高中(北师大版)英语必修3课件：Unit 7 The sea7单元话题阅读
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When an ocean plate bumps into a land plate，the less dense land plate floats over the ocean one.The ocean floor gets pushed under，and its salty rocks，along with shells and bones，are lost deep within Earth.
•7、风声雨声读书声，声声入耳；家事国事天下事，事事关心。2021/10/262021/10/26October 26, 2021 •8、先生不应该专教书，他的责任是教人做人；学生不应该专读书，他的责任是学习人生之道。2021/10/262021/10/262021/10/262021/10/26
Pick up a clamshell (蛤壳) and weigh it in your hand.It is heavy.All creatures need sodium (钠)) to live and most need calcium to build bones and shells.The clam，like all sea creatures，gets its sodium and calcium from seawater.When creatures die，their salt is locked up in bones and shells，which drop to the bottom of the sea.
The outer hard crust of Earth is made up of a dozen or so hard plates that drift (漂流) on extremely hot，soft rock like floating islands on a sea.The heat within Earth is not the same everywhere and the plates move due to the heat.
Reactions between seawater and rocks are not just one way.Sea salt not only dissolves (溶解) from rocks；it also reacts with the rocks of the ocean crust (地 壳) and volcanic lava (熔岩)．The reactions take some of the salts in seawater away from the sea.
So，that’s why the seas are salty but don’t get any saltier.
谢谢观看！
•1、使教育过程成为一种艺术的事业。 •2、教师之为教，不在全盘授予，而在相机诱导。2021/10/262021/10/262021/10/2610/26/2021 7:56:11 PM •3、一年之计，莫如树谷；十年之计，莫如树木；终身之计，莫如树人4、智力教育就是要扩大人的求知范围 •5、教育是一个逐步发现自己无知的过程。 •6、要经常培养开阔的胸襟，要经常培养知识上诚实的习惯，而且要经常学习向自己的思想负责任。2021年10月 2021/10/262021/10/262021/10/2610/26/2021
Unit 7
The sea
Deep sea secrets 你知道海水为什么是咸的吗？它会不会变淡或者变得更咸呢？
Have you ever noticed that，in the summer，when your sweat dries it will leae tiny bits of salt.
If you go to the seaside，you will know that seawater does the same to your clothes，because it also has a lot of salt in it.
Water evaporates ( 蒸 发 ) from the surface of the sea but the salt remains.Have you ever thought about whether the seas will keep getting saltier？ The answer is no.The oceans have stayed at about 3.5 per cent salt content for hundreds of millions of years.It maintains a constant level of salt in different ways.
•7、风声雨声读书声，声声入耳；家事国事天下事，事事关心。2021/10/262021/10/26October 26, 2021 •8、先生不应该专教书，他的责任是教人做人；学生不应该专读书，他的责任是学习人生之道。2021/10/262021/10/262021/10/262021/10/26
Pick up a clamshell (蛤壳) and weigh it in your hand.It is heavy.All creatures need sodium (钠)) to live and most need calcium to build bones and shells.The clam，like all sea creatures，gets its sodium and calcium from seawater.When creatures die，their salt is locked up in bones and shells，which drop to the bottom of the sea.
The outer hard crust of Earth is made up of a dozen or so hard plates that drift (漂流) on extremely hot，soft rock like floating islands on a sea.The heat within Earth is not the same everywhere and the plates move due to the heat.
Reactions between seawater and rocks are not just one way.Sea salt not only dissolves (溶解) from rocks；it also reacts with the rocks of the ocean crust (地 壳) and volcanic lava (熔岩)．The reactions take some of the salts in seawater away from the sea.
So，that’s why the seas are salty but don’t get any saltier.
谢谢观看！
•1、使教育过程成为一种艺术的事业。 •2、教师之为教，不在全盘授予，而在相机诱导。2021/10/262021/10/262021/10/2610/26/2021 7:56:11 PM •3、一年之计，莫如树谷；十年之计，莫如树木；终身之计，莫如树人4、智力教育就是要扩大人的求知范围 •5、教育是一个逐步发现自己无知的过程。 •6、要经常培养开阔的胸襟，要经常培养知识上诚实的习惯，而且要经常学习向自己的思想负责任。2021年10月 2021/10/262021/10/262021/10/2610/26/2021
Unit 7
The sea
Deep sea secrets 你知道海水为什么是咸的吗？它会不会变淡或者变得更咸呢？
Have you ever noticed that，in the summer，when your sweat dries it will leae tiny bits of salt.
If you go to the seaside，you will know that seawater does the same to your clothes，because it also has a lot of salt in it.
Water evaporates ( 蒸 发 ) from the surface of the sea but the salt remains.Have you ever thought about whether the seas will keep getting saltier？ The answer is no.The oceans have stayed at about 3.5 per cent salt content for hundreds of millions of years.It maintains a constant level of salt in different ways.