評論
打印
Science and technology
科學技術
Forensic zoology
法醫動物學
The elephant in the room
房間里的大象—保護大象，刻不容緩！
Dating ivory has just become easier. Poachers beware
確定象牙年代已變得更容易了，偷獵者們要小心嘍！
FEW megafauna are more charismatic than elephants, and that charisma gives them political clout.
在大型動物里，沒有幾種動物可以匹敵大象的魅力，這種魅力讓大象很有政治影響。
On July 1st, for example, Barack Obama used the Tanzanian leg of his tour of Africa to announce an executive order intended to give teeth to America's obligation, as a party to the Convention on International Trade in Endangered Species, to prevent the smuggling of poached ivory.
比如說今年7月1日，奧巴馬總統在非洲行程中的坦桑尼亞站宣布了一項行政命令，該命令旨在通過強制實施有效手段來更好地履行美國《瀕危野生動植物種國際貿易公約》的一員防止偷運偷獵象牙的義務。
The rules on trading ivory, though, are hard to enforce, for if it comes from an animal killed before 1990 such trade is legal.
但是，針對象牙貿易的規定很難實行，因為如果象牙來自的大象是在1990年之前被殺的，那么這種貿易是合法的。
Not surprisingly, a cottage industry in making ivory look older than it is has grown up.
因此，讓象牙看起來比實際年代更久的家庭手工業的發展壯大就并不奇怪了。
But a paper published in the Proceedings of the National Academy of Sciences, by Kevin Uno of the University of Utah and his colleagues, may deal with that.
猶他大學的Kevin Uno和他的同事發表在《美國國家科學院院刊》上的一篇論文可以解決這個問題。
For Dr Uno has worked out how to use one of science's less glorious episodes, the atmospheric testing of nuclear weapons, to work out exactly how old a piece of ivory really is.
因為Uno博士研究出了如何利用科學不甚光彩的一段—核武器大氣層實驗，來算出一節象牙的真實年代是多少。
Dr Uno's method uses the ivory's carbon-14 content in a way that was not previously employed.
博士Uno的方法用到了象牙的碳-14含量，他利用碳-14含量的方式從來沒人用過。
What radiochemists call 14C forms naturally in the atmosphere by the action of cosmic rays on nitrogen atoms.
被放射化學家稱作碳-14的物質是宇宙射線撞擊空氣中的氮原子而在大氣中自然形成的，
It has a half-life of 5,730 years, which makes it ideal for dating objects pertinent to human history, and it can do so to within a few decades of their true age—which is great for archaeology.
其半衰期約為5,730年，這讓其十分適合測量與人類歷史有關事物的年代，其測量誤差不超過其真實年代前后幾十年。
It is not, though, much use for finding out whether a particular piece of ivory was detached from the elephant that grew it before or after a specific date just over 20 years ago.
但碳定年法在測量象牙年代，看其生長的時期是在20年前的之前還是之后，則并無甚用武之地。
But Dr Uno realised there has recently been a second source of 14C—those bomb tests. And they give him the precision he requires.
但是Uno博士意識到最近碳-14還有另一個來源—那些核爆試驗，而這些試驗給了他他所想要的精度。
Normally, the amount of 14C in the atmosphere is governed by the rate at which cosmic radiation creates it and the rate at which things like photosynthesis absorb it.
通常來說，大氣中碳-14的數量取決于宇宙射線產生碳-14的速率和像光合作用一類的反應吸收碳-14的速率。
Between 1952 and 1962, however, when bomb tests above ground were commonplace, the amount of 14C in the air shot up until it was nearly double the normal level.
但是，在1952至1962年間，地面上的核爆試驗十分普遍，因此空氣中的碳-14數量驟升，達到了近正常值的兩倍。
Since then it has fallen, also quite steeply, as plants have absorbed the surplus.
但自那以后，碳-14的數量也急劇下降，因為植物把剩余的碳-14吸收掉了。
And it will continue to fall until the old equilibrium reasserts itself.
并且碳-14的值會不斷下降，直到降到原來的平衡值。
This bomb curve, as it is known, changes so fast that year-by-year differences in the 14C levels of recent specimens should be detectable.
我們知道，這種爆炸曲線的變化如此之快，因此我們就可以探測出近期空氣中每年碳-14值的不同。
To test this hypothesis, Dr Uno and his colleagues looked at 29 specimens of known age, from 1905 to 2008.
為對這一假想進行測試，Uno博士和他的同事研究了已知年代，即從1905年至2008年的29個樣品。
These included elephants' tusks, teeth and tail hair, and hippopotamus teeth.
這其中包括大象的長牙、牙齒和尾部的毛發，還有河馬的牙齒。
They measured the specimens' 14C content using a sensitive technique called accelerator mass spectrometry.
他們使用一項被稱作加速器質譜的高靈敏度技術來測量樣品中碳-14的含量。
For those tissues that had grown after 1955 the 14C concentration did, as the researchers hoped it would, closely match the bomb curve.
正如研究者們所預料的那樣，對于1955年以后生長的組織，其碳-14濃度與爆炸曲線嚴格吻合。
Indeed, for these the match was so good that their ages could be determined to within a year of the truth.
的確，對于這些樣品來說，吻合度如此之高，以至于對其年代的確定可精確到一年以內。
At the moment Dr Uno's technique costs 1,000 a pop, so some places, particularly poorer countries in Africa, might be reluctant to deploy it.
由于Uno博士的技術每次要耗費一千美元，因此有些地方，尤其是非洲更貧困的地區就可能不愿使用這種技術了。
But in the context of an illegal trade in ivory reckoned to be worth about 1 billion a year, that is not a huge amount of money.
但是，鑒于非法象牙貿易一年約價值十億美元，這就不是一個大的數目了。
And if it helps preserve elephants, whose numbers in Africa have fallen from 1.3m to 600,000 in the past 40 years, many would see it as money well spent.
而且，如果這種技術有助于保護大象，那么很多人會認為這個錢花得很值，因為在過去的40年里，大象的數量已從一百三十萬下降到了六十萬。
