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Since the first use of fingerprints to identify and convict a murderer, in 1892,
自從1892年首次使用指紋來識別并定罪謀殺犯以來，
detectives the world over have come to rely heavily on print evidence to build their cases against suspects.
世界各地的偵探都開始嚴重依賴指紋證據來建立針對嫌疑人的案件。
One limit on the value of fingerprints, though, is that it is hard to work out how old they are.
然而，指紋價值的一個限制是很難計算出它們的年代。
This is a particular problem when a crime is committed somewhere
當犯罪發生在犯罪嫌疑人經常且正當出入的場所，如工作地時，
that a suspect frequently and legitimately visits, such as a place of work.
這個問題就特別的突出。
In this case exactly when a print was made might be crucial to establishing guilt or innocence.
在這種情況下，準確的指紋時間可能是確定有罪或無罪的關鍵。
But it is information that science has, until now,been unable to provide with any accuracy.
但是直到現在，科學還不能提供任何準確的信息。
As they write in Analytical Chemistry, Paige Hinners and Young Jin Lee of Iowa State University
正如他們在《As they write in Analytical Chemistry》所寫的那樣，愛荷華州立大學的
believe they can remedy this state of affairs. They knew from work conducted by other laboratories
Paige Hinners和Young Jin Lee認為他們可以改變這種狀況。他們從其他實驗的工作中了解到
that the triglyceride oils contained in fingerprints change by oxidation over the course of time.
指紋中所含的甘油三脂油會隨著時間的推移而氧化。
That provides an obvious way to date prints.
這為推算指紋時間提供了一種明顯的方法。
The problem is that the techniques which have been applied to analyse these oils are able to distinguish age only crudely.
問題是用來分析這些油的技術只能粗略地分辨出年代。
In practice, they can determine whether or not a print is over a week old, but nothing else.
在實踐中，他們可以確定一個指紋是否已經超過一周了，但除此之外別無其他。
Dr Hinners and Dr Lee wondered if higher precision could be obtained by thinking a bit more about oxidation.
Hinners博士和Lee博士想知道更高的精確度是否可以通過更多地考慮氧化來獲得。
Oxygen molecules in the air come in two varieties. Most have a pair of atoms but some, known as ozone, have three.
空氣中的氧分子有兩種，大多數都有一對原子，但也有一些被稱為臭氧的有三個原子。
Though far rarer than diatomic oxygen, ozone is more reactive and also reacts in ways different from those of its two-atomed cousin.
盡管臭氧比雙原子氧更加稀有，但它的反應性更強，而且反應方式也與雙原子氧不同。
The two researchers therefore decided to focus their attentions on ozonolysis, as triatomic oxidation is known.
因此，這兩位研究人員決定將他們的研究重點放在臭氧（即三原子氧化）的分解上。
Triglycerides, as their name suggests, are three-tailed molecules.
甘油三脂，顧名思義，是三尾分子。
Each tail is a chain of carbon atoms, with hydrogen atoms bonded to the carbons.
每條尾巴都是一個碳原子鏈，氫原子連著碳原子。
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