WEBVTT

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That Earth is nothing remarkable.

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I mean, it's not in a special location.

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It's not the center of the solar system.

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It's not the center of the galaxy.

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The galaxy is not the center of the universe by any stretch.

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And so there's this idea that there's nothing remarkable about the Earth.

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But I don't think that applies when you look at how Earth is capable of supporting life.

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Because what is remarkable about Earth is that it is covered in water.

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But it does not have nearly as much water as you think it ought to.

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And so it looks like there was an event that removed a lot of Earth's water.

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So that it's got enough to cover the surface.

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But it's not so much that land can never peek out above the surface of the waters.

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And in order for there to be land peeking out above the surface of the waters,

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you've got to have plate tectonics.

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Which means the planet has to be about the right size.

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And it probably has to have something like the moon.

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And so now you're starting to throw all of these additional requirements on

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that getting liquid water is actually relatively easy for a rocky planet.

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But having a planet that has enough liquid water that it can sustain it for a long time,

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but not so much that it just completely encases the planet without any hope of continents arising,

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that's a big deal.

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And I would say, you know, even on Earth, what we see is that better,

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almost 70% of life resides either on the continents or in the continental margins.

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And so continents are very important for a planet being able to host a thriving and diverse array of life.

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So to follow up on that, what does that your mind make for it special?

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I think it does imply that Earth is going to be somewhat unique or very rare in its capacity to support life.

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We're going to find lots of planets that orbit in a range where liquid water could exist.

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I would say we don't have the technology to detect whether there's actually water on those planets yet or not.

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But again, water is not the only requirement for life.

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You've got to have water, but you also have to have continents.

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You have to have a stable water cycle.

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You have to have clouds in the atmosphere.

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You have to have plate tectonics.

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When you put all that together, the chances of a planet having all of those things in the way Earth does is pretty remote.

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So, yeah, I think Earth is very special.