Things You Thought You Knew – Rocks Float

**Chuck Nice** (0:00)
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**Neil deGrasse Tyson** (1:28)
Hey, StarTalkians. Neil here. I've got another Things You Thought You Knew episode coming right up. This time Chuck and I explain how rocks are light, not heavy, warm blankets and oxygen. Check it out.
Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.

**Chuck Nice** (2:01)
I'm excited to know what we've got going today.

**Neil deGrasse Tyson** (2:03)
We're going to just talk about oxygen.

**Chuck Nice** (2:06)
Oh, man.

**Neil deGrasse Tyson** (2:08)
What's the matter?

**Chuck Nice** (2:10)
Dude, normally, you come to me with some super exciting stuff like, today, we're going to talk about the moon and albedo. Do you know what albedo is? No, man, what is that? That sounds really cool.

**Neil deGrasse Tyson** (2:22)
I'm sorry oxygen doesn't excite you, but maybe by the end of these 10 minutes, it will. That's all I'm saying.

**Chuck Nice** (2:28)
All right.

**Neil deGrasse Tyson** (2:28)
Give it a chance, dude.

**Chuck Nice** (2:30)
Well, listen, I give oxygen a chance every day.

**Neil deGrasse Tyson** (2:35)
Okay. Many people who have never had atmosphere chemistry, they know that we breathe oxygen to survive. We know this, but not everyone knows how much oxygen is in our atmosphere.

**Chuck Nice** (2:50)
Okay. Well, already now I'm interested.

**Neil deGrasse Tyson** (2:52)
Right. So the first guess is, well, it's all oxygen. Of course we're breathing up. That's not the case.
Most of the air we breathe is nitrogen, which has no value in its gaseous form as we inhale it. So we just inhale it and then exhale it.

**Chuck Nice** (3:08)
Okay.

**Neil deGrasse Tyson** (3:09)
Nitrogen is 78% of the air we breathe.
Wow. It's most. Most.

**Chuck Nice** (3:16)
Did not know that.

**Neil deGrasse Tyson** (3:17)
Did not know that. Okay. So now oxygen is between 20 and 21% of the air we breathe. So it's about a fifth of the air we breathe.

**Chuck Nice** (3:26)
Got you. All right.

**Neil deGrasse Tyson** (3:27)
Right. So just let me put that out there, first of all.
Second, as you know, trees and other photosynthesizing life makes oxygen.

**Chuck Nice** (3:38)
Right.

**Neil deGrasse Tyson** (3:39)
One of the delusions of the Star Trek, the early Star Trek series was, they, you ever notice, I've said this in other explainers, they never wear spacesuits when they visit planets.

**Chuck Nice** (3:52)
Every time they come down to a planet, they're just like, well, isn't this nice?

**Neil deGrasse Tyson** (3:58)
No, so they check. It's oxygen-nitrogen atmosphere, Captain.

**Chuck Nice** (4:01)
It's a Class M planet, Captain.

**Neil deGrasse Tyson** (4:02)
Right, so then they go down, it's got oxygen. As though, in the mix of all the planets that are out there, some of them will just happen to have this mix, and so they'll be just fine to be human and then walk down on its surface. Okay?

**Chuck Nice** (4:17)
All right.

**Neil deGrasse Tyson** (4:19)
But if you think it through, the entire source of our oxygen is green plants.
If you take away the green plants, oxygen is highly reactive as a chemical element. And so the oxygen that's in the atmosphere will glom on to other ingredients on Earth's surface, and it will systematically drain out of the Earth's atmosphere, leaving us with none. So if you find a planet that has sustained oxygen, that is evidence of something generating that oxygen, and in our case, it's plants. It could be some other mechanism, none we have ever dreamt of or divined. But if you find a planet with oxygen, it's gonna have plant life.