前苏联气象分析员Mikhail Budyko Soviet climate modeller Mikhail Budyko
演示了runaway ice-albedo是怎么 demonstrated how runaway ice-albedo
让降温冷却的地球完全冻结的 could cause a cooling earth to freeze completely.
正如他许多同时代的人一样 Like many of his contemporaries,
Budyko也很担忧核冬天的影响 Budyko was worried about the affects of a nuclear winter.
核冬天是指核爆炸产生的烟尘云团 Nuclear explosions create clouds of smoke and dust,
会阻碍太阳的能量 which block the sun's energy
并降低地球的温度 and lower the earth's temperature.
Budyko开发了一个数学建模 Budyko developed a mathematical model
来计算出全球进入冰期的几率 to work out the odds of a global ice age.
他的演示显示出如果地球的气候 He showed that if the earth's climate cooled enough
冷到了让低纬度结冰的话 for ice to form in the lower latitudes
那么ice albedo就会更快地上升 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,
整个地球就会变成一个大雪球状 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
而且一旦它极其迅速地接触到30度纬度时 and once they hit that latitude very, very rapidly,
整个地球都会埋在雪里 the earth would have been entombed in ice.
Budyko开拓性的研究表明了 Budyko's ground-breaking work
这个滚雪球效应是怎么 showed how this snowballing effect
在短短几十年里让 could create a totally frozen planet
整个地球变成冰冻星球的 within just a few decades.
Budyko的研究极其重要 Budyko's work was extremely important
它展示了地球是很有可能 in demonstrating that it was possible
陷入气候灾难的 that earth might slip into a climate catastrophe
完全冰封的灾难 which was covered completely with ice.
在他之前还没有人意识到这种可能性 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,
那么几乎它吸收的所有太阳的热量 nearly all the heat it received from the sun
都会被反射回太空 would be reflected back into space.
那么地球就被封锁在冰里了 The planet would become locked in ice.
所以如果说runaway freezing让地球封在冰里 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?
有科学家提出 在6亿5千万前年 Some scientists suggest that 650 million years ago,
我们的地球曾被完全冰封于冰河时代 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引发的结果" the result of a set of improbable triggers.
他们之前大约是这么想的 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.
这个证据就是南非的 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
您看到的这些是在赤道附近形成的 these formed near to the equator.
地理学家Paul Hoffman认为 Geologist Paul Hoffman believes
这可以证明 this is could be proof
地球这一辈子至少 that the earth froze over completely
完全冻结过两次 at least twice in its history.
最能证明22.2亿年前 The best evidence for a snowball earth
地球是个大雪球的 2.22 billion years ago
就是南非的古地磁证据 is paleomagnetic evidence from South Africa.
那里还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.
这样的发现更能说明 This discovery raised the possibility
雪地球理论并非单一事件 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 Scientists raced to find the trigger
早期深层冻结的诱因 for this earlier deep freeze.
冷却说似乎很符合 The cooling appeared to coincide
大氧化事件的表现 with the great oxidation event.
在海洋的深处 Deep in the ocean,
某些最古老的生命体最终 some of the oldest organisms on earth
进化出了光合作用的机能 evolved a mechanism called photosynthesis:
具有了利用太阳的能量 the ability to convert carbon dioxide
把二氧化碳转变为氧气的能力 into oxygen using the sun's energy.
当这些能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,
太阳还很弱 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.
但是光合作用消耗二氧化碳 But photosynthesis uses up carbon dioxide.
光合作用也产生氧气 It also produces oxygen,
这也破坏了沼气 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.
我们地球原是需要沼气的温室星球 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.
可能第一个光合作用的细菌 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
就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(沼气)量暴跌 methane levels tumbled.
失去了温室气体 With the loss of that greenhouse gas,
地球盘旋跌至深度冻结 the earth spiralled into a deep freeze.
这是一个蛮吓人的结果 It's kind of a frightening conclusion
一个单细胞的变异小虫 that a single celled mutant bug
毁掉了整个行星生态系统 destroyed an entire planetary ecosystem.
毁了 Destroyed it.
把地球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 And each time,
情况都不一样 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.
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
有红灰色的岩石层 sit layers of a peculiar reddish-grey rock.
这些岩石层在Flinders Range, Death Valley These layers stretch for miles
延展几公里 in the Flinders Range, Death Valley
在冰成岩出现的几乎所有地方都能看到它 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.
然而在这 But here,
它们却出现在冰积层的顶端 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.
这就是被冰划过的石头 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 and these are little grains
也是从冰山上掉落的 that also fell out of an iceberg,
直接落到这上面 and immediately on top of that
字幕 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 Their presence is evidence
温度猛烈骤增的证明 of a sudden and drastic temperature increase.
只有一样东西会引发这个情况 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
绝对要高于现如今的350倍 had to be around 350 times higher than they are today.
但如果整个地球都被极厚的冰层包围 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?
Caltech的教授Joe Kirschvink揭开了真相 Caltech professor Joe Kirschvink had a revelation.
我大半夜里醒来就说: 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
比如像黄石公园里的Aleutians like in the Aleutians, in Yellowstone...
这些火山还在 而且它们会向天空喷发二氧化碳 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 volcanoes would have continued
巨大量的二氧化碳 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 there would have been no mechanism
从大气中移除冰层 to remove it from the atmosphere.
所以经过了数百万年 Over millions of years,
温室气体的水平才慢慢提高 levels of this greenhouse gas would have built up,
最终产生了足够的热量 eventually producing enough warming
才脱离了ice albedo to off-set the ice albedo.
冰融化了 The ice melted,
导致全球气温旋转性上升 sending global temperatures spiralling upwards.
当融冰的水蒸发时 As this melted ice water evaporated,
大气层也因潮湿而肿胀 it swelled the atmosphere with moisture,
产生了猛烈的降水 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 Here, layers of carbonate sediment
累积在海底 accumulated on the seafloor
就形成了碳酸盐岩 to become carbonate rock.
Dan Schrag为我们演示整个过程 Dan Schrag demonstrates what could have happened.
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…………………………………… 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
地球曾经被冰雪封埋过 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 the chances of life surviving a full-on snowball
几乎为零 are virtually nil.
冰层之上 Above the ice,
严寒条件实在太苛刻 the freezing conditions were too hostile;
然而在冰层之下 while below it,
生命体接触不到阳光 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
能在冰封环境下存活: did survive the freeze:
单细胞的……………… single-celled cyanobacteria existed right the way through.
字幕 Cyanobacteria can survive extremes of temperatures
零上和零下的很多温度 many degrees above and below zero.
但如果海洋一旦冻上了 But if the oceans froze over,
极厚的冰层可能就把它们密封起来 a thick layer of ice would have sealed them away
完全接触不到阳光 from the sunlight.
当它们能量的来源被阻塞 With their energy source blocked,
它们就必死无疑 they would have died out.
字幕 If you'd been diving on a tropical reef before snowball,
字幕 this is what you would've seen,
字幕 slime world.
字幕 Mounds of slime on the seafloor.
字幕 And if you touched them,
字幕 you'd find out that they're actually rock.
字幕 A surface covered with slimy material,
字幕 which is actually cyanobacteria,
字幕 the earliest, the most primitive form of life,
字幕 that's been around for 3 billion years up until this point,
字幕 and is still around today.
字幕 Critics argue that nothing could have survived
字幕 the ferocious conditions of a total global freeze.
字幕 They maintain snowball earth was nothing
字幕 more than a severe ice age
字幕 with extensive glaciers
字幕 and a belt of open water around the equator.
Phillip Allan Phillip Allan, a geologist at imperial College London,
字幕 believes that the evidence for a frozen planet is flawed.
字幕 I am not in agreement with the snowball earth hypothesis.