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上周 当你听说巨大冰山从南极洲分离的时候
Climate change may have been on your mind last week
你可能会想到气候变化
when you heard about that gigantic iceberg breaking off Antarctica.
这块从南极洲分离出来的冰山是拉森C冰架的一部分
This piece of ice separated from a part of the continent called the Larsen C ice shelf.
它重约一万亿吨 大概跟特拉华州差不多大
It weighs some one trillion metric tons, it’s roughly the size of the state of Delaware,
面积将近5800平方千米 而它现在漂浮在南大洋
about 5800 square kilometers, and now it is floating in the Southern Ocean.
我们好像身处于环境灾难片中的情节里一样
And now we’re in the plot of an environmental disaster movie.
冰山断裂 融化 突然之间一片汪洋
Icebergs break off, they melt, and suddenly it’s Waterworld.
但是此处没有必要太惊慌
But there’s no need to panic here.
因为冰山是冰架的一部分 当它崩解的时候已经在漂浮了
Because the iceberg was part of an ice shelf, it was already floating when it broke off.
在冰漂浮时 它就已经占据了与其融化后等量的水
And when ice floats, it already displaces the same amount of water it’ll become when it melts.
所以这次事件不会加重海平面的上升
So this event won’t be adding to rising sea levels.
而且 研究人员也不对此感到惊讶
Also, it wasn’t a surprise to researchers
它事实上可能与气候变化也没有什么关系
and it might not actually have had much to do with climate change.
当然 人为影响的气候变化正在发生
Human-caused climate change is happening, of course,
而且已经对南极洲造成了影响
and it’s already made an impact on Antarctica.
但科学家们表示 据他们所知 这次并不是直接关联的事件
But scientists say that, from what they can tell, this isn’t a directly related event.
冰山从冰川分离出来是自然现象
Icebergs breaking off glaciers is a normal process.
这就是科学家们所说的裂冰作用
It’s something scientists call calving,
虽然与牛生牛宝宝不同
although different from when a cow has a baby cow.
冰川向水面延伸 形成漂浮的冰架
As glaciers extend out over water, they form floating ice shelves.
而且随着这些冰架继续移动
And as these shelves continue to move
边缘变得不稳定 当到达临界点
they reach a point where the edge of the ice can become unstable
就会分离出冰山
and they shed an iceberg.
在拉森C的案例中 科学家们已经从七年前就开始追踪冰架中的一条裂缝了
In the case of Larsen C, scientists have been following a crack in the shelf for 7 years,
所以我们已经预料到这些会发生了
so we’ve been expecting this to happen for while.
这成为头条 是因为这座冰山比通常要大得多
It’s mostly making headlines because this ‘berg is much bigger than usual
它占整个拉森C冰架的12％
12% of the entire Larsen C ice shelf!
还有些坏消息
There’s some bad news, too.
研究冰山和冰川的冰河学家 知道当冰山崩解时
Glaciologists, the scientists who study ice and glaciers, know that when icebergs calve,
更可能使岸冰崩塌
it can make the land ice more likely to collapse.
越来越多的冰会倾入大洋 因为能阻挡它们的冰架越来越少
More ice could dump into the ocean because less of the ice shelf is there to block it
这会引起海平面上升
which can raise sea levels.
拉森C冰架还有机会自我重塑 而不是完全崩塌
There’s still a chance that Larsen C could rebuild itself instead of totally breaking down
但是依据追踪记录来看 形势并不乐观
but the track record isn’t great.
比它小点的邻居 拉森B冰架在2002年部分崩解
Its smaller neighbor, the Larsen B ice shelf, partially collapsed in 2002,
那是崩裂出其自己的冰山的七年后
seven years after calving its own iceberg.
气候变化不是玩笑
Climate change is no joke
不过庆幸的是这座冰山并没有传达出世界末日的信号
but thankfully this one iceberg is not ushering in the end of the world.
与此同时 考古学家们这周表示
Meanwhile, archeologists this week reported
他们已经找到了人类在65000年前到达澳洲的证据
that they’d found evidence humans arrived in Australia 65,000 years ago
这比之前的预计要早大约5000年
which is about 5,000 years earlier than anyone expected.
来自昆士兰大学的一个团队在一个名为Madjedbebe的岩洞中
A team from Queensland University dug up around 11,000 new artifacts
发掘出了大约11000件史前器物
from a rock shelter called Madjedbebe
这个地方在二十世纪七八十年代进行过两次发掘
which had been excavated twice before in the 1970s and ’80s.
在早前的发掘中 考古学家们找到了一些石器
In those first digs, archeologists had found some stone tools
以及多块叫做赭石的天然颜料
and pieces of natural pigment called ochre
他们认为这些颜料有五万到六万年的历史了
that they thought were fifty to sixty thousand years old
这表明在那前后人类已经在澳洲出现了
which suggested that humans might have shown up in Australia around then.
但那时科学家还没有真正完善测定如此古老物体年代的技术
But this was before scientists had really perfected their dating techniques for things that old.
发射性碳测定年代法使用特定碳原子衰变的程度作为计时器
Radiocarbon dating, which uses the predictable, radioactive decay of certain carbon atoms as a clock
只能向前测定约五万年
can only really go back around 50,000 years.
其他能将把预测年代推得更远一点的方法才刚刚开始研究
Other methods that could go back much further were only just getting started.
所以那些技术可能产生多达20000年的估计误差
So those techniques might have skewed estimates by as much as 20,000 years,
但这也不会产生很大的影响
which is nothing to shake your spear at.
除此之外 许多考古学家认为
Besides all of that, many archeologists thought
当地的土石层被严重破坏
that the layers of dirt and rock at the site had been disrupted enough
以致于他们无论如何也不能真正相信预测的年代
that they couldn’t really trust the dates anyway.
所以在2012和2015年 研究人员带着更新的技术返回岩洞 来看看有什么发现
So, in 2012 and 2015, researchers went back to the site to see what they could turn up with newer methods
第三次的发掘令人振奋！
and the third time was the charm!
团队发现了成千上万的新物品：研磨石 赭石蜡笔
The team found thousands of new objects: grinding stones, ochre crayons
还有世界上最古老的短柄石斧
and the oldest edge-ground hatchets in the world.
为了测定这些新器物的年代 团队使用了名为“光释光”的技术（OSL）
To date the new artifacts, the team used a technique called optically stimulated luminescence, or OSL
这项技术可以揭露矿物最后一次接触阳光的时间
which reveals the last time a mineral was exposed to sunlight.
基本来说 科学家们往岩块的石英颗粒上照射光线
Basically, scientists can shine a light on quartz grains in rocks
来释放岩石数个世纪以来从环境中获得的辐射能量
to release radioactive energy they’ve picked up from the environment over centuries
然后通过测量这些能量判断石器的年代
and measuring that energy can tell how old the rock artifacts are.
通过OSL技术 这个团队可以确定更遥远的年代
With OSL, the team was able to confirm the earlier dates.
他们将最古老器物的年代回推到更远
And they pushed back the age of the oldest artifacts even further,
大约65000年前 只有几千年的误差
to around 65,000 years ago, with just a few thousand years of uncertainty.
这个发现帮助我们了解
This discovery helps us understand
在多早之前人类就开始适应其它原始人类和动物物种了
how early humans fit in with other hominid and animal species.
这么早的时代意味着人类在从东南亚到澳洲的过程中
The earlier time frame means humans making their way from Southeast Asia into Australia
可能与其它原始人类进行过较长时间的异种交配
maybe had longer to interbreed with other human-like hominins
如丹尼索瓦人 或者我们最近的亲戚之一——直立人
like the Denisovans or Homo erectus, one of our closest relatives.
这些早期人类可能与曾生活在澳洲的巨型动物生活过更长的时间
And these early humans likely spent more time with huge animals that used to live in Australia.
因为如果你认为现在澳洲拥有奇特生物
Because if you thought Australia had weird animals now,
它曾经还有巨大的 重达两吨的袋熊
it also used to have gigantic, two-ton wombats.
对于那些巨型生物 例如袋熊和短脸袋鼠
Scientists have debated for years whether giant creatures like those wombats and the short-faced kangaroo
是否由于人类或气候变迁或两者都有而灭绝 科学家们已争论多年
died out because of humans, climate change, or some mix of the two.
这些最新的发现并不足以完全解决这一问题
The latest finding doesn’t fully resolve that issue
但是它的确表明这些大型动物在灭绝之前曾与人类共同生活过约20000多年
But it does suggest that these big animals lived with humans for about 20,000 years before going extinct.
所以这并不像某些科学家们认为的那样是快速的屠杀（导致巨型生物的灭绝）
So it wasn’t as quick a kill as some scientists had proposed.
从南极洲的冰山到澳洲的早期人类
From the iceberg in Antarctica to early humans in Australia
对于地球的过去 现在以及未来 我们仍然有许多问题要弄清楚
there’s still a lot we’re figuring out about Earth’s past, present, and future
不过我们正在成功的路上
but we’re getting there!
说一下未来：一个月后美国大日蚀就要来临了
Speaking of the future: the Great American Solar Eclipse is just a month away!
如果你对此感兴趣的话
If you’re interested in learning more about it
你可以在Scishow太空频道youtube.com/scishowspace上查看
you can check out our episode on that at the SciShow Space channel at youtube.com/scishowspace.
如果你想找个安全的方法观看日蚀
And if you’re looking for a safe way to see the eclipse
我们为你准备了SciShow特制的针孔成像器
we’ve got you covered with our special SciShow pinhole projector card!
你要做的就是在中间刺一个小洞
All you have to do is poke a hole in the middle
拿一张纸用来投射图像
grab a piece of paper to project the image onto
然后调节卡片和纸张距离
and adjust the distance between the card and the paper
直到你能清楚地看到日蚀图像
until you see a clear image of the eclipse
这个小洞的作用与照相机的镜头相似
The tiny hole acts kind of like the lens in a camera
将穿过它的光聚焦 在其后的纸上成像
focusing the light that passes through it to make an image on the paper behind it.
你可以在dftba.com/scishow上获取这个针孔成像器
You can get your SciShow pinhole projector at dftba.com/scishow!
［结尾］
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