologists think the water level dropped by a few hundred meters
地理学家认为水平面下降了数百米
the length of multiple American football fields.
是橄榄球场长度的数倍
And the water that was left was supersaturated,
剩余的海水盐分已过度饱和
so the salt continued to precipitate out at the bottom of the Sea.
导致盐分不断析出并沉淀在海底
The longer there was salty water that could precipitate out salt,
海水析出盐分的时间持续得越久
the thicker the final deposits became.
最终的沉积层就越厚
And the salt giant is possibly up to 3 kilometers thick,
巨盐矿的厚度可能高达3公里
which means that the sea was extremely salty
说明在长达成千上万年的盐度危机时期
for the hundreds of thousands of years during the MSC.
海水的咸度都异常高
And this, of course, had enormous effects
而这显然对生活在地中海里以及
on living things in and around the Mediterranean.
地中海周围的生物产生了巨大影响
Back then, life in the sea was dramatically different.
那时 海洋中的生存环境与现在截然不同
Today the Mediterranean Sea is home to thousands of marine species
如今的地中海是上千种海洋生物的家园
and is famous for its crystal blue water.
并以清澈透明的蔚蓝海水闻名
But when the sea almost dried up completely, it became uninhabitable.
但当海水几乎干涸时 它不再适合居住
Almost nothing could live there.
那里几乎没有生命
Most of the animals and plants that lived in the Mediterranean before the MSC
盐度危机前生活在地中海的动植物
either migrated away or died
由于海水变得又咸又浅
because the water was too salty and too shallow.
而要么迁徙别处 要么只能死亡
Some marine paleontologists think
一些海洋古生物学家认为
that no true marine organism was able to survive,
没有海洋生物能够存活下来
and the evidence for that is pretty good.
相关的证据显示的确如此
For one thing, the sediments that were deposited during this period weren’t disturbed, which
因为 这一时期的沉积层很完整
suggests that there were no burrowing creatures living there.
这表明没有任何穴居动物生存于此
And even now, there are hardly any deep sea animals
甚至到现在 都很难找到专属于
that are unique to the Mediterranean,
地中海的独特深海动物
because all of them died during the MSC.
因为 它们在盐度危机中就已灭绝
Some shelled creatures, like gastropods, might have survived,
一些腹足纲之类的带壳动物可能会生存下来
though they weren’t exactly thriving.
但远谈不上生机勃勃
Sediment cores showed that small populations
沉积层核心显示有一小部分腹足动物
may have eked out a living in isolated pockets.
可能曾在孤立的小洞中勉强生存
But the disappearance of the sea wasn’t all bad news for living things;
不过 海水消失对于生物也不只有坏处
the lower water levels were also an opportunity for some creatures to flourish.
降低的海平面也给了一些生物兴盛的机会
The distribution of fossils of now-extinct megafauna
从早已灭绝的巨型动物的化石分布来看
suggests that there was once a land bridge between the mainland and several Mediterranean islands,
大陆与地中海上的一些小岛 如撒丁岛
like Sardinia and Corsica, that has now disappeared.
和科西嘉岛曾有大陆桥相连 但现已消失
This allowed hippos, elephants, and other megafauna
大陆桥使犀牛 大象以及其它巨型动物
from Africa to walk and swim across the Mediterranean.
能够从非洲以走或游的方式穿越地中海
And we know that it wasn’t just megafauna that took advantage of
我们知道并非只有巨型动物
the crisis to move around.
利用盐度危机进行了迁徙
This seems to be when the ancestors of our giant friend, Nuralagus,
我们的大朋友兔王的祖先似乎
left the European mainland for Minorca.
也在这一时期从欧洲大陆来到梅诺卡岛
Paleontologists have found other giant fauna, like dormice and hamsters,
在一些自从危机结束后再无连接的岛屿上
on islands that haven’t been connected to each other
如马耳他和西西里 古生物学家还发现了
since the MSC, like Malta and Sicily.
睡鼠、仓鼠等动物的的巨型版
This wasn’t the first time that animals made a long journey to lands around the sea
这并非动物们第一次向分布在海洋中的陆地进行迁徙
it was just one of several migration events during the late Miocene.
它仅是发生在中新世的数次迁徙运动之一
The remnants of these migrations are found in the
迁徙的痕迹就体现在
fossilized remains of the hippos and elephants that lived there.
曾生活在那里的犀牛和大象的化石中
But when the water rose back up at the end of the MSC and land bridges disappeared,
但当盐度危机末期水面上升 大陆桥消失
the populations were isolated from each other, and from northern Africa.
动物就被隔绝在各自的岛上 与北非分开
That isolation led to small versions of large animals, or insular dwarfism,
隔绝导致大型动物体型缩小 或岛屿侏儒化
and large versions of small animals, or insular gigantism,
及小型动物体型变大 或岛屿巨型化
on islands around the Mediterranean.
两种现象在地中海岛屿上均有发生
Which solves the mystery of how Nuralagus got to Minorca
这也解释了为何兔王会来到梅诺卡
and why it ended up being so big.
以及体型最终如此巨大的原因
The Mediterranean Sea is back again, of course,
当然 地中海最终再次出现
so obviously the water returned at some point.
很明显 海水在某个时期又回来了
Models of the ocean crust suggest that the Strait of Gibraltar opened up
海底地壳模型显示 因板块再次升降以及
as the tectonic plates shifted again and sediments eroded,
沉积层的侵蚀 直布罗陀海峡重新打开
lowering the barrier between the Atlantic and Mediterranean,
大西洋和地中海间的阻隔降低
letting water flow through the Strait, and into the basin.
海水能够通过海峡流入地中海盆地
But just like the arguments about how the MSC started,
不过 就像争论盐度危机如何开始一样
there was a lot of debate about how it ended, too.
对于它是如何结束的 也有许多争论
At first, some scientists thought that it was replenished by a giant waterfall
一开始 部分科学家认为 重新涌入地中海的海水 会形成巨型的瀑布
cascading into the Mediterranean, with water pouring so fast that it filled up in only a few months.
瀑布倾泻得非常急 几个月就把地中海注满了
They even found sediment deposits that
他们甚至还在沉淀物中找到了
suggested a rapid flooding event occurred.
洪水曾迅猛地发生过的证据
And while that sounds amazing, it looks like it’s not true
尽管听起来很神奇 但看来并非事实
well at least, not the waterfall part.
至少瀑布的部分并非事实
More recently, other geologists using seismic data discovered
最近 另一些地理学家通过研究地震数据
that the slope between the Atlantic and the Mediterranean
发现大西洋与地中海间的倾斜角度
wasn’t steep enough for there to have been a waterfall.
并没有陡峭到足以产生瀑布
Instead, what re-filled the sea was probably more like a river.
相反 新涌入地中海的海水 更可能是形成河流
The basin did fill up quickly, though;
不过水确实注入得非常迅猛
recent estimates say it only took around 2 years to end the MSC,
近期的估算显示 赞克尔期大洪水
during an event sometimes called the Zanclean Flood.
可能只用了两年就终结了盐度危机
But that doesn’t mean this story is over.
不过故事还没有结束
The plates of the Earth are always shifting,
地球板块运动从未停止
and if the perfect storm of plate movement and climate change repeated itself,
如果 板块运动和气候变化反复同时发生
it could conceivably happen again.
那么 盐度危机可能会再次出现
Scientists are still finding more evidence of the MSC,
科学家仍然在从小型象和兔王的化石
from those fossilized mini-elephants, to Nuralagus,
和陆地及地中海底的盐晶中
to salt crystals found on land and under the Mediterranean Sea.
寻找更多关于盐度危机的证据
And while some events leave obvious marks on the planet’s surface,
有些事件会在地球表面留下明显印记
like mountains and craters,
比如山脉和陨石坑
there are others that you have to look harder to find traces of.
而另一些则需要努力探寻才能追踪其遗迹
Even though the MSC shaped life in and around the Mediterranean
尽管盐度危机千万年以来影响了
for hundreds of thousands of years
地中海周边及海中的生物
its fingerprints lie mostly out of sight, buried beneath the waves.
但它仍隐迹于波涛之间 尚未浮出水面
But the fossils of those dwarf elephants and giant rabbits
不过 侏儒象和巨型兔的化石
let us see its effects,
还是使我们得以窥其一斑
and help remind us of that moment in geological time
并提醒我们 在某个地理时期
when the Mediterranean Sea disappeared.
地中海曾经消失不见
Hey!
嗨!
Love bingeing PBS shows?
喜欢尽情观看PBS的节目吗?
Well the PBS Video App is your home for amazing educational shows
PBS视频程序为您提供优秀的科普节目
ranging from science films from NOVA to concerts on Austin City Limits
内容从天文新星到奥斯汀音乐节的音乐会
to documentaries from Ken Burns and Frontline,
还有来自Ken Burns和《前线》的纪录片
all with no ads or algorithms.
全都不含广告 也没有定向推荐
Oh and Eons. We’re there too!
对了 还有《PBS史前》我们也在!
If you live in the United States,
如果您住在美国
check out the link in our description to start watching
可在任何时候 几乎任何设备上
anytime on nearly any device.
点击简介中的链接开始观看
Now, giant bunny kicks to this month’s Eontologists:
最后 巨兔的内容由栏目组的本月科普员贡献:
Patrick Seifert, Jake Hart, Jon Davison Ng,
Patrick Seifert Jake Hart Jon Davison Ng
Sean Dennis, Hollis, and Steve!
Sean Dennis Hollis以及Steve!
Pledge your support and become an Eonite
承诺给予支持 就能在patreon.com/eons
at patreon.com/eons!
成为本栏目的赞助者
And as always, thank you for joining me in the Konstantin Haase Studio.
一如既往 感谢收看Konstantin Haase工作室制作的栏目
Be sure to subscribe at youtube.com/eons.
请别忘了在油管点击订阅

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视频概述

介绍了地中海曾经干涸的时期及墨西拿盐度危机

听录译者

收集自网络

翻译译者

槛外观云

审核员

审核员SR

视频来源

https://www.youtube.com/watch?v=HooZ84rpovQ

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