Life probably arose only once on Earth, and the deep split between bacteria and archaea is the evidence for it.

But there’s a very interesting deep split in life between bacteria and what are called archaea, which look just the same as bacteria. And they’re not quite as diverse, but nearly, and they are very different in their biochemistry. And so any explanation for the origin of life has to account, as well, for why they’re so different and yet so similar. And that makes me think that life probably did arise only once.