評論
打印
Listen to part of a lecture in a geology class.
聽一段地質學課程。
Ok, let's get started.
好吧，我們開始上課。
Great.Today I want to talk about a way in which we are able to determine how old a piece of land,
今天我要談一些關于如何測定地質年份和其他關于地質特征的方法——年代測量法。
or some other geologic feature is - dating techniques.
為什么我要講一些特殊的測定法呢？
I'm going to talk about a particular dating technique.Why?
為什么我要講一些特殊的測定法呢？
Good dating is a key to good analysis.
一個準確的年代是一把打開分析之門的鑰匙。
In other words, if you want to know how a land formation was formed, the first thing you probably want to know is how old it is.
換句話說，如果你想知道這塊地質形成的原因，你要做的第一件事就是搞清楚 它的“年紀”了。
It's fundamental.
這是基礎的東西。
Um take the Grand Canyon for instance.
嗯，舉個大峽谷的例子。
Now, we geologists thought we had a pretty good idea of how the Grand Canyon in the southwestern United States was formed.
現代地質學家認為我們已經形成了一個沒有太多瑕疵的關于美國西南部大峽谷起源的假說。
We knew that it was formed from sandstone that solidified somewhere between 150 and 300 million years ago.
我們推測它的形成源于 15 至 30 億年間砂巖的凝固。
Before it solidified, it was just regular sand.
在成型之前，這些只是普通的沙子。
Essentially it was part of a vast desert.
本質上是沙漠的一部分。
And until just recently, most of us thought the sand had come from an ancient mountain range fairly close by that flattened out over time.
直到最近，我們中的多數人才認識到這些沙子來自近旁的一處古老山脈，那山脈隨著時間的流逝曲線漸消，趨于平穩。
That's been the conventional wisdom among geologists for quite some time.
這是那段時間地質學家的傳統測量方法。
But now we 've learned something different, and quite surprising, using a technique called Uranium Lead Dating.
但是現在我們得到了不同的方法和更多的驚喜，這種我們至今仍在使用的技術被稱為“鈾鉛年份測試法”。
I should say that Uranium Lead Dating has been around for quite a while.
雖然說鈾鉛年份測試法問世已經有一段時間，
But there have been some recent refinements.
但它也經歷過幾次改良。
I will get into this in a minute.
等一下我們就會講到。
Anyway, Uranium Lead Dating has produced some surprises.
總之，鈾鉛年份測試法給我們帶來了一些驚喜。
Two geologists discovered that about half of the sand from the Grand Canyon was actually once part of the Appalachian Mountains.
兩個地質學家發現大峽谷大約一半的沙子實際上源于阿巴拉契亞山脈。
That's really eye opening news, since the Appalachian Mountain Range is, of course, thousands of kilometers to the east of the Grand Canyon.
這個發現真的令人瞠目結舌，因為大峽谷往東幾千公里才到阿巴拉契亞山脈。
Sounds pretty unbelievable, right?
聽起來很不可思議，是吧？
Of course, the obvious question is how did that sand end up so far west?
的確是這樣，問題是那些沙子怎么能西移那么遠？
The theory is that huge rivers and wind carried the sand west where it mixed in with the sand that was already there.
理論上是這樣認為的：這些沙子被大河沖，狂風刮至大峽谷處匯集、混合并沉淀。
Well, this was a pretty revolutionary finding.
這確實是一個革命性的發現。
Um...and it was basically because of Uranium Lead Dating.
嗯，主要還是鈾鉛年份測試法的應用。
Why?
為什么這樣說？
Well, as everyone in this class should know, we usually look at the grain type within sandstone,
這樣，正如在座的每一個同學應該知道的那樣，我們通常關注沙礫內部的紋理類型，
meaning the actual particles in the sandstone, to determine where it came from.
也就是沙礫里的微粒，來判定它來自哪里。
You can do other things too, like look at the wind or water that brought the grains to their location and figure out which way it was flowing.
我們也有別的方法，比如關注將沙礫帶至該地的風或河流，然后推出它的流向。
But that's only useful up to a point, and that's not what these two geologists did.
然而，這種方法只在一定程度上有用，那兩個地質學家沒有這樣做。
Uranium Lead Dating allowed them to go about it in an entirely different way.
鈾鉛年份測試法給他們提供里全新的方式來推斷沙礫的流向。
What they did was: they looked at the grains of Zircon in the sandstone.
他們做的是：他們研究沙礫里鋯石的紋理。
Zircon is a material that contains radioactive Uranium, which makes it very useful for dating purposes.
鋯石是一種內含放射性鈾的物質，而放射性鈾對年代推算很有幫助。
Zircon starts off as molten magma, the hot larva from volcanoes.
鋯石源于熔巖，一種火山噴發的巖漿。
This magma then crystallizes.
這種巖漿隨后會凝結。
And when Zircon crystallizes, the Uranium inside it begins to change into Lead.
而當鋯石凝結時，鋯石里面的鈾轉化成鉛。
So if you measure the amount of Lead in the Zircon grain, you can figure out when the grain was formed.
所以，如果你測量鋯石里鉛的含量，你可以推算紋理是何時形成的。
After that, you can determine the age of Zircon from different mountain ranges.
之后，你就能從不同的山脈來斷定鋯石的年份。
Once you do that, you can compare the age of the Zircon in the sandstone in your sample to the age of the Zircon in the mountains.
一旦你這樣做，你就可以將樣本沙石里鋯石的年份和山脈里鋯石的年份做比較。
If the age of the Zircon matches the age of one of the mountain ranges, then it means the sandstone actually used to be part of that particular mountain range.
如果樣本沙石里鋯石的年份與山脈里鋯石的年份一致，那就意味著這里的沙石曾經作為這個山脈的一部分而存在。
Is everybody with me on that?
大家同意這個看法嗎？
Good.
很好。
So, in this case, Uranium Lead Dating was used to establish that half of the sandstone in the samples was formed at the same time the granite in the Appalachian mountains was formed.
這樣，鈾鉛年份測試法用于確認樣沙里一半沙石和阿巴拉契亞山脈花崗巖的成形。
So because of this, this new way of doing Uranium Lead Dating, we 've been able to determine that one of our major assumptions about the Grand Canyon was wrong.
所以，正因為這種，這種進行鈾鉛年份測試的新方法，我們有能力判定我們對大峽谷的重大假設之一是錯誤的。
Like I said before, Uranium Lead Dating has been with us for a while.
像我之前說過的那樣，我們已經使用鈾鉛年份測試法有一段時間了。
But, um...until recently, in order to do it, you really had to study many individual grains.
但，嗯，直到最近，要完成這樣的測試，你還真得研究很多（沙礫的）紋理。
And it took a long time before you got results.
當然，要得出結果是需要很長一段時間的。
It just was not very efficient.
這樣的做法其實效率并不高。
And it was not very accurate.
同時，也談不上精確。
But technical advances have cut down on the number of grains you have to study, so you get your results faster.
但是，技術的進步能縮減你需要研究的紋理的數量，這樣你會更快地得到結果。
So I 'll predict that Uranium Lead Dating is going to become an increasingly popular dating method.
我估計鈾鉛年份測試法將成為越發受人歡迎的年份測試法。
There are a few pretty exciting possibilities for Uranium Lead Dating.
在鈾鉛年份測試法里有幾個令人興奮的可能性。
Here is one that comes to mind.
我想起的有這么一個：
You know the theory that earth's continents were once joined together and only split apart relatively recently?
大家都知道地球大陸板塊 “始合近分”的理論吧？
Well, with Uranium Lead Dating, we could prove that more conclusively.
用鈾鉛年份測試法，我們能將這一理論論證得更具總結性。
If they show evidence of once having been joined, that could really tell us a lot about the early history of the planet's geology.
如果能有證據表明“始合”，那些證據就能給我們提供很多地球地質學的早期史料。
