英语美文背诵 Plate Tectonics and Sea-floor Sprea

Plate Tectonics and Sea-floor Spreading

The theory of plate tectonics describes the motions of the lithosphere¹, the comparatively rigid² outer layer of the Earth that includes all the crust and part of the underlying³ mantle⁴. The lithosphere(n.[地]岩石圈)is divided into a few dozen plates of various sizes and shapes, in general the plates are in motion with respect to one another. A mid-ocean ridge⁵ is a boundary between plates where new lithospheric⁶ material is injected from below. As the plates diverge⁷ from a mid-ocean ridge they slide on a more yielding layer at the base of the lithosphere.

Since the size of the Earth is essentially⁸ constant, new lithosphere can be created at the mid-ocean ridges⁹ only if an equal amount of lithospheric material is consumed elsewhere. The site of this destruction is another kind of plate boundary: a subduction zone. There one plate dives under the edge of another and is reincorporated into the mantle. Both kinds of plate boundary are associated with fault systems, earthquakes and volcanism, but the kinds of geologic¹⁰ activity observed at the two boundaries are quite different.

The idea of sea-floor spreading actually preceded the theory of plate tectonics. In its original version, in the early 1960’s, it described the creation and destruction of the ocean floor, but it did not specify¹¹ rigid lithospheric plates. The hypothesis was substantiated¹² soon afterward¹³ by the discovery that periodic reversals of the Earth’s magnetic field are recorded in the oceanic crust. As magma rises under the mid-ocean ridge, ferromagnetic¹⁴ minerals in the magma become magnetized in the direction of the magma become magnetized in the direction of the geomagnetic field. When the magma cools and solidifies¹⁵, the direction and the polarity of the field are preserved in the magnetized volcanic¹⁶ rock. Reversals of the field give rise to a series of magnetic stripes running parallel to the axis¹⁷ of the rift¹⁸. The oceanic crust thus serves as a magnetic tape recording¹⁹ of the history of the geomagnetic field that can be dated independently; the width of the stripes indicates the rate of the sea-floor spreading.

板块结构与海床扩展

板块结构理论描述岩石圈的运动。岩石圈是相对坚硬的地球外层，包括全部地壳和部分地幔。

岩石圈被划分为几十个大小不同形状各异的板块，一般而言这些板块都处于相对运动之中。一道中海脊是板块之间的边界，在那里新的岩石圈的物质从下部注入。

当板块从中海脊脱离时，它们滑向在岩石圈基部较易变形的地层上。因为地球的大小本质上是不

变的，只有同等数量的岩石圈物质在其它地方被吞没，新的岩石圈才能生成。销毁旧岩石

圈的地方形成另外一种板块边界：一块潜没的区域。在这里，一块板块潜没到另一板块的边缘之下并结合入地幔之中。

两种板块边界均与地层系统、地震以及火山活动有关，但在两种边界处观察到的诸般地质活动却迥然不同。海床扩展说实际上早于板块结构理论。在

20世纪60年代它的理论雏形中，描述了海底的生成和毁灭，但没有详细介绍坚硬的岩石圈板块。这个假定不久之后为发现所证实。

该发现表明地球磁场周期性的逆转被记录在海洋地壳中。当岩浆从中海脊下涌起的时候，岩浆中的磁铁矿物质按地磁场的方向被磁化。岩

浆冷却并凝固下来后，地磁场的方向和磁极被保留在磁化了的火山岩中。磁场的逆转形成一系列与断层轴线平行的条形磁区。

这样海洋壳就扮演了磁带的角色，记录下可以鉴定时间的地磁场的历史。条形磁区的宽度表明了海底扩展的速度。

1 lithosphere   

n.陆界，岩石圈

参考例句：

• The hydrosphere and the lithosphere together form the Earth's surface.水圈与岩石圈一起形成地球的表面。
• They slide on a more yielding layer at the base of lithosphere.它们在岩石圈底部更柔软的一层滑动。

2 rigid   

adj.严格的，死板的；刚硬的，僵硬的

参考例句：

• She became as rigid as adamant.她变得如顽石般的固执。
• The examination was so rigid that nearly all aspirants were ruled out.考试很严，几乎所有的考生都被淘汰了。

3 underlying   

adj.在下面的，含蓄的，潜在的

参考例句：

• The underlying theme of the novel is very serious.小说隐含的主题是十分严肃的。
• This word has its underlying meaning.这个单词有它潜在的含义。

4 mantle   

n.斗篷，覆罩之物，罩子；v.罩住，覆盖，脸红

参考例句：

• The earth had donned her mantle of brightest green.大地披上了苍翠欲滴的绿色斗篷。
• The mountain was covered with a mantle of snow.山上覆盖着一层雪。

5 ridge   

n.山脊；鼻梁；分水岭

参考例句：

• We clambered up the hillside to the ridge above.我们沿着山坡费力地爬上了山脊。
• The infantry were advancing to attack the ridge.步兵部队正在向前挺进攻打山脊。

6 lithospheric   

adj.岩石圈的

参考例句：

• The existence and movement of large lithospheric plates seems well established. 巨大岩石圈板块的存在与位移似乎已完全确定了。 来自辞典例句
• In the case of sufficiently young chasmic basins high heat flows are due to lithospheric cooling. 这种相当年轻的裂陷盆地的高热流是由岩石圈冷却所引起的。 来自辞典例句

7 diverge   

v.分叉，分歧，离题，使...岔开，使转向

参考例句：

• This is where our opinions diverge from each other.这就是我们意见产生分歧之处。
• Don't diverge in your speech.发言不要离题。

8 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。

9 ridges   

n.脊( ridge的名词复数 )；山脊；脊状突起；大气层的)高压脊

参考例句：

• The path winds along mountain ridges. 峰回路转。
• Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，这大概可以算是天经地义第一条了。

10 geologic   

adj.地质的

参考例句：

• The Red Sea is a geologic continuation of the valley.红海就是一个峡谷在地质上的继续发展。
• Delineation of channels is the first step of geologic evaluation.勾划河道的轮廓是地质解译的第一步。

11 specify   

vt.指定，详细说明

参考例句：

• We should specify a time and a place for the meeting.我们应指定会议的时间和地点。
• Please specify what you will do.请你详述一下你将做什么。

12 substantiated   

v.用事实支持（某主张、说法等），证明，证实( substantiate的过去式和过去分词 )

参考例句：

• The results of the tests substantiated his claims. 这些检验的结果证实了他的说法。
• The statement has never been substantiated. 这一陈述从未得到证实。 来自《现代汉英综合大词典》

13 afterward   

adv.后来；以后

参考例句：

• Let's go to the theatre first and eat afterward. 让我们先去看戏，然后吃饭。
• Afterward,the boy became a very famous artist.后来，这男孩成为一个很有名的艺术家。

14 ferromagnetic   

adj.铁磁的, 铁磁体

参考例句：

• Materials which have magnetic properties similar to iron are ferromagnetic.具有类似于铁那样的磁性的材料就是铁磁物质。
• It is sometimes difficult to draw the line separating ferromagnetic from paramagnetic substances.严格区别铁磁性与顺磁性物质有时是很困难的。

15 solidifies   

（使）成为固体，（使）变硬，（使）变得坚固( solidify的第三人称单数 )； 使团结一致； 充实，巩固； 具体化

参考例句：

• Jelly solidifies as it gets cold. 肉冻冷却就凝固。
• It is stirred with 10%sodium carbonate solution(50ml)and then with water (50ml), after which It'solidifies. 与10％碳酸钠溶液（50毫升）混合搅拌，然后再用50毫升水混合搅拌，从而析出固体。

16 volcanic   

adj.火山的；象火山的；由火山引起的

参考例句：

• There have been several volcanic eruptions this year.今年火山爆发了好几次。
• Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。

17 axis   

n.轴，轴线，中心线；坐标轴，基准线

参考例句：

• The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
• The axis of a circle is its diameter.圆的轴线是其直径。

18 rift   

n.裂口，隙缝，切口；v.裂开，割开，渗入

参考例句：

• He was anxious to mend the rift between the two men.他急于弥合这两个人之间的裂痕。
• The sun appeared through a rift in the clouds.太阳从云层间隙中冒出来。

19 recording   

n.录音，记录

参考例句：

• How long will the recording of the song take?录下这首歌得花多少时间？
• I want to play you a recording of the rehearsal.我想给你放一下彩排的录像。