It's unexplainable, I'm Brian Resnick, and this is the third and last episode of our

origin series.

So far, we've been talking about how life on Earth started, that first somehow came

water.

And then in that water, the right ingredients mixed and form some very basic living thing.

From that point on, life has just been thriving.

You know, there are swoopy fires, microscopic squigglys, giant Earth-shaking elephants.

Life is everywhere.

But it turns out there's a question we've kind of taken for granted.

We've talked about what it might take to make a very basic living cell, but that doesn't

mean we know what life fundamentally is.

No one has been able to define life, and some people will tell you it's not possible

to.

This is science writer Carl Zimmer.

It may simply be that we are trying to put life in a box when it's not the sort of

thing that you can fit into boxes.

This feels like it should be easy.

Like a homework question for a little kid.

Dogs.

Alive.

Creepy crawlies.

Alive.

...