Rather than restate every one, scientists decided to keep the inaccurate constant. "Thus," Tim Flannery notes, "every raw radiocarbon date you read today is given as too young by around 3 percent." The problems didn't quite stop there. It was also quickly discovered that carbon-14 samples can be easily contaminated with carbon from other sources—a tiny scrap of vegetable matter, for instance, that has been collected with the sample and not noticed.
科學家們沒有修正每個計算結果，而是決定保留這個不準確的常數。“這樣，”提姆·弗蘭納里說，“你只要把今天見到的每一個以放射性碳年代測定法測定的年代減去大約3%。”問題沒有完全解決。人們又很快發現，碳－14的樣品很容易被別處的碳污染──比如，一小點兒連同樣品一起被采集來的而又沒有被注意到的植物。
For younger samples— those under twenty thousand years or so—slight contamination does not always matter so much, but for older samples it can be a serious problem because so few remaining atoms are being counted. In the first instance, to borrow from Flannery, it is like miscounting by a dollar when counting to a thousand; in the second it is more like miscounting by a dollar when you have only two dollars to count.
對于年代不大久遠的樣品來說──年代小于大約2萬年的樣品──稍有污染并不總是關系很大，而對于年代比較久遠的樣品來說，這有可能是個嚴重的問題，因為統計中的剩余原子數實在太少了。借用弗蘭綱納里的話來說，在第一種情況下，就像是1000美元里少數1美元；而在第二種情況下，就像是僅有的2美元里少數了1美元。
Libby's method was also based on the assumption that the amount of carbon-14 in the atmosphere, and the rate at which it has been absorbed by living things, has been consistent throughout history. In fact it hasn't been. We now know that the volume of atmospheric carbon-14 varies depending on how well or not Earth's magnetism is deflecting cosmic rays, and that that can vary significantly over time. This means that some carbon-14 dates are more dubious than others. This is particularly so with dates just around the time that people first came to the Americas, which is one of the reasons the matter is so perennially in dispute.
而且，利比的方法是以如下假設為基礎的，即大氣里碳－14的含量以及生物吸收這種物質的速度，在整個歷史進程中是始終不變的。事實并非如此。我們現在知道，大氣里碳－14的數量變化不定，取決于地球的磁場能否有效地改變宇宙射線的方向；在漫長的時間里，變化的幅度可能很大。這意味著，有些以碳－14年代測定法測定的年代要比別的這類年代更無把握。在比較缺少把握的年代當中，有人類首次抵達美洲前后這一段時期的年代。這就是為什么那個問題老是爭論不休的原因之一。
來源:可可英語 http://www.ccdyzl.cn/Article/201703/495836.shtml
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