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]巖石圈)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.
板塊結構與海床擴展
板塊結構理論描述巖石圈的運動。巖石圈是相對堅硬的地球外層，包括全部地殼和部分地幔。
巖石圈被劃分為幾十個大小不同形狀各異的板塊，一般而言這些板塊都處于相對運動之中。一道中海脊是板塊之間的邊界，在那里新的巖石圈的物質從下部注入。
當板塊從中海脊脫離時，它們滑向在巖石圈基部較易變形的地層上。因為地球的大小本質上是不
變的，只有同等數(shù)量的巖石圈物質在其它地方被吞沒，新的巖石圈才能生成。銷毀舊巖石
圈的地方形成另外一種板塊邊界：一塊潛沒的區(qū)域。在這里，一塊板塊潛沒到另一板塊的邊緣之下并結合入地幔之中。
兩種板塊邊界均與地層系統(tǒng)、地震以及火山活動有關，但在兩種邊界處觀察到的諸般地質活動卻迥然不同。海床擴展說實際上早于板塊結構理論。在
20世紀60年代它的理論雛形中，描述了海底的生成和毀滅，但沒有詳細介紹堅硬的巖石圈板塊。這個假定不久之后為發(fā)現(xiàn)所證實。
該發(fā)現(xiàn)表明地球磁場周期性的逆轉被記錄在海洋地殼中。當巖漿從中海脊下涌起的時候，巖漿中的磁鐵礦物質按地磁場的方向被磁化。巖
漿冷卻并凝固下來后，地磁場的方向和磁極被保留在磁化了的火山巖中。磁場的逆轉形成一系列與斷層軸線平行的條形磁區(qū)。
這樣海洋殼就扮演了磁帶的角色，記錄下可以鑒定時間的地磁場的歷史。條形磁區(qū)的寬度表明了海底擴展的速度。
1 lithosphere
n.陸界，巖石圈
參考例句：
The hydrosphere and the lithosphere together form the Earth's surface.水圈與巖石圈一起形成地球的表面。
They slide on a more yielding layer at the base of lithosphere.它們在巖石圈底部更柔軟的一層滑動。
2 rigid
adj.嚴格的，死板的；剛硬的，僵硬的
參考例句：
She became as rigid as adamant.她變得如頑石般的固執(zhí)。
The examination was so rigid that nearly all aspirants were ruled out.考試很嚴，幾乎所有的考生都被淘汰了。
3 underlying 5fyz8c
adj.在下面的，含蓄的，潛在的
參考例句：
The underlying theme of the novel is very serious.小說隱含的主題是十分嚴肅的。
This word has its underlying meaning.這個單詞有它潛在的含義。
4 mantle
n.斗篷，覆罩之物，罩子；v.罩住，覆蓋，臉紅
參考例句：
The earth had donned her mantle of brightest green.大地披上了蒼翠欲滴的綠色斗篷。
The mountain was covered with a mantle of snow.山上覆蓋著一層雪。
5 ridge
n.山脊；鼻梁；分水嶺
參考例句：
We clambered up the hillside to the ridge above.我們沿著山坡費力地爬上了山脊。
The infantry were advancing to attack the ridge.步兵部隊正在向前挺進攻打山脊。
6 lithospheric
adj.巖石圈的
參考例句：
The existence and movement of large lithospheric plates seems well established. 巨大巖石圈板塊的存在與位移似乎已完全確定了。 來自辭典例句
In the case of sufficiently young chasmic basins high heat flows are due to lithospheric cooling. 這種相當年輕的裂陷盆地的高熱流是由巖石圈冷卻所引起的。 來自辭典例句
7 diverge
v.分叉，分歧，離題，使...岔開，使轉向
參考例句：
This is where our opinions diverge from each other.這就是我們意見產生分歧之處。
Don't diverge in your speech.發(fā)言不要離題。
8 essentially
adv.本質上，實質上，基本上
參考例句：
Really great men are essentially modest.真正的偉人大都很謙虛。
She is an essentially selfish person.她本質上是個自私自利的人。
9 ridges
n.脊( ridge的名詞復數(shù) )；山脊；脊狀突起；大氣層的)高壓脊
參考例句：
The path winds along mountain ridges. 峰回路轉。
Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，這大概可以算是天經(jīng)地義第一條了。
10 geologic
adj.地質的
參考例句：
The Red Sea is a geologic continuation of the valley.紅海就是一個峽谷在地質上的繼續(xù)發(fā)展。
Delineation of channels is the first step of geologic evaluation.勾劃河道的輪廓是地質解譯的第一步。
11 specify
vt.指定，詳細說明
參考例句：
We should specify a time and a place for the meeting.我們應指定會議的時間和地點。
Please specify what you will do.請你詳述一下你將做什么。
12 substantiated
v.用事實支持（某主張、說法等），證明，證實( substantiate的過去式和過去分詞 )
參考例句：
The results of the tests substantiated his claims. 這些檢驗的結果證實了他的說法。
The statement has never been substantiated. 這一陳述從未得到證實。 來自《現(xiàn)代漢英綜合大詞典》
13 afterward
adv.后來；以后
參考例句：
Let's go to the theatre first and eat afterward. 讓我們先去看戲，然后吃飯。
Afterward,the boy became a very famous artist.后來，這男孩成為一個很有名的藝術家。
14 ferromagnetic
adj.鐵磁的, 鐵磁體
參考例句：
Materials which have magnetic properties similar to iron are ferromagnetic.具有類似于鐵那樣的磁性的材料就是鐵磁物質。
It is sometimes difficult to draw the line separating ferromagnetic from paramagnetic substances.嚴格區(qū)別鐵磁性與順磁性物質有時是很困難的。
15 solidifies
（使）成為固體，（使）變硬，（使）變得堅固( solidify的第三人稱單數(shù) )； 使團結一致； 充實，鞏固； 具體化
參考例句：
Jelly solidifies as it gets cold. 肉凍冷卻就凝固。
It is stirred with 10%sodium carbonate solution(50ml)and then with water (50ml), after which It'solidifies. 與10％碳酸鈉溶液（50毫升）混合攪拌，然后再用50毫升水混合攪拌，從而析出固體。
16 volcanic
adj.火山的；象火山的；由火山引起的
參考例句：
There have been several volcanic eruptions this year.今年火山爆發(fā)了好幾次。
Volcanic activity has created thermal springs and boiling mud pools.火山活動產生了溫泉和沸騰的泥漿池。
17 axis
n.軸，軸線，中心線；坐標軸，基準線
參考例句：
The earth's axis is the line between the North and South Poles.地軸是南北極之間的線。
The axis of a circle is its diameter.圓的軸線是其直徑。
18 rift
n.裂口，隙縫，切口；v.裂開，割開，滲入
參考例句：
He was anxious to mend the rift between the two men.他急于彌合這兩個人之間的裂痕。
The sun appeared through a rift in the clouds.太陽從云層間隙中冒出來。
19 recording
n.錄音，記錄
參考例句：
How long will the recording of the song take?錄下這首歌得花多少時間？
I want to play you a recording of the rehearsal.我想給你放一下彩排的錄像。
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.
板塊結構與海床擴展
板塊結構理論描述巖石圈的運動。巖石圈是相對堅硬的地球外層，包括全部地殼和部分地幔。
巖石圈被劃分為幾十個大小不同形狀各異的板塊，一般而言這些板塊都處于相對運動之中。一道中海脊是板塊之間的邊界，在那里新的巖石圈的物質從下部注入。
當板塊從中海脊脫離時，它們滑向在巖石圈基部較易變形的地層上。因為地球的大小本質上是不
變的，只有同等數(shù)量的巖石圈物質在其它地方被吞沒，新的巖石圈才能生成。銷毀舊巖石
圈的地方形成另外一種板塊邊界：一塊潛沒的區(qū)域。在這里，一塊板塊潛沒到另一板塊的邊緣之下并結合入地幔之中。
兩種板塊邊界均與地層系統(tǒng)、地震以及火山活動有關，但在兩種邊界處觀察到的諸般地質活動卻迥然不同。海床擴展說實際上早于板塊結構理論。在
20世紀60年代它的理論雛形中，描述了海底的生成和毀滅，但沒有詳細介紹堅硬的巖石圈板塊。這個假定不久之后為發(fā)現(xiàn)所證實。
該發(fā)現(xiàn)表明地球磁場周期性的逆轉被記錄在海洋地殼中。當巖漿從中海脊下涌起的時候，巖漿中的磁鐵礦物質按地磁場的方向被磁化。巖
漿冷卻并凝固下來后，地磁場的方向和磁極被保留在磁化了的火山巖中。磁場的逆轉形成一系列與斷層軸線平行的條形磁區(qū)。
這樣海洋殼就扮演了磁帶的角色，記錄下可以鑒定時間的地磁場的歷史。條形磁區(qū)的寬度表明了海底擴展的速度。
1 lithosphere
n.陸界，巖石圈
參考例句：
The hydrosphere and the lithosphere together form the Earth's surface.水圈與巖石圈一起形成地球的表面。
They slide on a more yielding layer at the base of lithosphere.它們在巖石圈底部更柔軟的一層滑動。
2 rigid
adj.嚴格的，死板的；剛硬的，僵硬的
參考例句：
She became as rigid as adamant.她變得如頑石般的固執(zhí)。
The examination was so rigid that nearly all aspirants were ruled out.考試很嚴，幾乎所有的考生都被淘汰了。
3 underlying 5fyz8c
adj.在下面的，含蓄的，潛在的
參考例句：
The underlying theme of the novel is very serious.小說隱含的主題是十分嚴肅的。
This word has its underlying meaning.這個單詞有它潛在的含義。
4 mantle
n.斗篷，覆罩之物，罩子；v.罩住，覆蓋，臉紅
參考例句：
The earth had donned her mantle of brightest green.大地披上了蒼翠欲滴的綠色斗篷。
The mountain was covered with a mantle of snow.山上覆蓋著一層雪。
5 ridge
n.山脊；鼻梁；分水嶺
參考例句：
We clambered up the hillside to the ridge above.我們沿著山坡費力地爬上了山脊。
The infantry were advancing to attack the ridge.步兵部隊正在向前挺進攻打山脊。
6 lithospheric
adj.巖石圈的
參考例句：
The existence and movement of large lithospheric plates seems well established. 巨大巖石圈板塊的存在與位移似乎已完全確定了。 來自辭典例句
In the case of sufficiently young chasmic basins high heat flows are due to lithospheric cooling. 這種相當年輕的裂陷盆地的高熱流是由巖石圈冷卻所引起的。 來自辭典例句
7 diverge
v.分叉，分歧，離題，使...岔開，使轉向
參考例句：
This is where our opinions diverge from each other.這就是我們意見產生分歧之處。
Don't diverge in your speech.發(fā)言不要離題。
8 essentially
adv.本質上，實質上，基本上
參考例句：
Really great men are essentially modest.真正的偉人大都很謙虛。
She is an essentially selfish person.她本質上是個自私自利的人。
9 ridges
n.脊( ridge的名詞復數(shù) )；山脊；脊狀突起；大氣層的)高壓脊
參考例句：
The path winds along mountain ridges. 峰回路轉。
Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，這大概可以算是天經(jīng)地義第一條了。
10 geologic
adj.地質的
參考例句：
The Red Sea is a geologic continuation of the valley.紅海就是一個峽谷在地質上的繼續(xù)發(fā)展。
Delineation of channels is the first step of geologic evaluation.勾劃河道的輪廓是地質解譯的第一步。
11 specify
vt.指定，詳細說明
參考例句：
We should specify a time and a place for the meeting.我們應指定會議的時間和地點。
Please specify what you will do.請你詳述一下你將做什么。
12 substantiated
v.用事實支持（某主張、說法等），證明，證實( substantiate的過去式和過去分詞 )
參考例句：
The results of the tests substantiated his claims. 這些檢驗的結果證實了他的說法。
The statement has never been substantiated. 這一陳述從未得到證實。 來自《現(xiàn)代漢英綜合大詞典》
13 afterward
adv.后來；以后
參考例句：
Let's go to the theatre first and eat afterward. 讓我們先去看戲，然后吃飯。
Afterward,the boy became a very famous artist.后來，這男孩成為一個很有名的藝術家。
14 ferromagnetic
adj.鐵磁的, 鐵磁體
參考例句：
Materials which have magnetic properties similar to iron are ferromagnetic.具有類似于鐵那樣的磁性的材料就是鐵磁物質。
It is sometimes difficult to draw the line separating ferromagnetic from paramagnetic substances.嚴格區(qū)別鐵磁性與順磁性物質有時是很困難的。
15 solidifies
（使）成為固體，（使）變硬，（使）變得堅固( solidify的第三人稱單數(shù) )； 使團結一致； 充實，鞏固； 具體化
參考例句：
Jelly solidifies as it gets cold. 肉凍冷卻就凝固。
It is stirred with 10%sodium carbonate solution(50ml)and then with water (50ml), after which It'solidifies. 與10％碳酸鈉溶液（50毫升）混合攪拌，然后再用50毫升水混合攪拌，從而析出固體。
16 volcanic
adj.火山的；象火山的；由火山引起的
參考例句：
There have been several volcanic eruptions this year.今年火山爆發(fā)了好幾次。
Volcanic activity has created thermal springs and boiling mud pools.火山活動產生了溫泉和沸騰的泥漿池。
17 axis
n.軸，軸線，中心線；坐標軸，基準線
參考例句：
The earth's axis is the line between the North and South Poles.地軸是南北極之間的線。
The axis of a circle is its diameter.圓的軸線是其直徑。
18 rift
n.裂口，隙縫，切口；v.裂開，割開，滲入
參考例句：
He was anxious to mend the rift between the two men.他急于彌合這兩個人之間的裂痕。
The sun appeared through a rift in the clouds.太陽從云層間隙中冒出來。
19 recording
n.錄音，記錄
參考例句：
How long will the recording of the song take?錄下這首歌得花多少時間？
I want to play you a recording of the rehearsal.我想給你放一下彩排的錄像。