这是一种闪电
that doesn't strike down towards the ground
它们不直接袭击地表面
but instead reaches upwards within the mesosphere,
而是往上发射，高至中心层
30-50 miles high.
30到50英里高
We've seen the power of the atmosphere to shape the planet
我们看过大气的力量是怎样塑造星球
and create the weather,
和创造气候
but it's the relationship between the atmosphere and life
大气和生命的联系
that has made our planet unique in the solar system.
使我们的地球在太阳系中独一无二
To understand how this vital relationship evolved,
要明白这一重要的关系如何发生
you have to go back to the very beginning of Earth's long history.
得追溯到很久以前地球混沌初开时
The planet's atmosphere was created shortly after the Earth was formed
在地球刚形成不久大气圏就形成了
four and a half billion years ago.
四十六亿年前
The early Earth was probably highly volcanic.
早期地球充满火山
And for millions of years,
几百万年后
these volcanoes spewed out huge quantities of gas.
这些火山喷发出大量气体
Slowly these gases built up and created the atmosphere.
这些气体缓慢聚合创造了大气层
