第九课翻译.doc

LESSON 9 HISTORICAL PERSPECTIVE IN PALEONTOLOGY Time is what sets geology apart from most of the other sciences, and an appreciation of the immensity of geologic time is fundamental to understanding both the physical and biologic history of our planet. Most people have difficulty comprehending geologic time because they tend to view time from the perspective of their own existence. 时间是什么使地质有别于其他科学和地质时间的无垠的升值是理解的基础物理和生物地球的历史。大多数人很难理解地质时间,因为他们倾向于把时间从他们自己的角度存在。 Ancient history is what occurred hundreds or even thousands of years ago, but when geologists talk in terms of ancient geologic history, they are referring to events that happened millions or even billions of years ago! (See Perspective 2.1.)古代历史是发生数百甚至数千年前,但是当地质学家说的古老的地质历史,他们是指事件发生数百万甚至数十亿年前!(见2.1角度。) 　　　 Geologists use two different frames of reference when speaking of geologic time. Relative dating involves placing geologic events in a sequential order as determined from their position in the rock record. 地质学家使用两个不同的地质时期的参考帧说话的时候。相对约会需要按顺序放置地质事件决定从他们的立场在岩石记录。 Relative dating will not tell us how long ago a particular event occurred, only that one event preceded another. The various principles used to determine relative dating were discovered hundreds of years ago and since then have been used to construct the relative geologic time scale (Figure 2.1). These principles are still widely used today.相对约会不会告诉我们多久以前一个特定事件发生时,只有这一个事件之前另一个。各种原则用于确定相对约会被发现几百年前和自那时以来一直用于构造相对地质时间尺度(图2.1)。这些原则是今天仍然广泛使用。 　　　 Absolute dating results in specific dates for rock units or events expressed in years before the present. Radiometric dating is the most common method of obtaining absolute-age dates. 绝对年代测定结果在特定日期岩石单位或事件表达的年前。放射性定年法是最常见的方法获得绝对年代日期。 Such dates are calculated from the natural rates of decay of various radioactive elements present in trace amounts in some rocks. It was not until the discovery of radioactivity near the end of the nineteenth century that absolute ages could be accurately applied to the relative geologic