We see this process in action when particles no largerthan grains of sand

我们看到的实景 就是晚上的时候

burn up as they streak across the nightsky.Shooting stars.

有像沙粒一样大的亮光一闪而过 流星雨

One object that didn't burn up was Theia, Earth's twin.

地球早期和自己孪生星球的撞击

Earth's early collision with its twinwas also vital for our planet in many other ways.

在其它方面也很重要

For a start, it probably resulted in Earth's core becoming larger.

一开始，地核变大

And because it's made of iron,

因为它是由铁组成的

the churning of this huge metal core generates a powerful magnetic field.

这个巨大的金属地核就产生了 巨大的磁场

It's possible to see this magnetic field at work.This is the aurora.

我们可以看到磁场如何发挥作用 这是极光

You're watching the magnetic field deflecting

你现在看到的就是地球磁场

the Sun's dangerous solar wind.

将太阳危险的太阳风扭曲

But the huge molten core contributes something else

但是这个巨大的融化内核

essential for life on Earth,

对地球生命还起到其它作用

a way of helping to regulate the planet's temperature.

这是调节地球温度的一种方式

It's a remarkable system.

这是一个很了不起的系统