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恐龙曾漫步南极洲 那时没有冰川有森林

更新时间:2019/3/17 9:34:56 来源:纽约时报中文网 作者:佚名

When dinosaurs roamed Antarctica
恐龙曾漫步南极洲 那时没有冰川有森林

Antarctica - icy, empty, desolate, cold - these are words you may use to describe it, but it hasn’t always been that way.

“冰冷,空虚,荒凉,寒冷”— 提到南极洲,这些词语便会不由自主地进入你的脑海里,但南极洲并非一直都那么寒冷。

There was once a time when the great southern landmass was covered in forests and dinosaurs roamed free. How could such an icy wilderness once have been so warm that it could support Earth’s most gigantic creatures?

曾经有一度时间,南极洲的大陆竟然是被森林覆盖着,恐龙能在森林里自由自在地漫步。南极洲这样一个冰冷的荒野怎么会有一段如此暖和的时期,甚至于地球上最巨大的生物都能够在此生存呢?

To understand this we have to go back in geological time. Antarctica was ice free during the Cretaceous Period, lasting from 145 to 66 million years ago. That long ago may seem unfamiliar but we know it because it was the last age of the dinosaurs before an asteroid hit the earth and ended their time on this planet.

要回答这个问题,我们必须追溯到远古的地质年代(Geological Time,指地质学或考古学用来划分地球历史的时间单位)。南极洲在白垩纪时期(Cretaceous Period,地质时代中的中生代最后一个纪,开始于1.45亿年前,结束于6600万年前)是无冰的。我们可能并不了解这个离我们如此久远的时期,但我们熟知白垩纪是因为它是小行星撞击地球并结束恐龙在地球上存活的最后一个时代。

During this time period there were forests at both poles. Fossils of trees and cold-blooded reptiles have allowed scientists to build up a picture of what the climate was like. Cold-blooded reptiles need the warmth of the sun to survive; today we see them basking in the sun to warm up during the day. At the poles where the sun disappears during the winter months it must have been warm enough for them to survive through the darkness.

在白垩纪时期,地球南北两极都有森林。是极地树木和冷血爬行动物的化石使科学家们获知南北两极曾有过暖和的气候。冷血爬行动物需要太阳的温暖才能生存,如今我们经常能看到它们白天在阳光下晒太阳。只有这样,在极地的冬季太阳消失时,它们才能够用保存的热度于阴冷的黑暗中活下来。

Scientists also use the shells of fossil organisms that lived in the ocean called foraminifera to understand past climate. By analysing the chemistry of their shells and knowing the age intervals when different species lived they can get an estimate of ocean water temperature during that time.

科学家们还使用生活在极地海洋中称为有孔虫(Foraminifera)的一种有机生物的化石壳来了解过去的气候。通过分析有孔虫化石壳的化学物质并了解不同物种生活时的年龄间隔,他们可以估算出那段时间的海水温度。

Dr Brian Huber from the Smithsonian Museum of Natural History investigates the Cretaceous with a particular focus on deep-sea sites around Antarctica. He explains; “foraminifera provide some of the best records because you've got both bottom dwelling ones living in the sediments and recording bottom ocean temperatures and then you've got the planktonic ones that live in the top fifty meters of the ocean recording atmospheric temperatures. When you couple those records through time and analyse the shells from different parts of the ocean all over the world, you get a really good idea of the evolution of climate.”

史密森尼自然历史博物馆(Smithsonian Museum of Natural History)的胡贝尔(Brian Huber)博士调查白垩纪时期时,特别关注南极洲周围的深海遗址。他解释说:“有孔虫提供了一些很有价值的记录,因为通过它们你可以得到居住在沉积物中的底栖生物以及海底温度的变化记录,然后你还会得到生活在海洋顶部五十米的浮游生物,后者记录着当时的大气温度。当你把这些记录与时间结合起来并分析来自世界各地海洋不同部分的贝壳时,你就会对气候的演变有一个很好的了解。”

Huber elaborates that what they found in the Southern Ocean around Antarctica was hard to believe at first because it just seemed too warm; “we found temperatures of 30C at 58 degrees south,” close to the Antarctic Circle.

胡贝尔详细解释说,科学家在南极洲周围的南极洋的发现起初是很难令人置信的,因为白垩纪似乎太暖和了,靠近南极圈的南纬58度海洋温度有30摄氏度。

These high temperatures occurred during the middle of the Cretaceous known as the ‘Cretaceous Hothouse’ - a hot greenhouse effect caused by increased carbon dioxide in the atmosphere. But what happened in the Cretaceous to create a world where there were trees and dinosaurs roaming Antarctica unlike the barren ice fields of today?

这些高温时期发生在白垩纪中期,被称为“白垩纪温室”。这是指由大气中二氧化碳增加引起的温室效应。但是在白垩纪究竟发生了什么事情,才会形成一个有树木和恐龙漫步的南极洲世界,而不是今天的贫瘠冰原?

Huber explains; “what we know about the mid-Cretaceous in particular is that we had much faster rates of sea floor spreading and so more volcanic sources of CO2.” Huber and colleagues are still investigating whether the ‘hothouse’ occurred as a result of a major amount of volcanism erupting CO2 and creating a greenhouse blanket that warmed the earth.

胡贝尔解释说:“白垩纪中期有一个明显特点那就是海床延展速度很快,因此火山频发,产生很高的二氧化碳。”胡贝尔及其同事仍在研究调查白垩纪温室是否因大量火山爆发频繁造成。火山爆发,释放出大量二氧化碳,在地球表面形成一个温室罩,使得地球的气温上升变暖。

We all know the climate changes, it has in the past, it is changing now and it will in the future, but what is different about what we are doing now compared to what happened in the Cretaceous? Could Antarctica be ice-free again soon?

我们都知道地球气候一直在变化,在过去,现在甚至未来,无时无刻都在发生着变化,但与白垩纪发生的情况相比,我们现在所经历的气候变化会有什么不同?南极洲有否可能再次进入无冰时期?

“It's really an unprecedented rate and magnitude of change compared to geologic events that we know of from the past. We're releasing hundreds of billions of tons of CO2 into the atmosphere in just a matter of decades. Volcanoes can't produce that amount of CO2 in such a short time span even if they are huge volcanoes;” says Huber.

胡贝尔说,“与我们所知的远古地质事件相比,当代气候的变化无论速度和幅度都是前所未有的。我们只几十年内时间就向大气释放了数千亿吨的二氧化碳。即使是巨大的火山也不能在如此短的时间内释放这么多的二氧化碳到大气中。”

In terms of the future, Huber suggests; “I think what we'll see possibly in decades, maybe centuries is what are called ice streams that start flowing faster and it could be that West Antarctica in particular starts to deglaciate. Given the rate at which ice flows, we won't see [the whole of] Antarctica deglaciate in a matter of decades. Glaciologists predict that once you start raising sea level you start getting a positive feedback where that allows ice to flow faster and sea level rises faster, so then it just sort of keeps going. So yes I think the signs are there already.”

就未来而言,胡贝尔建议道:“我想未来几十年,也许是几百年我们可能会看到我们所称的冰流将开始快速流动,特别是南极洲西部可能会开始脱冰。考虑到冰流的速度,我们不会在几十年内看到全部南极洲的冰川消融。但冰川学家预测,一旦海平面开始提高,就会出现碳循环反馈,使得冰流加速,海平面的上升也会加快,所以这个过程只会不断前进,不会停止或后退。所以我认为预示南极将无冰的迹象已经存在。”

We may not have dinosaurs roaming Antarctica again, but we can’t rule out it being ice free in the future, and we have no way of knowing what that would be like for humans as we have never lived on Earth when there wasn’t ice at the poles.

我们不会看到恐龙再次在南极洲漫步,但是我们不能排除将来南极洲会进入无冰时期的可能性,并且我们无法知道人类的生存状况在那时会是怎样的,毕竟地球上南北两极无冰的时候,人类还没有出现。

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