想象一个冰封世界 Imagine a world frozen solid.
从南极到北极都银装素裹 Encased in ice from pole to pole.
这片冻土平原上没有任何生物 No life roams these frozen plains.
只有冰川在其间默默漂移 Only glaciers move across them.
这不是什么缺乏光照的遥远星球 This is not some distant planet starved of sunlight.
根据一个激进的理论 According to a radical theory,
这是六亿五千万年前的地球 this was earth, 650 million years ago.
没有人知道什么导致了这样灾难性的冰冻 No one knows what triggered this calamitous freeze.
但若灾难曾发生过 But if it happened once,
是否可能再次发生 could it happen again?
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翻译：奥特慢 Fiona DayDay 小小石头 校对：幽幽&傲骨 时间轴：玖月 后期&特效：丢丢丢 总监：丢丢丢
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科学新发现系列
雪地球
发挥想象 描绘一个最深刻的冰河世纪 Imagine the most profound ice age you can think of.
温度骤降 即便在赤道附近也是零度以下 Temperatures plummet to below zero even at the equator.
不久之后 冰雪会把整个地球都包裹住 Before long, ice encloses our entire planet.
研究表明这种现象可能发生过不止一次 Research suggests that this may have happened not once,
而是在地球上曾经发生过三次 But three times in our planet's past.
欢迎来到雪地球 Welcome to snowball earth.
毫无疑问 雪地球 A snowball earth is certainly
是我们可以设想到的 the most extreme climate change
地球所经历过的最极端的气候变化 we can conceive the earth has ever experienced!
如果今天全球冰封会怎样 What would happen if the world froze over today?
大量冰川从极地延伸而来 Massive glaciers creep from the poles,
一路摧毁一切 crushing everything in their path.
首先 加拿大人为了捕鱼 First of all the Canadians are gonna have to
不得不把冰洞挖得更深 dig much deeper holes when they go ice fishing.
接着 华盛顿 爱达荷 蒙大拿 Next the governors of Washington, Idaho, Montana,
北达科他 明尼苏达 密歇根 缅因州的州长们 North Dakota, Minnesota, Michigan and Maine
都将宣布进入联邦紧急状态 will probably declare federal emergencies.
城市停止运转 Cities grind to a halt.
电线坍塌 供水冻结 Power lines collapse and water supplies freeze.
汽车无法启动 Cars won't start.
道路交通被冰雪堵塞 Roads are cut off by ice.
建筑在积雪的重压下变形 崩塌 Buildings strain and crumble under deep drifts of snow.
所有的一切都被冰封 Everything is entombed.
我们脆弱的身体为了生存而努力挣扎 Our frail bodies struggle to survive.
我认为如果雪地球再次发生 I think human society would collapse
人类社会将被毁于一旦 if a snowball earth happened again.
海洋冰封 The oceans freeze over.
鱼类死亡 海洋生态系统崩溃 Fish die and marine ecosystems collapse.
人类的食物供给很快被耗尽 Our food supply becomes exhausted.
所有幸存的人类都将遁入冰冷的地狱 Any surviving humans are trapped in an icy hell.
人类大量灭绝 We'd have a mass die of humans simply because
皆因无法在此条件下种植充足的食物 we could not grow enough food under these conditions.
虽然看起来令人震惊 Incredible though it may seem,
但地球很可能被完全冻结 the earth may have frozen over completely.
科学家正在意想不到的地方寻找线索 Scientists are finding clues in unexpected places.
故事始于一个谜 The story begins with a mystery.
在澳洲南部干旱的费林德斯山脉 In the arid Flinders Ranges in Southern Australia,
古代岩石层夹杂着非同寻常的岩石 layers of ancient rock hold unusual stones.
这些石头皆非本地原产 These stones are foreign to the area.
它们被称为"坠石" They are known as "dropstones".
坠石嵌入六亿五千万年前形成的 The dropstones are embedded in an ancient sedimentary seafloor
古代沉积岩层海底 that formed around 650 million years ago.
蒂姆·儒伯 Tim Raub,
加州理工学院地质学家 a geologist at the Californian Institute of Technology,
致力于费林德斯山脉的坠石搜寻 hunts for these dropstones at the Flinders Range.
蒂姆·儒伯博士 加州理工学院
这是一份坠石样本 This is an example of a dropstone,
一块古老的岩石 a piece of ancient rock
坠入古老的海底泥层 that was dropped into the ancient mud on the sea bottom.
这些坠石 These dropstones are visibly different
与周围的沉积岩床明显不同 from the sedimentary bedrock around them.
一定是某种强大的力量把它们带到这里 Something powerful must have carried them here
但是什么力量呢 but what?
丹·施拉格 Dan Schrag,
哈佛大学地球与行星科学系教授 professor of earth and planetary sciences at Harvard University,
认为这种力量来自冰川 believes the answer is glaciers.
我们在这里制造出了冰块 We actually have ice cubes here
并把砂砾掺入其中 that we've made with pieces of sand and gravel in them,
丹·施拉格教授 哈佛大学
使这些冰块模拟出冰川 so these ice cubes are like the glaciers
从陆地上携卷起岩石的效果 that are taking rocks from the land
当我们把它们放入水中 and then when we put them in the water,
冰块就会融化 they'll actually melt
沙砾则会沉入水底 and the sand and gravel will fall to the bottom,
就像海底的坠石 just like the dropstones on the ocean floor.
在某段时期 该区域被厚厚的冰层覆盖 These dropstones are evidence that at some point,
这些坠石就是证据 this area was covered in a thick layer of ice.
但很难解释的是 But it's difficult to explain
冰雪是如何能够覆盖在南澳太阳炙烤的山脉 how ice could have covered the sun-baked mountains of Southern Australia.
除非大陆本身曾处于一个截然不同的地区 Unless the continent itself was in a very different place.
大陆并非静止不动 The continents haven't always been where they are now.
由于板块的漂移 They move very slowly across the earth
它们在地球表面缓慢移动 due to the movement of tectonic plates.
大约六亿五千万年前 650 million years ago,
弗林德斯坠石在此着陆 around the time the Flinders dropstones landed here,
大陆地貌变得截然不同 the continents were positioned very differently.
因为坠石在冰下形成 Since the dropstones formed under ice,
也许澳大利亚曾位于靠近极地的 perhaps Australia sat nearer to the poles
低温地带 where temperatures were lower.
为了定位远古时期大陆的位置 To locate the position of a continent in the distant past,
科学家们对岩石进行了磁特性研究 scientists study the magnetic identity of rocks.
某些沉积岩含有磁性粒子 Certain sedimentary rocks contain magnetic particles.
在岩石形成的过程中 这些铁离子 When the rocks form, these iron particles
与地磁场走向一致 line up with the earth's magnetic field.
在极地附近 它们排成直角 Near the poles, they align at right angles
垂直穿过沉积岩层 to the sedimentary layers.
在赤道附近 And around the equator,
则与沉积岩层保持平行 they align parallel to the layers.
即使岩石移动 Even if the rock moves,
这些磁性粒子独特的排列结构 the distinctive configuration of these magnetic particles
也能保持不变 remains the same
这就是岩石的"地质指纹" and provides a kind of 'geological fingerprint' of the rock.
加州理工学院帕萨迪纳实验室的乔·克茨芬克教授 Professor Joe Kirschvink at Caltech, Pasadena,
对磁力深深着迷 is fascinated by magnetism.
磁力充满魔力 Magnetism is magic.
我甚至用一块磁石的名字为我的长子取名 I've even named my eldest child after a magnet.
约瑟夫·克茨芬克教授 加州理工学院
我热爱磁力 So I enjoy magnetism.
克茨芬克及其团队成员 Kirschvink and his team analysed
对坠石周围六亿五千万年前成形的岩石进行分析 the 650-million-year-old rock surrounding the dropstones.
结果出乎意料 The results were unexpected.
澳洲该地区与赤道的夹角不到五度 That part of Australia was within 5 degrees of the equator.
而它又是最不可能 And it just was the most weird place
会有冰川存在的地区 to expect a glacier.
但克茨芬克非常肯定 But Kirschvink had to be sure that
这种古老岩石仍保持着最初的磁性特征 this ancient rock still held its original magnetic signature.
如果岩石成形后遇高温受热 If the rock heated up after it formed,
那么它的原生磁性会改变 its native magnetism would have changed.
回到弗林德斯山脉 Back at Flinders Range,
克茨芬克的团队发现了 Kirschvink's team uncovered
具有条纹的沉积岩就是很好的证明 clearly striped sedintary rock that provided proof.
看 成千上万的泥层 Here. Tens of thousands of layers of mud
从六亿三千五百万年前形成的冰原边的 grew one at a time upward and upward in a glacial lake
冰川湖里一层一层不断向上生长 at the edge of a 635-million-year-old ice sheet.
当岩石形成 When this rock formed,
沉积层会构造出独特的水平线 layers of sediment built up in distinctive horizontal lines.
通过比较沉积物质的排列方向 By comparing the direction of the layers of sediment
和磁力线的方向 with the direction of the lines of magnetism,
克茨芬克可以确定 Kirschvink could determine
岩石磁场特性是否发生了变化 whether the rock's magnetic signature had changed.
我们可以用一块橡皮来解释磁场作用的过程 We can explain the process of magnetism with a simple eraser.
如果岩石在赤道形成 If the rocks formed on the equator
并且很早就受到磁场作用 and gained a magnetism very early
可以预计磁场方向和岩层是平行的 we would expect the magnetic direction to be parallel to the bedding
基本就像这样 very precisely like this.
然后 因为岩石是松软的 And then since the rocks are soft
如果受到地质学中所谓的挤压或者变形 if they get squeezed or deformed geologically
可以预见它们会像这样偏转 you would expect them to rotate like this
磁性也会随着岩石而偏转 and the magnetism would shift with the bedding.
另一种情况 On the other hand
如果岩石先受到挤压变形 if the rock had been squeezed and deformed first
然后才像这样受到磁力线的作用 and then gained the line of magnetism like this,
我们会看到它们相对于现在的岩层是弯曲的 we would see them warped relative to the bedding today.
如果岩石仍然维持最初的磁场方向 If the rock still had its original magnetic orientation,
那么磁力线就会沿着沉积物质走向排列 the lines of magnetism would follow the lines of sediment.
但是如果沉积岩层方向有所改变 But if its orientation had changed,
那么磁力线就会穿过沉积岩层 the magnetism would cut through the sedimentary layers.
儒伯往地层打钻 Raub drills into the formation
对这种有规律条纹的岩石内部进行取样 to retrieve solid cores of the rhythmic rocks.
回到实验室 Back in the lab,
团队成员 the team analyses samples of rock
利用定制的高灵敏度磁力仪对岩石样本进行了分析 using a custom-built, hypersensitive magnetometer.
磁力仪用于检测岩石中 This magnetometer measured the orientation
磁性粒子的排列方向 of the magnetic particles in the rock.
它证实了磁性粒子 It confirms that the particles
与岩层排列一致 were aligned with the rock layers.
克茨芬克对此感到吃惊 Kirschvink was astonished.
坦白说 一开始我看到这样的研究结果 Quite frankly when I saw the original study
完全不相信 I didn't believe it.
我们看到的实际上是这样的 What in fact we see is that they're like this
而当岩石弯曲磁力线也弯曲 and as the rock was warped the magnetism warped.
这就证明了 That proves conclusively
在岩石固化之前 磁性就已经形成了 the magnetism formed before the rock was solidified.
这一发现为冰成岩在赤道附近的形成 This discovery seems to provide irrefutable evidence that
提供了确凿的证据 the glacial rocks formed close to the equator.
保罗·霍夫曼 哈佛大学地质学教授 Paul Hoffman, professor of geology at Harvard University,
对此很感兴趣 was intrigued.
如果温度最高的赤道地区附近 So if there were glaciers close to the equator
保罗·霍夫曼 哈佛大学
曾经存在冰川 where the temperature was warmest,
那么就能假设 在温度更低的 one has to assume that there was also ice
高纬度地区也曾经被冰雪覆盖 in higher latitudes where the temperatures were colder.
六亿五千万年前 650 million years ago,
澳洲位于赤道附近 Australia sat near the equator.
这一证据还可以说明 And yet evidence suggests
干旱的岩石曾经埋在冰雪之下 that its arid rocks lay buried beneath ice.
如果赤道地区曾被冰雪覆盖 And if there was ice at the equator,
那么全球也都会被冰雪覆盖 there would have been ice all over the globe.
这些坠石促使一种激进理论的产生 These dropstones became the catalyst for a radical theory:
雪地球 snowball earth.
这个理论即是最极端条件的冰期 This is a theory about the most extreme ice age imaginable.
如果它曾经发生过 And if it happened before,
也许会再次发生 it could happen again.
雪地球
我们的地球经历过很多 Our world has been through many periods
极端气候变化的时期 of extreme climate change.
但一些科学家已经提出 But some scientists have proposed
六亿五千万年前 that 650 million years ago,
地球可能处于完全冰封的状态 the earth may have frozen over completely.
这种激进的假说产生了一个关键问题 This radical hypothesis raises one crucial question:
它是怎么发生的 how could it have happened?
克茨芬克认为范围如此之广的冰封 Kirschvink proposes that the giant freeze
是因为同一机制导致的 was triggered by the same mechanism
这也是今天全球变暖的原因 that lies behind today's global warming:
即 温室效应 the greenhouse effect.
只不过在六亿五千万年前 Except 650 million years ago,
其效果截然相反 it worked in reverse.
大气中的温室气体 Greenhouse gases in our atmosphere
就像是保温层 act like an insulating blanket,
阻隔太阳的热量 trapping the sun's energy
使地球维持温度适中的状态 to keep earth's temperatures mild.
当雪球时期降临 科学家猜想 When the snowball began, scientists suspect that
这些重要的气体含量急剧下降 levels of these vital gases fell dramatically.
地球的大气层可能充满了 The earth's atmosphere might have been filled with
蒂姆·儒伯博士 加州理工学院
甲烷和二氧化碳 methane and carbon dioxide
地球为了保持温度 and the earth became addicted
必须依赖二氧化碳和甲烷 to this high level carbon dioxide and methane in order to keep its temperature.
如果因为某种未知事件 Then if some unknown event crashed
使得二氧化碳脱离大气层 the carbon dioxide out of the atmosphere
地球可能失控并进入雪地球时期 earth might have run away into a snowballed earth.
如果将足量的二氧化碳从大气层中抽离 If enough carbon dioxide had been pulled out of the atmosphere,
反温室效应就会 an anti-greenhouse effect would have
使地球深度冰封 plunged the earth into a deep freeze.
但是该理论可行的前提是 But this theory is only possible
找到能使空气中的二氧化碳大幅度降低的机制 if there's a mechanism that could pull all the co2 out of the air.
事实上 大自然对硅酸盐风化作用 In fact, carbon dioxide is removed all the time
一直在消耗空气中的二氧化碳 through a process called silicate weathering.
风化是一个地质名词 Weathering is a geological term
是指岩石受自然环境的影响逐渐分解的过程 for the decomposition of rocks under the influence of the weather.
它能将岩石转变为土壤 It's a process that converts solid rock into soil.
这种现象对于气候变化的重要之处在于 Now its importance for the climate
它不断消耗大气中的二氧化碳 is that weathering consumes carbon dioxide,
而二氧化碳是温室气体的主要组成部分 which is a major greenhouse gas in the atmosphere.
二氧化碳与空气中的水蒸气相互作用 Carbon dioxide reacts with water vapour in the atmosphere
形成碳酸雨 to form carbonic acid rain.
这种酸雨进而溶解地上的石灰岩 石灰岩 一种含大量碳酸钙的沉积岩 This acidic rain weathers limestone on land
将腐蚀下来的沉积物带入大海 and carries away the eroded sediment to the sea.
沉积物聚积于海底 Here it builds up,
最终在海床上形成了石灰岩 eventually forming limestone on the seafloor.
石灰岩出现在这个地方 So the presence of the limestone
证明了风化现象的存在 is the evidence that weathering is occurring.
随着锁在石灰岩里二氧化碳增多 The more carbon dioxide gets locked away in limestone,
地球就越冷 the cooler the earth becomes.
不过 既然这一过程长期存在 But if this is happening all the time,
那么必有某种事物加快了这一进程 something must have amplified the process
使得地球被整体冰封起来 for the whole world to have frozen over.
证据再一次与当时的大陆位置分布有关 Again, clues lie in the position of the continents.
持续的地壳板块构造运动 The movement of tectonic plates continually
使得陆地在全球范围内来回移动 shifts the continents around the globe.
今日 大多数陆地都位于 Today, a lot of the continents
较高的纬度位置 are located in higher latitudes.
如果地球温度下降 If the earth cools,
那么两极附近的陆地会率先结冰 the continents near the poles ice over.
而这些冰会保护下层的岩石 The ice prevents the rocks beneath
免受碳酸雨的侵蚀影响 from being weathered by carbonic acid rain.
这就保证了风化循环处于平衡之中 This means that the weathering cycle is kept in balance.
锁在石灰岩中的二氧化碳减少 With less carbon dioxide locked away
大气里的二氧化碳增多 in limestone rock and more in the atmosphere,
地球的温度就会再度上升 the planet warms.
科学家们发现 Scientists have worked out
六亿五千万年前 that 650 million years ago,
陆地都聚集在多水温暖的赤道附近 the continents were clustered around the equator, where it's warm and wet.
所以 全球的风化速度也会更快一些 Consequently, the global rate of weathering would have been higher.
在"雪地球"时期 我们怀疑 During the snowball earth we suspect that
由于太多数大陆聚集在赤道附近 there were many more continents at the equator
丹·施拉格教授 哈佛大学
最终的后果便是 and this would actually lead to a situation
地球将更容易进入全球冰川期 that would make the planet vulnerable to a global glaciations.
地球降温时 As the earth cooled,
两极开始出现冰层 ice formed at the poles.
可是由于高纬度并没有陆地 But because there were no continents in the higher latitudes,
冰层更多的是聚集在海面上 ice accumulated on sea rather than on land.
没有陆地能够对风化进行调控 There was nothing to regulate the weathering.
持续的降温便无法抵挡了 The cooling continued unchecked.
于是整个世界越来越冷 And the world got colder and colder.
这种失控的情形确实有可能 This runaway scenario is certainly plausible.
即便极端的风化作用可能造成冰期 But although extreme weathering could be behind an ice age,
这也不能说明为何冰层 it doesn't explain how the earth
能彻底覆盖整个地球 could have iced over completely.
阿德莱德大学的地质学家伽林·霍尔沃森 Geologist Galen Halverson from Adelaide University
一直致力于研究"雪地球"的诱因 studies triggers of the snowball.
"雪地球"研究最难的一部分 One of the hardest parts about
就是搞清楚这个时期到底是如何开始的 understanding the snowball is really how it began.
伽林·霍尔沃森博士 阿德莱德大学
我们认为它定是从一场正常的冰川作用开始的 We think that it must have began like a normal glaciation.
一般来说 生物会帮助地球平衡气候 Normally, living things help to regulate the earth's climate
这是通过二氧化碳浓度的微调来实现的 by maintaining the delicate balance of carbon dioxide.
植物消耗二氧化碳 Plants consume carbon dioxide.
动物产出 Animals produce it.
消耗者和提供者 These consumers and producers
一起调节气候 help to regulate the climate,
确保地球不会太热 也不会太冷 ensuring that the earth is neither too hot nor too cold.
如果大气层里有过多的二氧化碳 If there's more carbon dioxide in the atmosphere,
天气就会变热 it gets warmer.
这能帮助植物更快地生长 This causes plants to grow faster
从而从空气中吸取更多的二氧化碳 which in turn draws out more co2 from the air.
气候太热时这就是一种反馈调控 So that is a feedback against it getting too warm.
反之 如果天气太冷了 And in reverse if it starts getting too cold
生物层就会相应地 then the biosphere responds
减慢二氧化碳的消耗 by not drying down as much co2
这样二氧化碳含量就会慢慢回升 and that allows co2 to go back up
这就如同地球的缓冲系统 so there's a sort of buffer in the form of life on earth
防止气温太低或者太高 that prevents temperatures from getting too cold or from getting too hot.
不过 回到六亿五千万年前 But rewind 650 million years
则是另外一副截然不同的局面 and witness a very different story.
当时陆地上的生命还在进化的初级阶段 Life on land was in its early stages of evolution.
大多数生物体还在海洋中 Most living things were in the oceans.
这种半成熟的生物层还无法阻止 This half-formed biosphere could not prevent the earth
地球往极端气候发展 from swinging to wild extremes of temperature.
大量的单细胞生物蓝藻 Colonies of single-celled organisms called cyanobacteria
首先进化出了光合作用 were the first to photosynthesize.
它们从水中摄取二氧化碳 They pulled carbon dioxide from the surrounding water
经过反应沉析出碳酸钙后 to precipitate calcium carbonate
用以建造这些圆顶状的岩石 and they used this to make dome-like structures of rock.
地质学家吉姆·戈林是研究这些早期生物的专家 Geologist Jim Gehling is an expert on these early life forms.
六亿五千万年前 Temperatures were dropping at this time,
气温急剧下降 650 million years ago,
詹姆斯·戈林 南澳博物馆
很有可能是因为二氧化碳 for the very good reason that carbon dioxide,
这种主要温室气体 the principle greenhouse gas,
从大气中被抽出来 was being taken out of the atmosphere
锁在了海床上而造成的 and locked away on the seafloor.
今天 我们仍旧可以在叠层石礁上 This trapped carbon dioxide can still be seen today
看到被锁住的二氧化碳 in stromatolite reefs.
这些其实是固体形式的二氧化碳 This is actually solid carbon dioxide,
千万年后 我依旧可以从 and I can release that carbon dioxide
这些岩石里将它们释放出来 after all those hundreds of millions of years,
当我把这瓶弱酸倒在石礁上时 when I put this weak acid on the rock.
你可以看见它被腐蚀了 And there you see it's erupt
白色二氧化碳的泡泡不断从岩石冒出 as white bubbles of carbon dioxide spring out of the rock,
重新回到大气层里 go back into the atmosphere,
扮演它们温室气体的角色 to take up their role all over again as greenhouse gases.
蓝藻吸收的二氧化碳越多 The more carbon dioxide the cyanobacteria locked away,
地球就越冷 the cooler earth became.
我们的星球的温度急转直下 Our planet was hurtling towards a deep freeze
从此被冰封了几百万年 that would last for millions of years.
雪地球
六亿五千万年前 650 million years ago
地球温度骤降 the earth's temperature plummeted.
大片冰原纵横于星球之上 Huge sheets of ice spread across the planet.
事实上 它们吞没了绝大多数的海洋与陆地 Eventually, they engulfed most of the land and sea.
这已经不是普通的冰期了 This was no regular ice age.
冰期并无特别之处 Ice ages are nothing out of the ordinary.
每隔好几万年我们便会经历一次 We experience them every hundred thousand years or so.
它们的出现主要由于地球轨道的微小变化 They are mainly caused by small changes in the earth's orbit,
导致与太阳相对位置发生改变 which alter its position relative to the sun.
当我们的星球数年内没有充足的太阳辐射 When our planet receives less of the sun's energy over a number of years,
冰层便会从北半球开始形成 一路向下 ice forms high in the northern hemisphere and advances down.
两万一千年前的最后一次冰川时期 At the height of the last ice age 21,000 years ago,
冰层一度覆盖至纽约这个纬度 these icy sheets reached down as far as New York.
不过热带丛林依旧温暖 But the tropics stayed warm.
当时只有30%的地球被冰覆盖 Only about 30 percent of our planet froze.
但六亿五千万年前 But 650 million years ago,
有些科学家认为冰层持续推进 some scientists believe the ice kept coming,
最终 覆盖了整个地球 until eventually, most of the globe was covered.
是什么原因促使温度失控 不断下降呢 What could have caused this runaway cooling?
问题的答案 The answer must lie in
便是地球如何维持和失去太阳的能量 how our planet keeps or loses the sun's energy.
地球表面由陆地 开阔的海洋 The earth's surface is made up of land,
以及冰原组成 open ocean and ice.
这些表面或多或少都会反射阳光 These all reflect sunlight to a different degree.
一个表面可反射光线的多少 The amount of light a surface reflects
即为反射率 is known as its albedo.
幽深的海洋反射率较低 Deep, dark ocean has a low albedo,
因为它能吸收大量的阳光 since it absorbs a lot of sunlight.
而白雪和冰原则反射率很高 White snow and ice have a very high albedo,
它们更易将太阳辐射的能量反射回太空 since they reflect more of the sun's energy back into space.
蒂姆·儒伯向我们展示了 深色和浅色 Tim Raub demonstrates how dark and light colours
在阳光下如何升温 heat up under the sun.
这辆白车在阳光暴晒下 The temperature of a white car sitting in the sun
只有48.9摄氏度 is only 120 degrees.
蒂姆·儒伯博士 加州理工学院
同样的情况下黑车却达到了 The temperature of a black car sitting in the sun
62.2摄氏度 is 144 degrees.
黑车更易吸收阳光 The black car absorbed light;
而白车更易反射 the white car reflected it.
白色能反射更多的阳光 White reflects more sunlight,
保证了其所覆盖物品的温度更低 keeping whatever it's covering cooler.
地球上冰层越广 The more ice that covers the earth,
就会反射更多的日照能量 the more of the sun's energy reflects back into space
地球也会越来越冷 and the colder the planet becomes.
寒冷的条件会造就更多的冰层 This cooling leads to more ice forming,
进一步增加地球表面的反射率 which further increases the surface albedo.
这就是冰反射率反馈现象 This is known as ice-albedo feedback.
某些事件可能更是加速了 And something may have accelerated
这种持续降温的循环 this cycle of cooling even more.
新的研究调查表明 New research suggests that
海水在极低的温度下结冰时 when sea water freezes at very low temperatures,
它的结构可能发生改变 its composition changes
从而反射能力更强 and it can become more reflective.
在华盛顿大学的极地科学中心 At the University of Washington's Polar Science Center,
邦妮·莱特致力于研究冰与光线的关系 Bonnie Light studies the relationship between ice and light.
在冷藏室中 In the cold room,
她将盐水放在不同温度下进行冷冻 she freezes buckets of saltwater at different temperatures.
其中一桶放置于零下23.3摄氏度 One of the buckets is exposed to
即雪球时期地球所处的温度 snowball earth temperatures of minus 10 degrees.
这边表面的冰显然更白了 The surface of this ice becomes much whiter.
这一桶海水 Okay, so this bucket contains sea water
是放在零下15摄氏度的 that was frozen in a cold room
冷藏室进行冰冻的 at 5 degrees above zero Fahrenheit,
这桶模拟了现在地球上的 And we consider this a good laboratory analogue
邦妮·莱特博士 极地研究中心
海冰情况 for modern day sea ice on planet earth.
你能清楚的看到其表面 And you can see that the surface of it
呈现的是暗灰色 is kind of grey coloured, dull appearance.
这桶也有咸水 And this bucket also has salt water in it,
但是却放在了 although this salt water was frozen
零下23.3摄氏度的冷藏室进行冷冻 at about 10 degrees below zero Fahrenheit,
这桶模拟了当时雪球时期 and we consider the ice in this bucket
海冰的形成情况 to be a good analogue for sea ice on snowball earth,
因为这温度已经很低了 because it's very cold.
在雪球时期的温度下 At snowball earth temperatures,
海冰的构成发生了变化 the composition of the sea ice changes,
使得冰面由灰转白 turning its surface from grey to bright white.
你会发现在这桶冰上 这些颗粒已经 And you can see that these crystals, in this case,
厚厚地聚积在冻层表面 have started to collect at the surface of this cold ice.
我甚至可以将这些晶体刮开 And so I can kinda scratch away these crystals,
你会发现它们基本上就沉淀在 and you see that it's basically just a deposit
冻冰的表面上 on the surface of this cold ice.
在零下23.3摄氏度时 At minus ten degrees,
冰中的盐分子形成细小的晶粒 salt molecules in the ice begin form tiny crystals.
如果在显微镜下将它们分离开来 If you can isolate them under the microscope,
就像是 一颗颗宝石一样 um... they look like little gemstones.
真的非常漂亮 They're really quite beautiful.
这些亮闪闪的晶体对反射率影响极大 These bright crystals have a dramatic effect on albedo.
白色的表面能分散更多太阳的能量 The white surface scatters more of the sun's energy
将能量统统反射回太空 and reflects it back to the atmosphere,
使得温度进一步降低 causing temperatures to drop even further.
在二十世纪六十年代 In the 1960s,
前苏联气象分析员麦克海尔·布迪科 Soviet climate modeller Mikhail Budyko
演示了失控的冰反射率是如何 demonstrated how runaway ice-albedo
让地球降温以致完全冻结的 could cause a cooling earth to freeze completely.
正如许多同代人一样 Like many of his contemporaries,
布迪科也很担忧核冬天的影响 Budyko was worried about the affects of a nuclear winter.
核爆炸产生大片的烟尘云团 Nuclear explosions create clouds of smoke and dust,
会屏蔽太阳的能量 which block the sun's energy
并降低地球的温度 and lower the earth's temperature.
布迪科开发了一个数学模型 Budyko developed a mathematical model
来计算全球进入冰期的几率 to work out the odds of a global ice age.
他指出 如果地球的气候 He showed that if the earth's climate cooled enough
低至令低纬度结冰 for ice to form in the lower latitudes
那么冰反射率就会快速上升 then the ice albedo would rise at a faster rate.
一旦冰川延伸到了一定的纬度 And once the glaciers reached a certain latitude,
整个地球就会突然进入一个大雪球的状态 the earth would tip into a snowball-like state.
冰原带 冰川以任何方式 Somehow or the other the ice line, the glaciers,
延伸到大约30度的临界纬度时 reached some critical latitude around 30 degrees
而且一旦它延伸到这个纬度 很快 and once they hit that latitude very, very rapidly,
整个地球都会冰封 the earth would have been entombed in ice.
布迪科突破性的研究表明了这个雪球效应 Budyko's ground-breaking work showed how this snowballing effect
是如何在数十年内就将地球冰封 could create a totally frozen planet within just a few decades.
布迪科的研究极其重要 Budyko's work was extremely important
约瑟夫·克茨芬克教授 加州理工学院
它展示了地球是有可能 in demonstrating that it was possible
陷入气候灾难 that earth might slip into a climate catastrophe
即全球冰封 which was covered completely with ice.
在他之前无人认为这是可能的 It had not been recognized as a possibility before that.
如果地球完全被冰封 If the earth became entirely covered in ice,
那么它接受的几乎全部太阳的热量 nearly all the heat it received from the sun
都会被反射回太空 would be reflected back into space.
那么地球就将永久冰封 The planet would become locked in ice.
如果失控的降温将地球冰封 So if runaway freezing trapped the earth in ice,
那地球又是怎么摆脱冰封的呢 how did it ever escape?
Naked Science Snowball Earth
有科学家提出 在6亿5千万前年 Some scientists suggest that 650 million years ago,
我们的地球曾处于极端的冰河时代 our entire planet was locked in an extreme ice age.
"这是个非常特殊的事件 It was a unique event,
是由一系列的不可能发生的事件引发的结果" the result of a set of improbable triggers.
这是他们的想法 Or so they thought.
后来 在1997年有证据表明 Then, in 1997, evidence emerged that
冰河时期还不止发生过一次 it could have happened more than once.
这个证据就是南非 It came from glacial deposits in South Africa
超过两亿年的冰积层 that were over 2 billion years old.
古地磁的证据表明 Paleomagnetic evidence suggests that
这些是在赤道附近形成的 these formed near to the equator.
地理学家保罗·霍夫曼认为这可以证明 Geologist Paul Hoffman believes this is could be proof
有史以来 地球至少完全冻结过两次 that the earth froze over completely at least twice in its history.
最能证明22.2亿年前冰雪地球的 The best evidence for a snowball earth 2.22 billion years ago
保罗·霍夫曼 哈佛大学
就是南非的古地磁证据 is paleomagnetic evidence from South Africa.
那里有在赤道附近形成的 There are glacial tills there, boulder clays,
冰碛物和冰砾泥 that formed very close to the equator.
该发现表明 This discovery raised the possibility
雪地球可能并非单一事件 that the snowball wasn't a single event,
而是一种循环状态 but a recurring condition.
科学家们争相找出早期深层冻结的诱因 Scientists raced to find the trigger for this earlier deep freeze.
冷却时间和大氧化事件正好相同 The cooling appeared to coincide with the great oxidation event.
在海洋的深处 Deep in the ocean,
某些最古老的生命体 some of the oldest organisms on earth
进化出了光合作用的机能 evolved a mechanism called photosynthesis:
即利用太阳能把二氧化碳转变为氧气 the ability to convert carbon dioxide into oxygen using the sun's energy.
当这些光合作用的微生物兴盛起来后 As these photosynthesizing microbes thrived,
它们对地球的气候产生了深远的影响 they had a profound affect on the earth's climate.
20亿年前 Two billion years ago,
太阳能量不及现在 our sun was weaker.
我们的地球依靠温室气体 Our planet relied on greenhouse gases
比如二氧化碳和甲烷(沼气) like carbon dioxide and methane
来维持它的温和气候 to maintain its temperate climate.
但是光合作用消耗掉二氧化碳 But photosynthesis uses up carbon dioxide.
光合作用也产生氧气 这也破坏了甲烷 It also produces oxygen, which destroys methane.
这导致双重打击的一个结果 The result: a double-whammy.
两种重要的温室气体水平直线下降 Levels of both these vital greenhouse gases plummeted.
这是很危险的情况 You have a precarious situation.
约瑟夫·克茨芬克教授 加州理工学院
我们地球原是需要甲烷的温室星球 You have a planet that's greenhouse needs methane
却突然进化出了一个破坏沼气的小虫 and you suddenly evolve a bug that destroys the methane.
可能一种光合作用的细菌首次出现 Maybe the first bacteria that photosynthesised
破坏了大气中的二氧化碳和甲烷 crashed the carbon dioxide and methane from the atmosphere
圣马洛·劳尔斯 加州理工学院
引发了第一次雪地球的形成 and triggered the first snowball earth.
当制氧量飙升时 As oxygen production soared,
甲烷含量暴跌 methane levels tumbled.
失去了温室气体 With the loss of that greenhouse gas,
地球跌至深度冻结 the earth spiralled into a deep freeze.
这是一很骇人的结论 It's kind of a frightening conclusion
一种单细胞的变异小虫 that a single celled mutant bug
毁掉了整个行星的生态系统 destroyed an entire planetary ecosystem.
毁了 Destroyed it.
将其变成了一个大雪球长达 Turned it into a snowball for maybe
3千5百万到1亿年之久 35 to 100 million years.
现在有一些科学家认为 Some scientists now think that
我们的地球在历史上至少有 our planet has been encased in ice
分别的三次完全被冰封 on at least three separate occasions.
而且每一次情况都不一样 And each time, under different circumstances.
然而雪地球的情况带来一个大问题 But these snowball earth scenarios present a huge problem:
如果我们的地球被困在冰里 if our planet was trapped in ice,
它又是怎么摆脱的呢 how did it ever escape?
肯定有什么引起了全球大融冰 Something must have caused a global meltdown.
Naked Science Snowball Earth
大解冻的证据就在这里 Evidence of the thaw is right here.
在坠石的顶端 On top of the dropstones
有层红灰色的特殊岩石 sit layers of a peculiar reddish-grey rock.
这些岩石层在弗林德斯山脉和死亡谷绵延数里 These layers stretch for miles in the Flinders Range, Death Valley
有冰成岩的地方几乎都能看到它的踪影 and almost everywhere where the glacial rocks appear.
它们就是碳酸盐岩 These are carbonate rocks,
形成于温暖的浅海 which form in warm, shallow seas.
但在这里 它们却出现在冰积层的上部 But here, they appear right on top of the glacial deposits.
我这有个样品能清楚看到 So here's a sample that actually
雪地球事件的终结痕迹 shows the end of the snowball event.
这就是经过冰筏作用的石头 So that's an ice-rafted stone
它是从冰山上掉落下来的 that dropped out of an iceberg
这些小谷粒状的石头也是从冰山上掉落的 and these are little grains that also fell out of an iceberg,
那么在这之上 and immediately on top of that
没有任何的层缺直接形成了碳酸盐岩帽 without any break in sedimentation is Cap Carbonate,
直接在海洋外沉淀 it's precipitating directly out of the ocean
并且在海底累积起来 and accumulating on the seafloor.
这种相同的关联在全世界都能看到 And exactly the same relationship is seen all over the world.
它们的存在就是温度骤增的证明 Their presence is evidence of a sudden and drastic temperature increase.
只有一样东西会引发这种情况 Only one thing could have triggered this:
大量温室气体的注入 a huge injection of greenhouse gases
比如二氧化碳 such as carbon dioxide.
为了融化掉雪地球 In order to melt snowball earth,
二氧化碳的浓度 concentrations of carbon dioxide
要比今日高出350倍 had to be around 350 times higher than they are today.
但如果整个地球都被厚厚的冰层覆盖 But if the whole planet was encased in a thick layer of ice:
二氧化碳又是从哪来的呢 where did the carbon dioxide come from?
加州理工的约瑟夫·克茨芬克教授灵光一现 Caltech professor Joe Kirschvink had a revelation.
我大半夜里醒来 大喊道 I woke up in the middle of the night and said:
"啊 一定是这样的" "Ah, that's gotta be it!"
我顿时就想到了那些高耸入天的火山 It just dawned on me that these sub aerial volcanoes
像位于黄石公园和阿留申群岛里的 like in the Aleutians, in Yellowstone...
这些火山还在 并向空中喷发二氧化碳 These volcanoes sit and they spew Co2 into the air.
即使在冰层底下 Even beneath the ice,
火山也会继续释放大量的二氧化碳 volcanoes would have continued to release immense volumes of carbon dioxide.
因为地球的其他地方还是被冰封着 With the rest of the planet still ice-locked,
所以就没有办法从大气层种消除二氧化碳 there would have been no mechanism to remove it from the atmosphere.
经过了数百万年 温室气体的水平慢慢提高 Over millions of years, levels of this greenhouse gas would have built up,
最终产生了足够的热量抑制了冰反射 eventually producing enough warming to off-set the ice albedo.
冰融化了 The ice melted,
导致全球气温急速上升 sending global temperatures spiralling upwards.
当融冰的水蒸发时 As this melted ice water evaporated,
大气层也变得潮湿 产生了猛烈的降水 it swelled the atmosphere with moisture, creating torrential rainfall.
二氧化碳在大气中酸化了雨 Carbon dioxide in the atmosphere acidified the rain.
酸性的倾盆大雨腐蚀了石灰岩 Acidic downpours rapidly eroded limestone,
把沉淀物冲刷进了海洋里 washing sediment down into the oceans.
在这里 碳酸盐的沉淀层累积在海底 Here, layers of carbonate sediment accumulated on the seafloor
形成了碳酸盐岩 to become carbonate rock.
丹·施拉格为我们演示整个过程 Dan Schrag demonstrates what could have happened.
丹·施拉格 哈佛大学
我们不用二氧化碳的碳酸 Instead of carbonic acid from carbon dioxide,
用更强的酸来取代 we're gonna use a little stronger acid
这样反应更快一些 to make it go a little faster.
这是硝酸 This is nitric acid
当我们加到石灰岩上的时候 and when we add it to the limestone,
它会溶解石灰岩 it will dissolve away the limestone
最终会形成非常清澈的溶液 and ultimately create a very clear solution,
你可以看到它在冒泡溶解 so you can see it bubbling away.
当我们把溶液倒入海洋里时 And when this is added to the ocean,
它们就发生反应并产生盖帽碳酸盐岩 it reacts and creates the cap carbonates
并覆盖在冰积层顶部 that blanket at the top of the glacial deposits.
但到现在也不是所有人都相信 But still not everybody is convinced that
地球曾被完全冰封 the planet was ever entirely covered in ice.
有科学家反驳 Some scientists argue that
生命体在雪地球里存活的几率几乎为零 the chances of life surviving a full-on snowball are virtually nil.
冰层之上 Above the ice,
严寒条件实在太严峻 the freezing conditions were too hostile;
冰层之下 生命体又接触不到阳光 while below it, life was cut off from sunlight.
然而确实有证据表明有能光合作用的微生物 Yet there is evidence that photosynthesizing organisms
确在冰层下存活 did survive the freeze:
单细胞的蓝藻细菌就在此期间存活了下来 single-celled cyanobacteria existed right the way through.
蓝藻细菌可以在极端气温下存活 Cyanobacteria can survive extremes of temperatures
不论是零上数十度或零下数十度 many degrees above and below zero.
但如果海洋一旦结冰 But if the oceans froze over,
极厚的冰层会将它们和阳关隔离开来 a thick layer of ice would have sealed them away from the sunlight.
当它们能量的来源被阻隔 With their energy source blocked,
它们就会灭绝 they would have died out.
如果你在雪地球期来临前潜水到热带珊瑚礁上 If you'd been diving on a tropical reef before snowball,
詹姆斯·格玲 南澳博物馆
这就是你会看到的东西 this is what you would've seen,
一片烂泥 海底有一丘一丘的烂泥 slime world. Mounds of slime on the seafloor.
如果你碰到它们 And if you touched them,
你会发现它们其实是岩石 you'd find out that they're actually rock.
但表面上都覆盖着黏呼呼的东西 A surface covered with slimy material,
那就是蓝藻细菌 which is actually cyanobacteria,
生命最原始的基本形态 the earliest, the most primitive form of life,
迄今为止已经有30亿年的历史了 that's been around for 3 billion years up until this point,
而且仍然存在至今 and is still around today.
反对者认为没有生命可以从全球大冻结 Critics argue that nothing could have survived
那样严酷的环境中存活下来 the ferocious conditions of a total global freeze.
他们坚持认为雪地球就是一段严重的冰期 They maintain snowball earth was nothing more than a severe ice age
即冰川延伸极广 只有赤道附近有一圈活水 with extensive glaciers and a belt of open water around the equator.
伦敦大学帝国理工学院的地质学家菲利普·艾伦 Phillip Allan, a geologist at Imperial College London,
认为冰冻星球理论的证据是不充分的 believes that the evidence for a frozen planet is flawed.
我并不认同雪地球的假说 I am not in agreement with the snowball earth hypothesis.
菲利普·艾伦 伦敦大学帝国理工学院
在我看来 这个观点最大的漏洞 The major hole in the theory as far as I am concerned
就是冰河时期的沉积岩堆叠 并不能支持 is the sedimentary rocks deposited during the glacial period do not support
长期的地球冰冻说 the idea of a long term global freeze.
菲利普·艾伦的反面论据 Phillip Allan's counter evidence
即形成于六亿五千万年前的石头上的类波纹图案 includes the ripple-like patterns in rocks formed 650 million years ago.
仔细观察这些沉积岩就能发现 When you look at these sedimentary rocks
这表明了无冰水域 it indicates open water.
风在水面拂过 由此形成了波纹 The wind was able to blow over the water surface and form ripples,
即海底形成的波纹 wave ripples on the seabed.
所以这也证实了当时是开放水面 So they are really conclusive proof of an open water surface
并没有被冰封闭起来 rather than an ice covered one.
开放水面的海浪在海底沉积岩上留下痕迹 Waves in an open sea left imprints in the sediment of the seafloor.
而当水不复存在 沉积物慢慢转变成石头 When the water disappeared and the sediment turned into rock,
波纹也保留了下来 the ripples remained.
艾伦等人提出了雪地球外的另一种假说 Allan and others propose an alternative to the snowball earth.
即融雪地球假说 It's known as the slushball.
在他们的假设中 In their version of events,
地球一直没有被完全冰冻 the earth never froze completely.
仍有部分地面和海洋未被冰封 Some patches of open land and sea remained.
可是冰球假设支持者并没有否认 But proponents of the snowball theory don't suggest
整个冰冻地球仍有露出来的部分 that the frozen planet was without any open water.
施拉格认为靠近地热能的冰洞处 Schrag believes that life could have survived in ice holes
生命可以存活 around sources of geothermal energy.
即便地球完全被冰雪覆盖 Even in a completely ice covered planet
仍有许多地方 there's still plenty of places
存在温泉还有火山产生的地热能 where there are hot springs, geo-thermal heat from volcanoes;
可能有成千上万的小冰洞 probably thousands and thousands of such little hole's
很多小冰洞 and in many of those little hole's
可以让生命度过了整个冰河时期 you could sustain life throughout the snowball earth period.
实际上我们可能永远不会知道 The reality is we may never know
地球是不是真的曾完全冻结过 if the world was ever completely frozen over.
有时人们会认为雪地球就像动画片 Sometimes people think of the snowball earth like a cartoon,
一颗很简单的星球 an over-simplified planet
但实际上情况却要复杂的得多 but the real world is much more complicated than that.
融雪地球也好 雪地球也罢 Whether slushball or snowball,
大家都认为地球曾出现过严重的冰冻 everyone agrees there was a profound global freeze.
而当六亿三千五百年前 地面渐渐显露时 And when our world emerged, 635 million years ago,
意想不到的事物出现了 something unexpected appeared.
生命 Life,
远比以往任何事物都要复杂 far more complex than anything that had gone before.
大冻结之后 地球上的生命迅速增长 After the big freeze, life on earth exploded.
Naked Science Snowball Earth
六亿五千年前 我们的星球 Our planet, 650 million years ago,
气温骤然下降 temperatures plummeted,
使得整个地球环境异常残酷 turning our planet into a hostile place.
神奇的是 生命存活了下来 Yet somehow, life survived.
随着冰雪逐渐融化 And as soon as the frozen earth began to thaw,
生命蓬勃发展 it blossomed,
物种史无前例地以爆发式速度增长 and there was an unprecedented explosion of life on earth.
在大冰冻之前 地球上只有原始的生命 Before the deep freeze, life was primitive.
单细胞原始微生物及蓝藻大都只存于海洋 Single-celled organisms and algae were mostly confined to the oceans.
而在大冰冻结束后不久 Shortly after it ended,
多细胞生物出现了 the first multicellular animals appeared.
有一个问题就是 The big question is,
是不是全球变冷导致了这次大规模进化 did the global cooling trigger this great leap in evolution?
最好的证据就是时间的重合 The best evidence is the coincidence in timing,
保罗·霍夫曼 哈佛大学
实际上第一块多细胞生物的化石 the fact that the first fossils of multicellular animals
在最后一次雪地球结束后不到三百万年形成 occur less than 3 million years after the last snowball termination.
肖书海是弗吉尼亚理工学院的地质学家 Shuhai Xiao is a geologist at Virginia Tech.
他发掘了一些最古老的多细胞生物的化石 He unearthed some of the oldest multicellular animal fossils in the world,
地点是中国南部的矿井底 in a mine in southern China.
化石非常小 The fossils are really small.
肖书海教授 弗吉尼亚理工学院
直径只有0.5毫米 They're about half millimetre in diameter.
所以裸眼几乎是看不到的 So you can barely see them with naked eyes.
在显微镜下 Under a microscope,
他发现这些化石是最原始动物的胚胎 he discovers that the fossils are very primitive animal embryos.
有些化石有二 四 八个甚至更多个细胞 Some fossils show clusters of 2, 4, 8 and more cells.
刚发现这些时我们真的很兴奋 It was really exciting when we found those.
这些是最早的生物体化石 Those are some of the earliest animal fossils
它们周围的岩石差不多 and they have found in rocks that were deposited
形成于雪地球刚结束的时期 almost immediately after the snowball earth ended.
这些动物胚胎的化石要追溯到 Fossils of these animal embryos date back to
三百万年前全球结冰刚好结束的时候 just 3 million years after the global freeze ended.
那对于人类来说是相当长的一段时间 That might seem a long time in human terms,
但地质学上 那只是一眨眼的功夫 but geologically, it's the blink of an eye.
而在接下来的八千万年中 Over the next 80 million years,
生物物种呈爆炸式增长 animal life exploded.
在澳大利亚南部的弗林德斯山脉 In the Flinders Ranges in southern Australia,
地质学家找到了一些复杂的多细胞生物的 geologists have found some of the oldest fossil evidence
最古老的化石 of complex, multicellular life.
这些生物与当今的物种几乎没有共同点 These creatures bear little resemblance to life today,
但为我们探寻早期生命的起源提供了线索 but they offer clues to the genesis of early life.
六亿五千年前 650 million years ago,
这一代还是一片浅海 this area was beneath a shallow sea.
奇怪的软体 譬如 Bizarre, soft-bodied organisms similar to
水母及扁形虫就生活在海底 jellyfish or flatworms lived on the seafloor.
一些生物陷在潮汐带来的 Some of the organisms got trapped in
细沙之中 并就此形成了化石 fine silt of tidal flows where they fossilized.
詹姆斯·格玲一直在研究这些早期生命 Jim Gehling has been investigating these early animals.
说不定我们的祖先就在这岩石之中 Probably our ancestors lie in these rocks.
这个生物叫狄更逊水母 This thing here, Dickensonia,
类似于薄烤饼或坐垫 是蠕虫类生物 can best be described as some kind of a pancake or mat-like worm creature.
它没有真正的头部 有内脏 It doesn't have a proper head, has what appears to be a gut,
身体有很多段 very fine segments.
但这也没解释地球的冰冻 But this doesn't explain how the severe planetary freeze
是如何催生出进化进程的大跃进的 could have triggered a leap in evolution.
我们知道的是 氧气的上升与 What we do know is that there is a striking coincidence
冰球时期的结束时间上惊人地巧合 between the rise of oxygen and the end of the snowball.
含氧量在地球冰期结束后上升 Oxygen levels rise following these global ice ages
因为冰和阳光能产生化学反应 because of a chemical reaction between ice and sunlight.
六亿五千年前 650 million years ago,
地球是没有臭氧保护层来阻止紫外线 there was no ozone to stop the sun's ultraviolet light
辐射地球上的冰面的 hitting the earth's icy surface.
紫外线与水蒸气反应产生了过氧化氢 This UV light reacted with water vapour to form hydrogen peroxide.
过氧化氢在冰中留存了几百万年 The hydrogen peroxide remained in the ice for millions of years.
当冰融化时 But when the ice melted,
氢都已经跑掉了 the hydrogen escaped,
而过氧化氢就转变成了水和氧气 and the peroxide converted into water and oxygen.
氧气就慢慢达到了现在的水平 Oxygen reached the same level as we have today.
大约在同一时间 At roughly the same time,
第一个复杂生命体就诞生了 the first complex animals appeared.
氧气增多促使多细胞生物的发展 More oxygen enabled life to become multicellular.
单细胞生物能从水中吸收氧气 A single cell can take up gases and oxygen from water.
氧气能通过细胞膜进入细胞内 Oxygen fuses across the cell membrane into the cell.
可当几个细胞连接在一起时 However, when several cells link together,
氧气很难在细胞间传递 it's harder for oxygen to diffuse from one cell to the next.
氧气的压力要更大 The pressure of oxygen needs to be higher.
你要有足够压力的氧气 You need to have a high enough pressure of oxygen
才能维持循环系统 to have a circulatory system
让氧气进入每一个细胞 bring the oxygen all around the body.
最后一次雪地球结束后 After the last snowball earth,
氧气含量终于足够 oxygen seems finally to have been high enough to support
维持海底成千上万早期小型生物的生存 hundreds, thousands, millions of small early animals on the seafloor.
氧气被证明是进化最好的催化剂 Oxygen turned out to be the lynchpin of evolution.
能够使用氧气 The ability to use oxygen
使得生命变得更加多样化 enabled life to become dramatically more diverse.
氧气比起我们能吸入的其他气体 Oxygen gives us 20 times more energy
约瑟夫·克茨芬克教授 加州理工学院
可以提供二十倍 or more than 20 times more energy
甚至是超过二十倍的能量 than any other thing that we can breathe or that life can breathe.
可以进化出更大型的动物 You can have bigger animals.
还能有更有活力的生物体 You can have more active organisms.
植物能将根部的水等养分传输到叶子上 You can have plants that grow and transport liquids from roots to the leaves.
还能让鸟可以飞起来 And, you know, you can have birds energetic enough to fly.
没有氧气 我们什么都不是 Without oxygen, we would all be slime.
冰冻地球也许能推动早期生命向前发展 A frozen earth may have given early life a push forward,
但地球如果再次冻结 人类将很难生存 but if the world were to freeze over again, we'd struggle to survive.
这种情况以前发生过好几次 We know it's happened several times before.
问题是 还会再发生吗 The question is: could it happen again?
我们有一个有利因素 太阳 One factor in our favour is the sun.
过去的48亿年之中 Over the last 4.8 billion years,
太阳变得越来越活跃 it has been getting more and more active
因为核聚变产生了大量的热量 as nuclear fusion generates more and more heat.
当今的太阳比起六亿五千年前温度提高6% The sun today is about 6% warmer than 650 million years ago.
所以在短期内 不大坑内会发生大冰冻 So in the short term, another deep freeze is unlikely.
当今的太阳更温暖 这可能对我们有利 The sun is warmer today; that probably helps us out
可只有科学家真正了解雪地球的诱因时 but until scientists really understand the cause of snowball earths,
我们才能确定类似的危险还会不会再发生 I don't think any of us know whether we're in danger or not of a recurrence.
然而还有一种因素会导致全球冰冻 But there is one possibility that could result in another global freeze:
那就是各大洲的位置改变 a shift in the position of the continents.
因为他们的地理位置会影响气候 We know their arrangement influences the climate.
如果大洲都向赤道靠拢的话 If the majority of the continents were clustered on or near the equator,
地球将更容易变成雪地球 the earth would be more likely to turn into a snowball.
温度降低会导致两极的海面不断结冰 Cooling temperatures would cause ice to form in the open ocean of the poles,
而与此同时各大洲还进行风化作用 while weathering would continue on the continents.
随着更多的碳锁在岩石中 气温便急速下降 With more and more carbon locked away, temperatures would plummet.
如果各大洲都在赤道附近 If all the continents were near the equator,
那地球将会越来越冷 then the earth could get colder and colder
海上的冰也会形成 and sea ice could form
并向低纬度延伸 不断向赤道靠拢 and get to lower and lower latitudes closer and closer to the equator.
现在我们的世界看似安全 Today our world seems safe.
各大洲也都更靠近两极 Most of the continents are near the poles.
但是地壳板块运动从没停止过 But plate movement never stops.
从这个角度看 几百万年后 At some point, millions of years in the future,
各大洲又会在赤道处集合 the continents may group around the equator once again.
我觉得是有这么一天的 I think it's possible some day,
如果大洲的位置发生很大的改变 if the continents were in a very different position,
那么几千万年之后 maybe hundreds of millions years from now,
我们将会再次遭遇雪地球 that we could indeed have another snowball earth.
也许人类没有机会目睹 It's unlikely that mankind will be around to
下一次雪地球 witness another snowball earth.
但地球依然存在 But the earth will still be here.
也正如同历史一样 And just like it has in the past,
地球会存活下来 our planet will survive
进入下一段奇妙的旅程 and enter a new phase in its extraordinary history.