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万物简史(MP3+中英字幕) 第218期:把铅撵出去(7)

时间:2017-03-06 16:33:00 来源:可可英语编辑:villa 可可英语APP下载 | 可可官方微信:ikekenet

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Rather than restate every one, scientists decided to keep the inaccurate constant.
科学家们没有修正每个计算结果，而是决定保留这个不准确的常数。

"Thus," Tim Flannery notes, "every raw radiocarbon date you read today is given as too young by around 3 percent."
“这样，”提姆·弗兰纳里说，“你只要把今天见到的每一个以放射性碳年代测定法测定的年代减去大约3%。”

The problems didn't quite stop there.
问题没有完全解决。

It was also quickly discovered that carbon-14 samples can be easily contaminated with carbon from other sources,
人们又很快发现，碳－14的样品很容易被别处的碳污染，

a tiny scrap of vegetable matter, for instance, that has been collected with the sample and not noticed.
比如，一小点儿连同样品一起被采集来的而又没有被注意到的植物。

For younger samples—those under twenty thousand years or so—slight contamination does not always matter so much,
对于年代不大久远的样品来说──年代小于大约2万年的样品──稍有污染并不总是关系很大，

but for older samples it can be a serious problem because so few remaining atoms are being counted.
而对于年代比较久远的样品来说，这有可能是个严重的问题，因为统计中的剩余原子数实在太少了。

In the first instance, to borrow from Flannery, it is like miscounting by a dollar when counting to a thousand;
借用弗兰纲纳里的话来说，在第一种情况下，就像是1000美元里少数1美元；

in the second it is more like miscounting by a dollar when you have only two dollars to count.
而在第二种情况下，就像是仅有的2美元里少数了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,
而且，利比的方法是以如下假设为基础的，即大气里碳－14的含量以及生物吸收这种物质的速度，

has been consistent throughout history.
在整个历史进程中是始终不变的。

In fact it hasn't been.
事实并非如此。

We now know that the volume of atmospheric carbon-14 varies depending on how well or not Earth's magnetism is deflecting cosmic rays,
我们现在知道，大气里碳－14的数量变化不定，取决于地球的磁场能否有效地改变宇宙射线的方向；

and that that can vary significantly over time.
在漫长的时间里，变化的幅度可能很大。

This means that some carbon-14 dates are more dubious than others.
这意味着，有些以碳－14年代测定法测定的年代要比别的这类年代更无把握。

This is particularly so with dates just around the time that people first came to the Americas,
在比较缺少把握的年代当中，有人类首次抵达美洲前后这一段时期的年代。

which is one of the reasons the matter is so perennially in dispute.
这就是为什么那个问题老是争论不休的原因之一。

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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.

科学家们没有修正每个计算结果，而是决定保留这个不准确的常数。“这样，”提姆·弗兰纳里说，“你只要把今天见到的每一个以放射性碳年代测定法测定的年代减去大约3%。”问题没有完全解决。人们又很快发现，碳－14的样品很容易被别处的碳污染──比如，一小点儿连同样品一起被采集来的而又没有被注意到的植物。

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.

对于年代不大久远的样品来说──年代小于大约2万年的样品──稍有污染并不总是关系很大，而对于年代比较久远的样品来说，这有可能是个严重的问题，因为统计中的剩余原子数实在太少了。借用弗兰纲纳里的话来说，在第一种情况下，就像是1000美元里少数1美元；而在第二种情况下，就像是仅有的2美元里少数了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设为基础的，即大气里碳－14的含量以及生物吸收这种物质的速度，在整个历史进程中是始终不变的。事实并非如此。我们现在知道，大气里碳－14的数量变化不定，取决于地球的磁场能否有效地改变宇宙射线的方向；在漫长的时间里，变化的幅度可能很大。这意味着，有些以碳－14年代测定法测定的年代要比别的这类年代更无把握。在比较缺少把握的年代当中，有人类首次抵达美洲前后这一段时期的年代。这就是为什么那个问题老是争论不休的原因之一。

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重点单词		查看全部解释
inaccurate	[in'ækjurit]	想一想再看 adj. 不准确的，错误的
absorbed	[əb'sɔ:bd]	想一想再看 adj. 一心一意的；被吸收的 v. 吸收；使全神贯注（
perennially	[pə'reniəli]	想一想再看 adv. 永久地
assumption	[ə'sʌmpʃən]	想一想再看 n. 假定，设想，担任(职责等), 假装	联想记忆 X 单词assumption 联想记忆： as加强动作+sumpt拿，取+ion→假设，承担
dispute	[di'spju:t]	想一想再看 v. 争论，争议，辩驳，质疑 n. 争论，争吵	联想记忆 X 单词dispute 联想记忆： dis反+pute认为，思考→过来思考→反驳
sample	['sæmpl]	想一想再看 n. 样品，样本 vt. 采样，取样	联想记忆 X 单词sample 联想记忆： s[=se分开]+ample拿，获得→分开拿出→样品，标本
consistent	[kən'sistənt]	想一想再看 adj. 始终如一的，一致的，坚持的	联想记忆 X 单词consistent 联想记忆： con共同，sist站－一堆士兵站成一排－前后一致的con共同，sistent＝sister：双胞胎姐妹的想法总是：前后一致的
restate	[ri:'steit]	想一想再看 vt. 重申	联想记忆 X 单词restate 联想记忆： re再，state（v 声明；陈述）
atmospheric	[.ætməs'ferik]	想一想再看 adj. 大气的，大气层的，制造气氛的
counted	[kaunt]	想一想再看 vt. 计算；认为 vi. 计数；有价值 n. 计数；计