Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth’s surface; on the contrary, many of them lie deep in the interior of a plate. Most of the hot spots move only slowly, and in some cases the movement of the plates past them has left trails of dead volcanoes. The hot spots and their volcanic trails are milestones that mark the passage of the plates.
That the plates are moving is not beyond dispute. Africa and South America, for example, are moving away from each other as new material is injected into the sea floor between them. The complementary coastlines and certain geological features that seem to span the ocean are reminders of where the two continents were once joined. The relative motion of the plates carrying these continents has been constructed in detail, but the motion of one plate with respect to another cannot readily be translated into motion with respect to the earth’s interior. It is not possible to determine whether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it. Hot spots, anchored in the deeper layers of the earth, provide the measuring instruments needed to resolve the question. From an analysis of the hot spot population it appears that the African plate is stationary and that it has not moved during the past 30 million years.
The significance of hot spots is not confined to their role as a frame of reference. It now appears that they also have an important influence on the geophysical processes that propel the plates across the globe. When a continental plate come to rest over a hot spot, the material rising from deeper layer creates a broad dome. As the dome grows, it develops seed fissures(cracks); in at least a few cases the continent may break entirely along some of these fissures, so that the hot spot initiates the formation of a new ocean. Thus just as earlier theories have explained the mobility of the continents, so hot spots may explain their mutability (inconstancy).
Coastlinen n. 海岸线
例句：Unrestricted hotel development have ruined the coastline无限制地发展饭店已经使沿海地区遭到破坏。.
Continent n. 大陆, 洲a. 自制的
派生：continence, continency n. 克己;自制 continental a. 大陆的 continently ad. 自制地
例句：Africa is a very large continent非洲是一块非常大的大陆。.
词组：the continent of Asia亚细亚大陆
反义词：incontinent; island; isle
Drifting adj. 漂流的, 飘动的
例句：He is drifting through life. 他随波逐流地过日子。
Determine vt. 决定, 决心vi. 决定, 决心
派生：determined a. 坚决地 determiner n. 限定词
例句：A rather elaborate analysis was required to determine the cross-over values. 要求相当精确地分析才能确定其交换值。
词组：be determined to do sth. 决心做某事determine on/determine upon 决定determine sb. against sth./determine sb. to do sth. 使某人决定不做某事
Entirely ad. 完全, 全然, 一概
例句：I meant to mail the letter, but it entirely slipped my memory. 我本来准备发这封信的，却完全给忘掉了。
同义词：altogether completely exclusively fully solely thoroughly totally wholly
Frame n. 框, 结构, 体格vt. 构成, 设计, 制定, 使适合, 陷害
例句：He had a deep, resonant voice, fitted to his massive frame. 他的嗓音低沉，带着回音，同他魁梧的体格非常相配。
词组：picture frame 画框, 相框 (=sheriffs picture frame)绞架be not framed for 不适于; 经不起; 受不住out of frame 纷乱, 无秩序frame of mind 心情, 心境frame to oneself 想象frame up (美俚)诬陷frame well 有才能, 有希望
同义词：arrange body border bound build construct design devise edge figure form make plan put together skeleton support trim
Geologist n. 地质学家;地质学者
例句：One was blue, and a geologist; one was a horsewoman and smoked cigars. 她们中间一个是女才子，地质学家;一个是女骑手，还会吸雪茄。
Geophysical a. 地球物理学的
例句：The method has proved more and more to be of very great geophysical significance. 这个方法在地球物理学上的重要性越来越明显。
Interior n. 内部, 内政a. 内部的, 心灵的, 内地的, 内政的
例句：He discussed the propagation of waves through the earth's interior. 他探讨了地震波在地球内部的传播。
词组：an interior city内地城市
同义词：core heart inner inside middle nucleus
Milestone n. 里程碑, 里程石, 里程标
例句：This Games will be a milestone in Olympic history, and in the history of China. 北京的奥运会将成为奥林匹克历史和中国历史中的一个里程碑。
Mobility n. 可动性, 流动性, 机动性
例句：There has been a tremendous increase in mobility. 人才流动已经有了大幅度增加。
Mutability n. 易变性, 性情不定
词组：mutability of human affairs人世沧桑
Reminder n. 提醒的人, 暗示
例句：They need reminders人们需要经常被提醒一下，以便停下来关照一下家庭生活，并向心上人表达关爱。 to slow down to the pace of family life and show their care for loved ones.
词组：a reminder slip催询单a reminder tray意见箱a gentle reminder暗示
Readily ad. 迅速地, 轻易地, 乐意地
例句：He readily agreed to help us. 他欣然同意帮助我们。
Scattered a. 分散的, 散乱的
例句：Factories should be scattered instead of being concentrated in a single area. 工厂应分散布局而不应集中在一个地区。
词组：scattered set无核集scattered sheaf散射层
Significance n. 重要性, 意义, 意味
例句：Most leaders'vanity causes them to exaggerate their own significance. 绝大多数领导人出于虚荣心往往喜欢夸大他们自己的重要地位。
词组：of no (little) significance 无关紧要的
同义词：connotation consequence drift effect gist implication importance meaning substance2015年考研英语：英语Ⅰ和英语Ⅱ题型差异详解