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  • 树木年轮、冰芯和阀门

    Cliff dwellings of Mesa Verde, showcasing ancient architecture in a natural setting.

     

    How could you tell the age of this ruin?
    ::你怎能知道这废墟的年代?

    Mesa Verde in Southwestern Colorado is the site of beautiful cliff dwellings. The people who inhabited these dwellings are long gone. If you go there you will hear the history of the area, complete with dates. How do archeologists know when the people lived here? How do they know the ages of the structures there?  Tree ring  dating is extremely useful for finding the age of ancient structures.
    ::科罗拉多西南部的梅萨维德是美丽的悬崖住所的所在地。 居住在这些住所的人早已消失。 如果你去那里, 你会听到这个地区的历史, 完整的日期。 考古学家如何知道这些人住在这里? 他们怎么知道那里建筑的年代? 树环约会对于寻找古老建筑的年代非常有用。

    Tree Ring Dating
    ::树环日期

    Cut into a tree and you can see its rings. In some locations, the summer growth band is light-colored and the winter band is dark. Each light-dark band represents one  year . You can tell how long the tree lived by counting the number of  tree rings  ( Figure   ). Age dating by tree rings is called  dendrochronology .
    ::切入一棵树, 你可以看到它的戒指。 在有些地方, 夏季生长带是浅色的, 冬季生长带是暗色的。 每个浅色带代表一年。 您可以通过计数树环的数量来判断树的寿命( 图 ) 。 按树环排列的岁数被称为 登年表 。

    Cross-section of a tree trunk showing growth rings used for age dating.

     

    Cross-section showing growth rings.
    ::交叉显示生长环。

    You can tell other things from tree rings too. In a good year a tree will produce a wide ring. A summer  drought  will produce a smaller ring. These variations will appear in all trees in a region. The same pattern can be found in all the trees in the area. This pattern helps scientist to identify a particular time period.
    ::您也可以从树环中告诉其它东西。 在好的一年中, 树将产生一个宽的环。 夏季干旱将产生一个较小的环。 这些变化将出现在一个区域的所有树上。 该地区所有树上都可以看到同样的模式。 这个模式有助于科学家确定一个特定的时间段 。

    Scientists have records of tree rings going back over the past 2,000 years. By matching up patterns they can tell when a tree (or a piece of wood from one) lived. Wood fragments from old buildings and ancient ruins can be age dated. The outermost ring gives the date when the tree died.
    ::科学家们记录了过去2000年的树环。 通过匹配图案,他们可以辨别一棵树(或一棵木头)在什么时候生存。旧建筑和古老废墟中的木块可以追溯到年代。最外层的木环给出了树死亡的日期。

    Ice Cores
    ::冰芯

    Other processes create yearly layers that can be used for dating. On a  ,  snow  falls in winter. In summer, dust accumulates. This leads to a snow-dust annual pattern. This pattern can be seen down into the ice ( Figure   ). Scientists drill deep into ice sheets.  Ice cores  can be hundreds of meters long. The ice cores show how the environment has changed. Gas bubbles in the ice can be analyzed to show how atmospheric gases have changed. This can yield clues about  climate . Long ice cores have allowed scientists to create a record of  polar climate  going back hundreds of thousands of years.
    ::其它过程每年生成可用于约会的层层。 在冬天下雪, 冬季下雪。 夏季, 灰尘会累积。 这导致雪尘的年度模式。 这种模式可以从冰层中看出( 图表 ) 。 科学家钻入冰层深处。 冰芯可以长数百米。 冰芯可以显示环境的变化。 冰芯可以分析冰中的气泡, 以显示大气气体是如何变化的。 这可以产生关于气候的线索。 长期的冰芯可以让科学家创造出数十万年的极地气候记录。

    Cross-section of an ice core displaying annual layers of snow and dust.

     

    Ice core section showing annual layers.
    ::显示年度层次的冰核心部分。

    Varves
    ::变形

    Lake   sediments  also have an annual pattern. This is easy to see in lakes that are located at the end of glaciers. The glacier melts rapidly in the summer. This produces a thick deposit of sediment in the lake. Thin, clay-rich layers are  deposited  in the winter. The resulting layers are called  varves . Varves give scientists clues about past climate conditions ( Figure   ). A warm summer might result in a very thick sediment layer. A cooler summer might yield a thinner layer. Like tree rings, these patterns can be used to identify time periods.
    ::湖泊沉积物也具有年度模式。 在冰川尽头的湖泊中,这很容易看到。冰川在夏季迅速融化。这在湖中造成厚厚的沉积物沉积。薄的、含粘土的层沉积在冬季。由此形成的层层被称为弧形。多谷为科学家们提供了过去气候条件的线索(图 )。温暖的夏季可能会形成非常厚厚的沉积物层。较冷的夏季可能会形成较薄的层。像树圈一样,这些模式可以用来确定时间段。

    Close-up of ancient varve sediments showing alternating layers of varying thicknesses.

     

    Ancient varve sediments in a rock outcrop.
    ::岩层外的古代峡谷沉积层

    Summary
    ::摘要

    • Where conditions vary seasonally, trees develop distinctive rings. Ice contains more or less dust. Lake sediments show more or less clay.
      ::如果季节性条件不同,树木会形成独特的环状,冰或多或少含有灰尘,湖中沉积物显示的泥土或多或少。
    • Tree rings, ice cores, and varves indicate the environmental conditions at the time they were made.
      ::树木环、冰芯和花岗岩表示其形成时的环境状况。
    • The distinctive patterns of tree rings, ice cores, and varves go back thousands of years. They can be used to determine the time they were made.
      ::树环、冰芯和花岗岩的独特模式可以追溯到数千年前。它们可以用来确定它们造出来的时间。

    Review
     ::回顾

    1. Why are these three dating methods considered absolute age dating?
      ::为什么这三种约会方法都被视为绝对年龄约会?
    1. Describe how tree rings indicate time. Do the same for ice cores and varves.
      ::描述树环如何显示时间。 对于冰芯和花瓶, 也做同样的事情 。
    1. Describe how tree rings, ice cores, and varves indicate what was going on in the environment when they formed.
      ::描述树环、冰芯和花冠如何表明它们形成时在环境中发生的情况。

    Explore More
    ::探索更多

    Use the resources below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    1. What do annual tree rings tell scientists?
      ::一年一度的树环告诉科学家什么?
    1. What can be learned from tree rings?
      ::从树圈可以学到什么?
    1. What do tree rings indicate about the lost colony of Roanoke, Virginia?
      ::树圈表示 失去的罗阿诺克殖民地 维吉尼亚州是什么?
    1. What type of trees do scientists look for? Why?
      ::科学家们找哪类树?
    1. What is trapped in the ice cores and when it it from?
      ::冰芯中有什么被困在冰芯里? 冰芯是什么时候产的?
    1. How long have ice cores been studied?
      ::冰芯研究多久了?
    1. What can be learned from ice cores?
      ::从冰芯中可以学到什么?
    1. What circumstances make the best ice cores? What is a good location to obtain cores like this?
      ::什么样的环境能让冰芯成为最好的冰芯?什么是获得这种岩芯的好地方?
    1. How much would sea level rise if the Greenland ice sheet melted?
      ::如果格陵兰冰盖融化,海平面会升高多少?