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What is fire anyway?
火究竟是什么？
Well, fire is rapid oxidization.
火，即燃燒，是快速的氧化反應。
It's the energy released whenoxygen atoms start combining with carbon and hydrogenatoms.
氧化反應是氧原子和碳原子或氫原子結合釋放能量。
Exactly, so without oxygen in the air, nothing burns.
沒錯，那么如果空氣中沒有氧氣，就不會有燃燒。
You mean there was a time before oxygen?
你是說氧氣還不存在的那個時代？
Yes. By roughly a billion years ago, simple forms of plant life called “eukaryotes” were already busilyconverting carbon dioxide into oxygen gas, just like their descendants do today.
對，大約十億年前，和眼下的植物一樣，地球上最原始的植物祖先“真核細胞”忙碌地將二氧化碳轉變成氧氣。
But before thisprocess had been in place for a while, there wasn't enough oxygen in the air for things to burn.
但是，在此轉化之前的一段時間，空氣中沒有足夠的氧氣可以燃燒東西。
In fact, of all the planets, moons, asteroids, and comets in our solar system, the only place whereyou can actually start a fire is right here on earth.
而事實上，整個太陽系的所有的行星、月球、小行星、彗星，你會發現唯一可以生活的地方只有地球。
And even here, it's only been possible relativelyrecently.
而就算是地球，也是不久以前才可行。
