Things You Thought You Knew – Rocks Float

Summary

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StarTalk Radio: "Things You Thought You Knew – Rocks Float"

Host: Neil deGrasse Tyson
Co-Host: Chuck Nice
Date: June 23, 2026

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Episode Overview

In this lively "Things You Thought You Knew" installment, Neil deGrasse Tyson and comedian Chuck Nice tackle surprising facts and misconceptions about three seemingly mundane topics—oxygen, rocks, and warm blankets. With humor and clarity, they explore scientific insights behind why rocks float (from a planetary perspective!), debunk myths about oxygen’s role in fire, the real reason blankets keep you warm, and draw fascinating links between environmental chemistry, life, and planetary evolution. As always, scientific knowledge collides with pop culture, banter, and comedy for an episode that’ll make you see ordinary things in an extraordinary new light.

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Key Discussion Points & Insights

1. Oxygen: More Than Just Air We Breathe

Timestamps: 01:17 – 21:20

• Atmospheric Composition

  • Most people mistakenly believe our air is mostly oxygen, but nitrogen makes up 78%. Oxygen is only about 20-21% ([02:18]).
  • “Most of the air we breathe is nitrogen.” – Neil ([02:15])

• Oxygen’s Origin and the Star Trek Problem

  • On "Star Trek," planets with breathable air are depicted as an interplanetary lottery—where “class M” planets conveniently have just the right mix ([03:19]).

  • Tyson points out: sustained atmospheric oxygen requires active generation—on Earth, it's green plants and photosynthetic organisms. Without them, oxygen would react and vanish from the air ([03:37]).

    • “If you find a planet with oxygen, it’s going to have plant life—or something like it—generating oxygen in real time.” – Neil ([04:18])

• Oxygen and Combustion: Myths vs Reality

  • Oxygen is NOT flammable itself—rather, it promotes combustion. It makes burnable things burn faster, but does not ignite ([08:08]).
  • Apollo 1 Tragedy
    • The Apollo 1 disaster: a pure oxygen environment led to a deadly fire; the culprit wasn't burning oxygen but accelerated burning of everything else ([09:50]).
    • “The oxygen enabled everything burnable to burn—to continue to burn. The astronauts themselves.” – Neil ([10:43])

• Movie Science: “Jaws” and the Oxygen Tank

  • In "Jaws," shooting an oxygen tank to blow up a shark is Hollywood fiction. Oxygen tanks explode not because of oxygen but because of compressed gas under pressure ([12:02]).

• Oxygen Levels and Biosphere Consequences

  • If oxygen levels were higher (e.g., 30-50%), forest fires would never end ([15:21]).

  • Insect size is limited by oxygen content—higher oxygen in the dinosaur era allowed for giant bugs ([16:35]).

    • “If you have more oxygen in your air, this is like rocket fuel for [insects]—and they can grow bigger.” – Neil ([16:35])

• Cyanobacteria: Earth’s Great Terraformers

  • Cyanobacteria radically changed the Earth’s atmosphere billions of years ago, raising oxygen and causing mass extinctions of oxygen-sensitive organisms—but enabling complex animal life to arise ([17:22]).

    • “The only species ever to change the ecosystem of the Earth? Cyanobacteria.” – Neil ([17:22])

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2. Rocks Are Light (…Sort Of)

Timestamps: 22:26 – 31:09

• What Does It Mean for Rocks to Be ‘Light’?

  • Tyson redefines “light” in terms of density, not weight. Rocks are denser than water or air, but on a planetary scale, they’re the “light stuff” that floated to Earth’s surface when it was molten—denser materials (metals) sank to the core ([24:49]).

    • "Earth’s crust, where the active ingredient is rock, is the lightest stuff in Earth when it formed." – Neil ([25:57])

• Planetary Differentiation: Why Iron Is Deep and Rocks Are Shallow

  • The densest elements (iron, nickel) reside in the core, followed by lighter materials (rock), with air and water sitting above ([26:22]).
  • Humans, and even battleships, can float in water. Ships float thanks to their average density (mostly air).

• Finding Meteorites – Why Antarctica Wins

  • Most meteorites are rocky and blend in on a rocky planet. Meteorite hunting is easiest in Antarctica and deserts, where rocks stand out ([30:14]).
    • “Because every other place on Earth is made of freaking rocks.” – Neil ([30:19])

• Pumice: The Floating Rock

  • Pumice is even lighter—it floats because it’s filled with air pockets ([30:46]).
    • “Pumice is even lighter because it’s got air in it.” – Neil ([30:46])

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3. The Science of Warm Blankets

Timestamps: 33:59 – 45:50

• Blankets Don’t Generate Warmth

  • Blankets aren’t inherently warm; they don’t make things warmer. They work by slowing heat transfer—insulation ([35:31]).
    • “If the blanket were actually a source of warmth, you could put it over the tile, wait a while, peel back the blanket, and then the tile would be warmer than the surrounding tiles.” – Neil ([36:02])

• Why We Feel “Warm” Under a Blanket

  • We lose heat to our surroundings; a blanket prevents loss, trapping what our bodies produce ([37:01]).
    • “What we really mean when we say a garment is warm is that it does not transmit heat energy.” – Neil ([37:01])

• Blankets Keep Cold Beer Cold, Too

  • The same insulation can preserve cold as well as heat (like a thermos)—showing “warm” is just a point of view ([39:41]).

• Mittens vs. Gloves: A Physics Lesson

  • Mittens keep fingers more insulated (sharing heat), while gloves separate them, making individual digits colder ([42:06]).

    • "In a mitten, when one finger loses heat, it goes to the next finger … you're radiating to yourself inside the mitten." – Neil ([42:14])

  • Chuck delivers an impromptu metaphor for American society:

    • “America, the country that prides itself on being a glove, where each finger is independent... when right now, what we really need to be is a mitten. Each one of us giving heat to one another, relying upon each other in order to be warm together.” – Chuck ([43:12])

• Physical Limits & Relationships

  • Only one person can feel warm at a time when snuggling—someone must be losing heat ([44:17]).
    • “Two people cannot feel warm with each other at the same time.—Thermodynamically, that’s not possible.” – Neil ([44:50])

• Insulation for Reptiles

  • Blankets don’t help cold-blooded animals much—they equilibrate to the environment, unlike mammals ([45:13]).

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Notable Quotes & Memorable Moments

• “If you find a planet with oxygen, it’s going to have plant life.” — Neil ([04:18])
• “Oxygen promotes combustion. That’s why they have those labels there.” — Neil ([06:16])
• “So in a way it’s self-correcting. Too much plant life creates too much oxygen. So the next lightning strike will take it out, preventing more oxygen from coming in.” — Neil ([15:32])
• “Pumice is even lighter because it’s got air in it.” — Neil ([30:46])
• “So think of it not as a warm blanket, just as a blanket serving as a thermos in your life—to keep the cold beer cold or you warm at your body temperature.” — Neil ([45:13])
• “If you are using a blanket to keep your beer warm, I invite you to a little place called Walmart or Target to buy a cooler.” — Chuck ([47:10])

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Timestamps for Key Segments

| Segment | Description | Start | |-----------------------------|-------------------------------------------------------------------------|---------| | Oxygen & Air Composition | What’s in our atmosphere, how oxygen gets there, its chemical reactivity | 01:17 | | Star Trek & Alien Planets | Why oxygen-rich planets indicate life | 03:08 | | Oxygen and Fire | Is oxygen flammable? Apollo 1 tragedy, fiction vs. reality | 06:48 | | Oxygen in Pop Culture | "Jaws" oxygen tank, movie myths | 11:42 | | Oxygen & Ecosystem Balance | Why life and atmosphere co-evolve, cyanobacteria impact | 15:21 | | Rocks are “Light” | Planetary differentiation, density, meteorites, pumice | 22:26 | | Warm Blankets Explained | Insulation, heat transfer, thermos analogy | 33:59 | | Mittens, Gloves & Metaphor | Why mittens are warmer, and a metaphor for society | 42:06 | | Relationships & Blankets | Why only one person feels ‘warm,’ reptile insulation | 44:50 |

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Episode Tone

Playful, sharp, and filled with witty asides. Neil brings scientific rigor merged with geeky pop culture references, while Chuck delivers comic relief and insightful questions. The episode is fast-paced but clear, breaking down complex topics for a general audience without losing the science.

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Summary Takeaways

• Oxygen: It’s reactive, promotes combustion (not flammable), and is a sure sign of planetary life if detected elsewhere.
• Rocks: Despite seeming heavy, rocks “float” on a planetary scale—so what’s beneath us is denser, and Earth is differentiated by density.
• Blankets: There’s no such thing as a "warm blanket"—it’s all about slowing heat transfer, making thermodynamics as cozy as it gets.

Chuck’s final comic moral: If you’re using a blanket to keep your beer warm, go buy a cooler!
Neil’s closing: “Keep looking up.”

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Transcript

[A]

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[B]

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.

[C]

I'm excited to know what we've got going today.

[B]

We're gonna just talk about oxygen.

[C]

Oh, man.

[B]

What's the matter, dude?

[C]

Normally you come to me with some, like, super exciting stuff, like, you know, today we're gonna talk about the moon and albedo. Do you know what albedo is? No, man. What is that?

[B]

That sounds really cool. 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.

[C]

All right?

[B]

Give it a chance.

[C]

Give it a. Well, listen, I give oxygen a chance every day, okay?

[B]

Okay. Many people who have never had atmospheric chemistry, right, they know that we breathe oxygen for to survive. We know this, right? But not everyone knows how much oxygen is in our atmosphere.

[C]

Okay, well, already now I'm interested.

[B]

Right? So the first guess is. Well, it's all oxygen, right? Of course we're breathing. That's not the case.

[C]

Right.

[B]

Most of the air we breathe is nitrogen.

[C]

Nitrogen, okay.

[B]

Which has no value in its gaseous form as we inhale it. So we just inhale it and then exhale it.

[C]

Okay.

[B]

Nitrogen is 78% of the air we breathe.

[C]

Wow.

[B]

It's most. Most.

[C]

Did not know that.

[B]

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.

[C]

Gotcha.

[B]

All right. Right. So just let me put that out there. First of all, Second, as you know, trees and other photosynthesizing life makes oxygen.

[C]

Right.

[B]

One of the delusions of the early Star Trek series was, you ever notice I've said this in other explainers, they never wear spacesuits when they visit planets.

[C]

Every time they come down to a planet, they're just like, well, isn't this nice?

[B]

No. So they check it's oxygen, nitrogen, atmosphere,

[C]

it's a class M planet.

[B]

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 it'll be just fine to be human and then walk down on its surface. Okay. All right. 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, right. That is evidence of something generating that oxygen, and in our case, it's plants. That could be some other mechanism. None we have ever dreamt of or divined. But if you find a planet with oxygen, it's going to have plant life.

[C]

Wow. Right.

[B]

Or something that is generating oxygen in real time. And in the planets they went to, that was never discussed because I think they just believed in the planet lottery. Some planets have oxygen and others don't.

[C]

And you know what's funny that you say that many of the planets that they beamed down to were very Mars, like, so they're very rocky rock. There's no vegetation at all.

[B]

I think the rocks are easier for the propped people to make than whole trees with plumage. Right. Yeah. It was very barren. Correct. You remembered this. So that's one little thing about the oxygen I put out there. Okay. Also, by the way, on the planets they landed on, they were never sort of bounding the way the astronauts did on the Moon. Those planets all had about 1G, just like Earth.

[C]

Yes.

[B]

And the atmospheric pressure was about that

[C]

of Earth, the same as Earth.

[B]

There are some planets that are the same size as Earth and the same gravity as Earth, but the atmospheric pressure is 100 times that of Earth. So they'd beam down and just get flattened.

[C]

Flattened like a. Like they got hit with a fly swatter?

[B]

Yeah, basically.

[C]

Wow.

[B]

Yeah. Okay, so more about oxygen. There's this belief that oxygen is flammable.

[C]

Okay. Maybe that's not. Because every oxygen tank I've ever seen has the word flammable written all over it. That might be why people believe. Believe that you go to any hospital, you going see a tank. You going to see a tank in a corner, and on that tank is going to be a little fire emoji with the word flammable.

[B]

Is that what's on tanks? Emojis?

[C]

I didn't know that. Okay,

[B]

all right, so I should clarify what's going on there. Okay. Okay. Oxygen promotes combustion. That's why they have those labels there. So if you. This won't happen today, ever. But in the day. You walk into a hospital smoking a cigarette. Okay. If you go into a hospital room.

[C]

Wait a minute. Now I'm just seeing a doctor. Smoke. Smoke. Smoking a cigarette. Scalpel. With a hole through the mask. Scalpel. Scalpel.

[B]

Wait, let me cauterize this.

[C]

Exactly.

[B]

Hold on.

[C]

Ah, there we go. Oh, Jesus. I think I dropped my butt in this guy's open abdomen. Anybody seen a cigarette butt?

[B]

And you got this smoker's voice too.

[C]

Exactly. Oh, my God. Your doctor sounds like a diner waitress. Well, listen, dear, I don't want to give you bad news, but here's the low. Here's the lowdown. Hon, let me get you a coffee and then we'll talk about this. Pork.

[B]

The smoking New York Diner.

[C]

Diner doctor. Oh, man. Okay.

[B]

All right, so here's what happened. It promotes compliance. So if you're in a room of oxygen and you bring in a lit cigarette, the cigarette would instantly go up in smoke.

[C]

Wow.

[B]

Instantly. I mean, it would go from the lit spot, but it would go. And the whole thing would just ignite instantly.

[C]

Gotcha.

[B]

But you're not going to ignite the gas in the room. That's my point. Aha. The oxygen itself does not burn, so.

[C]

Oxygen. Cause. No, I was about to say it's like a non burning accelerant.

[B]

Okay, I can. Yes, sure.

[C]

I mean, that's. I'm trying to make sense of this because it's.

[B]

I'll allow that, but I think in firefighter talk, accelerant. Accelerant burns might mean something else. Right. So this is what happened. Apollo 1.

[C]

Uh.

[B]

Oh, Apollo 1. All right. Nobody's ever heard of Apollo 1 because it never went anywhere. It was that through Apollo 6, I think it was, was a set of designs of the capsule that would take three astronauts to the moon. There they are on the launch pad, testing on a testing pad. And in the capsule is pure oxygen.

[C]

Whoa.

[B]

Here's why. Because if they had an oxygen nitrogen mix, you would have to pressurize the inside to equal atmospheric pressure so that you'd have the right amount of oxygen that you're accustomed to breathing. If you do that, you have to over build the strength of the capsule to contain one atmospheric pressure against the vacuum of space.

[C]

Gotcha.

[B]

So all the joints, the bolts and the hinges and the door closures and the window would have to be extra strong. So they said, why burden ourselves with this? Let's instead put in pure oxygen. Then we don't need to have to have it at full pressure.

[C]

That's actually kind of brilliant. It's brilliant.

[B]

It's brilliant. Now we could be much lower pressure, but it's all oxygen. So now you take in a breath, it's less total air, but it's the right amount of oxygen that your body's expecting. Okay. All right. In that capsule, there was an electrical fire. Oh, there was a spark that immediately burned all of the insulation, the thing, their suits. And they could not open the hatch in time. All three astronauts were burned to death.

[C]

Oh, gosh.

[B]

Yep.

[C]

That is just awful.

[B]

Yeah, it's terrible. It's so again, it's accidents like that where we think the oxygen was burning, but that's not what was burning. The oxygen enabled everything burnable to burn to continue to burn. The astronauts themselves. Correct. We lost three astronauts in that fight.

[C]

Damn. That is. Oh, my God. That's just terrible.

[B]

Right, right.

[C]

So now what's it take, two to listen? Cause let me just tell you, let me just say this. First of all, it's a tragedy. And I would dare never infringe upon the sanctity of those men and lives. But I will say this. If I'm the next three astronauts, I just quit the space program.

[B]

No, no, here's what they did. Instead of saying, okay, let's try Apollo 2. Okay. No, what they did was they scrapped six Apollo designs and came up with Apoll 7. I think it was seven or eight. No, Apollo 7. And so they were nowhere near what that design was by the time they had the next vessel in place.

[C]

Okay, all right.

[B]

That would have satisfied you, I think.

[C]

Yeah.

[B]

So anyway, so that's another thing with oxygen. Here's another one. You ready? In the movie Jaws, okay. There's a tank of oxygen.

[C]

Yes.

[B]

On deck at the end.

[C]

Right.

[B]

And the captain, I think Richard Dreyfuss character bumps into it. He says, watch out, that's oxygen.

[C]

Okay.

[B]

All that mattered for the movie was that what was in the tank was compressed gas.

[C]

Right.

[B]

But they're saying, watch out, it's oxygen, right? Oxygen. So what happens? How do they finally defeat the great white shark? Okay, I forgot which. It's been a while since I've seen the film. One of them, I think, while the shark is munching on the boat, takes that oxygen tank and shoves it into the mouth of the shark, right? Then dives off the boat. I'm making some of this up because I don't remember the details, but the shark, you can see the tank in the shark's mouth. The guy takes his high powered rifle, shoots the tank and the tank explodes, blowing the head of the shark off. And then peace reigns in Nantucket or wherever the hell this was.

[C]

Yep.

[B]

Okay, so what mattered there was not that it was oxygen, but that it was gas under pressure. And when you punched a bullet hole in it, probably it just would have been a hole and would have gone.

[C]

I was gonna say the shark should have just shot off into the distance.

[B]

Yeah, he would have had a little

[C]

retro rocket, little rocket mouth. Shark has rocket mouth now and it's just like.

[B]

So that's probably what would have happened. But if this tank is not structurally sound and it can't accommodate a hole, it could conceivably blow up. But it blew up not because it had oxygen in it, right? Because it was gas under pressure. So that's different from if you leave your gas and your stove on and all your windows are closed and you go out and you come back now there's gas everywhere in the house. A spark, right, Won't just burn. What sparked all the gas will now ignite and explode. And that's the difference between methane gas, which is flammable, and oxygen gas, which is not.

[C]

Right, Right. And the other difference is normally that's kind of like insurance fraud.

[B]

Oh, yes, yes. Okay. In the old days, I don't know if there's as much of that today.

[C]

Yeah, they got too much forensic science.

[B]

Too much science.

[C]

They got too much science. It's your people.

[B]

Your people screwed it up. We can science the shit out of whatever you just did. Right?

[C]

I can't collect the insurance on my failing business now, thanks to you guys ass in jail.

[B]

So a couple more things. Okay. As you may know, plant life likes carbon dioxide. Of course it absorbs it. Okay. And that carbon becomes part of the fibers of the wood and out comes oxygen, which we breathe. Okay, if you have too much plant life and it creates, let's call it excess oxygen. Okay, let's say 30% oxygen in the atmosphere, and there Are calculations that do this, which I can't quote precisely, but just some number above the 21% that we now have. Take it to 30, 40, 50% oxygen. Imagine a world where plants are just pumping this out and they're loving it. Okay. In that world, forest fires never end.

[C]

Oh, that makes sense. Because they're being fed by oxygen all the time.

[B]

By oxygen. Correct. So there's a fuel of the wood

[C]

and then the oxygen is also fueling it too.

[B]

So in a way it's self correcting. Too much plant life creates too much oxygen. So the next lightning strike will take it out, preventing more oxygen from coming in.

[C]

Oh, wow. It's its own check and balance.

[B]

Correct, Correct. So it's just interesting to think about how you end up pegging oxygen at one level versus another.

[C]

Interesting.

[B]

One other thing, and I think we talked about it in our surface area explainer. Insects don't, most of them don't have lungs the way we think of. We breathe in and we have lungs and that's how we get our oxygen. Insects, many of them rely on absorbing oxygen through their surface area. Right, okay.

[C]

Which is why they never need breath mints. But.

[B]

Yeah, that's right. Is that right? Thank you for telling me. Okay, so they. And so if you have more oxygen in your air, this is like rocket fuel for them.

[C]

Wow.

[B]

And they can grow bigger.

[C]

Hello.

[B]

Because when you're bigger, your surface area to volume is lower. But if you have. We did that in an explainer. You have to dig that one up. If you're bigger, you have more volume to your surface area. So now you're not gonna get enough oxygen to feed your fat body. But if the oxygen levels are higher, you can. And so that's why you had those huge dragonflies back at the time of the dinosaurs.

[C]

Right.

[B]

Okay. Oxygen levels were higher back then. You had these huge insects. So oxygen levels have consequences in the biota of Earth. Nice.

[C]

Wow. So who knew that all of this, who knew all this about O2?

[B]

Exactly, exactly. And oxygen wants to combine and so it combines with itself best. So you have an O2.2 oxygen. And one last thing, people talk about humans wrecking the earth. You know, the only species ever to change the ecosystem of the Earth. That is just false. The creature that had the greatest effect on the climate and conditions of the earth were the cyanobacteria of when it was this, three and a half billion years ago. Something like that. At that time, Earth's atmosphere was mostly carbon dioxide. Hardly any oxygen at all. They take in carbon dioxide and spew out oxygen.

[C]

Wow.

[B]

And they built the oxygen supply of our atmosphere to levels that were caustic to animals that don't like oxygen.

[C]

Right.

[B]

So this killed off entire branches of the tree of life who were doing just fine in their carbon dioxide atmosphere, but it enabled other forms of life to rise up that would exploit the oxygen for their own benefit.

[C]

Wow. Wow. So why can't we just use cyanobacteria as a carbon scrubber for our current situation where we have to mitigate the amount of carbon in the atmosphere?

[B]

Yeah, that's a good. Okay. So sure, you have to watch out for unintended consequences.

[C]

Right. Cause guess what? We already saw one unintended consequence of cyanobacteria. Thanks. Cyanobacteria.

[B]

You know, I mean, it's. Who knows? We should probably get people to look into that to have biological CO2 scrubbers, which is what plants are.

[C]

Right.

[B]

But again, they're putting more oxygen in the air, and that also has consequences. So. Yeah.

[C]

Wow, that was great. Anyhow.

[B]

You got it, dude.

[C]

I started off saying oxygen was boring, but, you know, I was raw.

[B]

Yeah. And by the way, if oxygen were actually flammable, every time you lit a match, it would just burn. Your air would burn out.

[C]

That would be actually. That'd be kind of cool.

[B]

Or you could just pump oxygen through your. Through the gas. Right, Your gas stove. But no, we don't, because it's not flammable. That's all I gotta tell you about oxygen. Do we have any good reason to think that aliens would be evil? Where did we get that idea from? Aliens could be the most peace loving creatures the universe has ever generated, yet our representations of them tend to be diabolical. Which gets me to wonder that these representations of evil aliens are not based on how we think they will behave. That maybe they're really based on how we know we have behaved to one another. Especially when there's a conflict between a higher technology and a lower technology. So exploring the topic of aliens can not only give us insights into all the ways of being alive in the universe, it can, on occasion, hold up a mirror to our greatest fear, which might, in fact, be ourselves. That and more in my latest offering, Take Me to youo Perspectives on youn First Alien Encounter. I narrated the audiobook that's available with the print version, and I'm kind of thinking you should get it now. It'd be too late. If you have your first alien encounter and have not yet read the book, you want to be ready. Suffering from dry, tired Irritated eyes Don't

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[B]

I sold my car in Carvana last night.

[A]

Well, that's cool.

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No, you don't understand. It went perfectly. Real offer down to the penny. They're picking it up tomorrow. Nothing went wrong.

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That is the problem. Nothing in my life goes as smoothly. I'm waiting for the catch.

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Maybe there's no catch.

[B]

That's exactly what a catch would want me to think.

[C]

Wow.

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You need to relax.

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I need a knock on wood.

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Do we have wood?

[B]

Is this table wood?

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I think it's laminate.

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Okay. Yeah, that's good.

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I got one for you.

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Ready? Go ahead.

[B]

That rocks are light.

[C]

You mean pebbles.

[B]

No, rocks as in rocks. Little teenies, boulders. I don't care. I don't care what size. I don't care. They're all light. What I mean by light is that they're low density. Now you might say. No, they're not.

[C]

Yeah, I was going to say.

[B]

Okay, Hercules

[C]

rocks are so damn light.

[B]

Boulders like. Well, we went over weight and density on another explainer.

[C]

Yes, we did.

[B]

We could say, a big tree is heavy, but it floats. Okay, so how heavy could it be if it floats?

[C]

But a battleship floats too.

[B]

A battleship floats. So the average density of a battleship or even an aircraft carrier is less than water. Because when you do a cross section through an aircraft carrier, it's mostly air.

[C]

Okay.

[B]

Okay. Most of a ship is ever air. And so that's why. Great discovery, by the way. To realize you can make a boat out of something that itself. The material doesn't float.

[C]

Float. Right.

[B]

You have to. It's the design of the hull that

[C]

I guarantee you that guy was not well received.

[B]

No, what he did was it transformed naval warfare. You didn't have to make a ship out of wood anymore. You can make it out of steel. Just put enough hull in there and you're good. So.

[C]

God, that would have been cool to be on the first steel battleship going up against wooden dudes.

[B]

Yeah. You would just plow through that's called asymmetric advantage in warfare.

[C]

Nice.

[B]

Okay, I like that. Yeah. So the first person with a gun when all you have is a bow and arrow. Asymmetric advantage. Okay? That's how it works.

[C]

Also called winner.

[B]

Winner. You won that battle.

[C]

Okay.

[B]

If you knew there was a bow and arrow and somebody's shooting you down, you say, okay, we're good. We good. That's like aliens with ray guns and you're up there with a pistol shooting at it. It's like, no. Can you just see the situation here?

[C]

I am so glad you said that, because I hate when they do that. Where?

[B]

In the movies.

[C]

When the movies, when the earthlings go up against the aliens and the earthlings are shooting bullets and the aliens are shooting, like, laser beams.

[B]

Laser beams that vaporize their homes.

[C]

Right. And I'm like, really? Come on. And we win.

[B]

Come on.

[C]

Come on. All right. But. But a pistol to a laser fight. Get out.

[B]

All right, back to rocks.

[C]

Rocks are dense or not dense.

[B]

No, they're light. They're light. Now, here's why Earth was once molten. Okay. When? In the early days of formation, Right. When you're molten and you're as big as the Earth, Right. Gravity will do things to that molten mixture. Okay, Right. That makes sense. Right? So if you're denser, if you're heavier, if you're denser, you will sink to the middle.

[C]

Right, that makes sense.

[B]

If you're lighter, you'll float. This happens with any. If you're mixing oil and vinegar for your salad, okay. You're mixing anything. Layered cocktails, for example. And generally, well, always the lower density stuff will float on top of the higher density stuff. Some things you can mix and it'll stay mixed for a while. That's cool. But that's how things work. Okay, so why is it that when you walk around Earth's surface, you find rocks? Okay, Earth does not have rocks in its core. You know what it has in its core? Iron, Iron, nickel, magnesium.

[C]

Right.

[B]

Okay. It's got heavy metals in its core because all the heavy stuff sank to the middle and all the light stuff floated to the top. So Earth's crust, where the active ingredient is rock, is the lightest stuff in Earth when it formed.

[C]

So the. Oh, my gosh.

[B]

Sorry, sorry, sorry. It's the third lightest. It's the third lightest.

[C]

Third lightest.

[B]

The very lightest stuff are the gases. Okay.

[C]

Okay. Yeah.

[B]

So they're floating over your head.

[C]

Right.

[B]

Okay. And next is the water.

[C]

Okay. All right.

[B]

Okay. So the water sank to the bottom of the gas makes sense. Okay. That's Earth's surface.

[C]

All right.

[B]

And what sinks to the bottom of the water?

[C]

Rocks.

[B]

Rocks. And what sinks below the rocks? All the rest of the crap that earth is made of that's heavier than the rocks.

[C]

So rocks are the third lightest thing that came about in the creation of the Earth?

[B]

Yes, basically. Basically. And it's made our crust now. Everything didn't solidify in the same instant.

[C]

Okay. So.

[B]

And plus, you have volcanoes that communicate lower layers with upper layers and things. So there is some of this. But that's why if you're looking for iron, you gotta find the iron ore.

[C]

Okay, the iron ore. What?

[B]

You know, exactly.

[C]

I'm sorry. I had to do it. I had to do was so bad, but I couldn't.

[B]

It was bad. It was so bad. It was.

[C]

I know.

[B]

It was so bad. It was good. Okay, so there's iron ore, nickel ore. So it's not everywhere. There are these places where these veins had been preserved at the point Earth was solidifying. Okay. So you get this. Remnants of this stuff. You want to find out where most of the iron is. And most of the nickel is on Earth. It is in the center of the Earth. And the universe has a lot of nickel and iron in it. So Earth got plenty of its share of those two ingredients, and it's in our core. And you might say, well, how you know you've never been there. Let me hear it.

[C]

Well, how do you know you've never been there?

[B]

I like that accent. You bought that? That was the obnoxious in the classroom.

[C]

How do you know, Mr. Astrophysicist? You've never been there.

[B]

So we have geophysicists who, anytime there's an earthquake, right. They can time the passage of the. Of the earthquake signals through the different layers of the earth. And depending on where and when they receive them at other stations, they can map the density profile of the entire Earth. Holy crap. Because the wave moves through dense materials differently. Differently from light materials. And once you know that, you can figure that out, and bada bing, we've got an iron core.

[C]

That's amazing.

[B]

There you have it. So we think we're about the density of water, all right. Approximately. Some people float, some people sink. That humans are about the density of water. So we think of rocks as heavy and relative to us, they're heavy and relative to water, they're heavy relative to air, but not relative to the rest of the Earth. That's why you don't have to have a mining operation to find rocks,

[C]

they're sticking out of the side of mountain. They have floated to the top of the mountain.

[B]

Floated to the top. And they're there for the taking.

[C]

That's so cool.

[B]

And by the way, that's why it's so hard to find meteorites on Earth's surface. Because most meteorites are rocky and so it'll land and it just looks like any other rock. So you gotta go to places where they would stand out. And there are two kinds of places where that happens. One is the desert. Sandy desert, sand and rock. One problem is that sand will cover it over. Often, however, sand will also blow away. And if you see a rock sitting in the middle. Cause you can scan like many square miles at a pop. Okay. So you say, oh, there's something sticking out of the sand over there that just got revealed. Go over it. It's probably a meteorite.

[C]

Wow.

[B]

Okay. A B. Another place you can go is glacier ice sheets in Antarctica and in Greenland. So most meteorites in the. In our collections, in our modern collections come from Greenland and Antarctica for just that reason. Because every other place on Earth is made of freaking rocks.

[C]

Right? So there's probably tons of them there, but they're just hanging out with other rocks.

[B]

Because some people ask, how come all the meteorites are aiming for Antarctica?

[C]

Right.

[B]

Or that's like the thing. How come I only find my car keys near the lamppost?

[C]

Right.

[B]

At night? Right. Well, because that's the only place you would have seen them.

[C]

Right.

[B]

Okay. But we're good.

[C]

Wow, that was cool, man. Rocks are light.

[B]

Rocks are light.

[C]

Rocks are light, people.

[B]

And pumice is even lighter because it's got air in it. Air is helping it out. Yeah, that's the. That's the fast solidifying rock from a volcano when it hits the ocean.

[C]

It's also great for taking dead skin off your feet.

[B]

But no, I don't want.

[C]

That's.

[B]

Yes, that's why God put pumice on this world.

[C]

Exactly, man.

[A]

That's.

[C]

So that's the best use of it.

[B]

Never mind that God could have made it so that you never got rough feet in the first place. Okay, I didn't perfect that foot thing. Let me give you something else to help that. Okay. That's the second round of creation, Right?

[C]

Okay. Yes, exactly. The first round was the actual body and the second round was cosmetics

[B]

for those days where even God couldn't help you.

[C]

Right. That's. Yeah, it's like I can't even do anything with this. Yeah.

[B]

Take some pumas.

[C]

Yeah. Take some of this other stuff, right?

[B]

You do need l' Oreal.

[C]

Baby. I can't help. You need Max Factor. I cannot help you.

[B]

You need oil of old age. You.

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[B]

Hey, sweetie. Your mother showed me this Carvana thing for selling the car. I'm going to give it a try. Wish me luck.

[A]

Me again.

[B]

I put in the license plate. It gave me an offer. Unbelievable. Okay, I accepted the offer. They're picking it up Tuesday from the driveway. I haven't even left my chair.

[C]

It's done.

[B]

The car is gone. I'm holding a check anyway. Carvana, give it a whirl. Love ya.

[A]

So good. You'll want to leave a voicemail about it. Sell your car today on Carvana. Pick up fees may apply.

[B]

I'm Brian Futterman and I support StarTalk on Patreon.

[C]

This is StarTalk with Neil DeGrasse Tyson.

[B]

I got a topic for you.

[C]

Okay.

[B]

Warm blankets.

[C]

All right. What is happening to us? What is going on that warm blankets are.

[B]

It's a topic.

[C]

What's the next. What's the next explainer going to be? Snuggling. Okay.

[B]

Just saying there's physics everywhere and I just want to sort of bring warm blankets. That time has arrived to come to understand warm blankets.

[C]

First of all, warm blankets sounds like a new emo band. And secondly, I am.

[B]

It's an underused title for something out there.

[C]

It is. Yeah. Warm blankets. But I will say that I'm excited to see the Physics in warm blankets.

[B]

Okay, so here you go. You ready?

[C]

Okay, here we go.

[B]

Okay, here we go. When you look at a coat or a blanket or an item of clothing. So that's a warm item of clothing.

[C]

Right.

[B]

Obviously, when it's sitting on the hanger, the temperature of the clothing is the same as the temperature of the air. Okay? Okay. So you don't say, oh, that's a. If. If there's a blanket sitting on the tile floor, you don't say, oh, that's a warm tile. You say, oh, that's a warm blanket. But they're the same temperature. Right. If they're just sitting out there in the air, they'll be the same temperature as each other. So why are we thinking the blanket is warm, but the tile is cold when they are the same temperature?

[C]

Interesting. And the funny thing is, we do make that distinction because you will look at the blanket and call it warm and call the tile cold or cool, even though. Even though they're sitting there together.

[B]

They're sitting there together at the same temperature. Okay, so here's the thing. If the blanket were actually a source of warmth, you could put it over the tile, wait a while, peel back the blanket, and then the tile would be warmer than the surrounding tiles.

[C]

Now I just picture tile on the floor just going, oh, man, snuggly tiles. Oh, that was so good.

[B]

I'm tired of people calling me cold do that.

[C]

Why does it put the blanket back? So

[B]

the point is, the blanket doesn't make anything warm. It is completely passive in this. It's not a source of warmth. If it were, you could put it on something cold to warm it up.

[C]

True.

[B]

That's all I'm saying.

[C]

It is not a source.

[B]

It is not a source. Even though our language calls it a warm blanket or warm mittens or warm anything else. Okay, so what we really mean when we say a garment is warm is that it does not transmit heat energy.

[C]

Right.

[B]

That's all we mean. Even though that's not what we're saying.

[C]

Okay, first of all, that doesn't sound very comfortable. I just want to get under a blanket that doesn't transmit heat energy. Sweetie.

[B]

New catchy ad for the blanket commercial.

[C]

Right? Come on under here, and let's get under this thing that doesn't transmit heat energy.

[B]

So here's the point. If you put the blanket on the tile, there is no heat difference between them. So nothing is happening. There's no. Okay, so now watch. Now I put it on you,

[C]

so

[B]

you are warmer than the blanket if you Got the blanket out of the closet or on the shelf. Okay.

[C]

Right.

[B]

The blanket is just room temperature. You are warmer than the room, than the blanket, and right now you are radiating heat to the air.

[C]

Yes, I am losing heat because I am hot.

[B]

Baby, you are radiant.

[C]

I am hot coming in hot. That's what I am.

[B]

So you come on in, and so you feel cold because you're losing heat to the air. Okay. And then you say, oh, there's a warm blanket. Let me go get it. So now you bring the blanket. And now the blanket doesn't let you lose the heat to the air. You keep that heat and you interpret what's going on as the blanket being warm when all that's happening is that you are no longer losing the heat you were a minute before you put on the blanket. Now, you might say that's just semantic. No. Okay. Because let's say you brought in some cold beer.

[C]

Okay?

[B]

You don't have any ice yet, but you got it out of the refrigerator cabinet. It's cold beer. It's sitting on the floor. And you say, I don't want the beer to warm up. Let's get a warm blanket to put on it.

[C]

Okay.

[B]

Okay. Because how does the beer get warm? It's taking heat from the air. Okay. Because the air is warmer than the beer. So what you need is super blanket that does not transmit heat energy across its thickness. So you take a blanket, put it on the beer. It'll keep the beer cold by preventing heat from coming from outside of the beer, from entering the beer.

[C]

Oh, man. So.

[B]

So the point is. So the blanket that you're calling a warm blanket is also a cold blanket.

[C]

It's a cold blanket, too.

[B]

Now, and by the way, we have another word for things like that that you carry around, and it's called the thermos.

[C]

Okay, that's true, right? Yes. Whether it's a thermos cooler or a thermos for liquids, it's.

[B]

The thermos keeps hot things hot and cold things cold.

[C]

Right.

[B]

The thermos is the ideal blanket for the food that's contained within it. So if you wanted the best bed of them all, turn it into a thermos. It's just not cuddly, but, boy, you will stay you. In fact, you'll become too hot because your body needs to actually cool off, otherwise you'll overheat. So I just wanted to clarify the fact that warm blankets are simply blankets that don't transmit heat energy. And it'll work keeping your beer cold or you warm and more broadly, it'll maintain the temperature of whatever it is it's covering.

[C]

There it is. And if you're not having a good time, then that's a wet blanket. But that's a whole other explainer. Whole nother explainer.

[B]

That's another whole nother.

[C]

Another.

[B]

So basically, this is what insulation is. Insulation. We don't think of blankets as insulation, but that's what they are. And if one blanket is not working for you, you get a second blanket. So the two combined make it even harder for heat to transfer from one place to another.

[C]

Okay, so now how does that. How does that explain why no matter how many blankets I put on my wife, her feet are still cold?

[B]

We have top scientists working on that right now.

[C]

How can you be cold? You're wearing boots, thermal socks, and three blankets. How are your feet cold? Impossible.

[B]

So we may have talked about this in another explainer, Chuck. I'm not sure. But you will feel cold if you are losing heat to your environment.

[C]

Right.

[B]

And you will feel warm if you are gaining heat from the environment, or if your heat does not lose to the environment, has a hard time leaving your body going into the environment.

[C]

Yeah, we talked about that during wind chills.

[B]

Well, windshield. We did talk about that. That's right.

[C]

We talked about that during windchills.

[B]

I had some memory of that. So, warm mittens. You know what makes mittens warm? They keep in your fingers touching each other.

[C]

Right.

[B]

In a mitten, when one finger loses heat, it goes to the next finger.

[C]

Right.

[B]

Well, you want that heat so you're radiating to yourself inside the mitten. Right. Whereas gloves, where all your fingers are separated, it's trying to prevent your skin from making thermal contact with the air. But you have all this surface area on each finger for each finger of the glove. And so that's why it's harder to keep your fingers warm in gloves than it does in mittens. That's all this is ever doing.

[C]

And that's a wonderful metaphor for where we are in America right now. America, the country that prides itself on being a glove, where each finger is independent of one another, when right now, what we really need to be is a mitten. Each one of us giving heat to one another, relying upon each other in order to be warm together.

[B]

So kumbaya.

[C]

Oh, I'm sorry,

[B]

Chuck. I didn't think he had it in here. Chuck, that was beautiful. That'd be beautiful.

[C]

Kumbaya is great. I forgot about that.

[B]

But. But what?

[C]

That.

[B]

But what that means is if you jump into. If you, if you have a partner in bed who's been there for some time, holding aside your wife's feet, which top researchers are still working on, if you have a partner that's been in bed under the covers, under the, quote, warm blanket, and you've been outside and you feel cold because you're losing heat faster than your body is comfortable, and you say, I'm going to jump in bed. The moment you jump in bed, you will touch your partner and start taking heat from them, Right? The moment you start taking heat from them, you feel warm. You say, oh, honey, you're warm. And what do you feel like to her? Oh, my gosh.

[C]

What I feel like to her is a call to her divorce lawyer.

[B]

So you're taking heat from her. The fact that she's losing heat from, from you means she feels cold, right? So two people cannot feel warm with each other at the same time. You can be neutral. One will feel cold, the other hot. One will feel hot, the other cold. But you both can't feel warm touching each other. Thermodynamically, that's not possible. Nor can you both feel cold touching each other. Somebody is either neutral or somebody's taking heat from the other.

[C]

Right? Well, judging on my marriage, clearly we know who's going to be taking what

[B]

from whom, what kind of heat energy, who's got what?

[C]

I'm just saying.

[B]

So that's it. That's all I got to say about, about blankets.

[C]

All right, you pulled it off. I'm going to give it to you.

[B]

So think of it not as a warm blanket, just as a blanket, as a blanket serving as a thermos in your life to keep the cold beer cold or the hot or you warm at your body temperature. One last thing before we wrap. Reptiles are the same temperature as their environment because they're cold blooded. That's what cold blooded means. It doesn't mean the blood is cold, it just means they don't regulate it and make it a higher temperature so it's the same temperature as the air. So you could put a blanket on a reptile, but it'll be vastly yet less useful to it than if it were warm blooded.

[C]

Well, now I feel bad about making my iguana wear a sweater. Damn. All that for nothing. All that knitting for nothing.

[B]

How much knitting could that have been? And just quickly, if the iguana goes out into the cold weather, you're going to want to bring him a spot sweater because then they will be losing their body heat to the air and maybe they don't want to do that at that moment.

[C]

Right.

[B]

Okay. Because they live that way. But maybe they want to stay warm. And snakes. You ever see snakes in the summertime? They'll come out and sunbathe on the rocks because that feels good.

[C]

Right?

[B]

But that's because a source of energy is being handed to them by sunlight. You can't just give a blanket to a snake and say you don't need the sunlight, just snuggle up in the blanket. That's not going to work.

[C]

Right. And the reason why you don't give a blanket to a snake is because they're a snake.

[B]

Thanks for figuring that one out, Chuck.

[C]

Right. They just. They don't deserve anything. Damn it.

[B]

Don't give a blanket to a snake because it's a snake. What kind of reasoning is that?

[C]

I don't like snakes. That's where that reason it comes from. It's that simple.

[B]

All right.

[C]

There you go. And what I learned is this. If you are using a blanket to keep your beer warm, I invite you to a little place called Walmart or Target to buy a cooler.

[B]

Because you wouldn't use the blanket to keep your beer warm. You use the blanket to keep.

[C]

I'm sorry. I said it wrong.

[A]

Damn it.

[B]

Damn.

[C]

I messed it up. Damn. Anyway. Oh, well. All right.

[B]

We good, Chuck?

[C]

This is great.

[B]

Startalk explainers over and out. Keep looking up.

[A]

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