关于托福听力课程的自然科学类，常常会出现一个名词：Plate Tectonics板块运动/地壳构造论。可能许多考生都会对这个学说感到熟悉又陌生，接下来给大家聊聊我们脚下的土地到底是怎么运动的。
Plate tectonics is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large of tectonic plates which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift. Earth's lithosphere is broken into seven or eight major plates and many minor plates. Earthquakes,and oceanic trench formation occur along these plate boundaries. Tectonic plates are composed of the continental plate and the denser oceanic plate. If two plates collide, the denser one will subduct beneath the less dense one. The three different types of plate boundaries are divergent boundaries, convergent boundaries, and transform boundaries.
板块构造学是一个已经被普遍接受的科学理论，它认为地球的岩石圈lithosphere是由许多自大约 34 亿年前以来一直在缓慢移动的大型构造板块组成。这个模型主要是建立在大陆漂移continental drift的概念基础之上。地球的岩石圈共被分成7至8个主要板块和许多小板块，在这些板块相遇的地方，我们经常能够见到地震、火山、造山和海沟形成等活动。构造板块是通过大陆板块和密度更大的海洋板块一起组成。当两个板块碰撞时，密度较大的板块将俯冲到密度较小的板块下面。地球上一共存在三种主要的板块边界类型，分别为扩张边界、聚合边界和转换边界。
分离型边界 Divergent Boundary
Divergent boundaries occur where two plates slide apart from each other. At zones of ocean-to-ocean rifting, the ocean basin expands. At zones of continent-to-continent rifting, divergent boundaries may cause new ocean basin to form as the continent splits, spreads, the central rift collapses, and ocean fills the basin.
The most significant example of divergent boundaries is the East African Rift.
扩张边界出现在两个板块往相反方向移动的地方。在海洋间的裂谷带，海底扩张形成了不同的边界。随着海洋板块的分裂，一道洋脊在扩张中心形成，海洋盆地也逐渐扩大。在大陆间的裂谷带，随着大陆分裂、扩张，中央裂谷渐渐塌陷，逐渐的形成了新的海洋。扩张边界最显著的例子便是东非大裂谷。 |
