【英语时差8,16】为什么磁极会交换方向？（上）

On a previous show we discussed how, every 200,000 years or so, the north and south poles switch places. Not that the places themselves move–rather, the entire magnetic field of the earth flips¹ around, resulting in the pole we now call “north” being on the southern tip of the planet, and vice² versa. Why does this happen? Although it seems pretty solid, the outer core of our planet is in a molten state. That means it’s partway between what most folks would call liquid and solid. Much of this molten interior is iron and nickel. These are elements that conduct electricity very well. It’s the fluid metals that move about inside earth that generate a magnetic field around our entire planet. Although from close up these metals are bubbling like hot soup, you could also say that in general their motions follow a pretty steady pattern. That’s why the magnetic field on earth is pretty stable.

1 flips   

轻弹( flip的第三人称单数 )； 按（开关）； 快速翻转； 急挥

参考例句：

• Larry flips on the TV while he is on vacation in Budapest. 赖瑞在布达佩斯渡假时，打开电视收看节目。
• He flips through a book before making a decision. 他在决定买下一本书前总要先草草翻阅一下。

2 vice   

n.坏事；恶习；[pl.]台钳，老虎钳；adj.副的

参考例句：

• He guarded himself against vice.他避免染上坏习惯。
• They are sunk in the depth of vice.他们堕入了罪恶的深渊。