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Transcript

The Atmosphere – Layers of Air · Talking Science

0:00
I want you to do something for a second. Just
0:03
look around the room you're sitting in right
0:04
now. Yeah, take a really good look at the space
0:07
between you and the wall. Right, or like between
0:09
you and your screen. Because it looks entirely
0:11
empty, you know? Up until I sat down with the
0:14
sources for today's deep dive, I always just
0:17
thought of that space as, well, just a void that
0:20
we happen to walk through. Like it's the default
0:21
setting of the universe or something. Exactly.
0:24
But the central premise we are exploring today...
0:27
It completely shatters that illusion because
0:30
right now you are sitting at the bottom of an
0:33
ocean, not an ocean of water, obviously, but
0:37
a literal physical ocean of air. And we are so
0:40
habituated to its presence, right, that we're
0:43
entirely blind to it. We treat the atmosphere
0:45
as an absence of stuff. Yeah. But it is a tangible
0:49
physical substance. I mean, it has mass, it has
0:51
structure, and crucially, it has weight. Which
0:53
is wild to think about. It really is. Like, if
0:55
you were to take a standard -sized living room
0:57
and weigh just the air inside of it, you would
0:59
find it weighs about 100 pounds. Okay, wait,
1:01
hold on. If there's 100 pounds of invisible stuff
1:05
just sitting in my living room and, you know,
1:09
Miles of this stuff stacked on top of my head.
1:12
Why don't I feel heavy? Right. That's the natural
1:15
question. I mean, I can wave my hand in front
1:17
of my face and feel almost zero resistance. So
1:19
if I'm at the bottom of an ocean of weight, why
1:21
aren't we all just being crushed? Well, the simple
1:24
answer is internal pressure. The human body evolved
1:27
at the very bottom of this specific ocean. So
1:30
the fluids and gases inside your body are actually
1:33
pushing outward with the exact same force the
1:36
atmosphere is pushing inward. Oh, wow. Yeah,
1:38
it's this perfect equilibrium. But that immense
1:41
weight is always there, pressing down on every
1:44
square inch of you at roughly... 14 .7 pounds
1:48
per square inch. That is almost claustrophobic
1:50
when you actually stop to visualize it. It really
1:52
changes your perspective. It does. I've spent
1:54
my whole life treating the air like this passive
1:58
backdrop. So the goal for this deep dive is to
2:01
stop taking this invisible ocean for granted
2:04
and to understand what it actually is, how it's
2:06
built, and how it literally colors our world.
2:09
I love that. So let's start with the recipe.
2:11
What are we actually swimming in? Because honestly,
2:15
if you'd asked me yesterday, I would have confidently
2:17
said we are swimming in oxygen. And you would
2:19
be joining a vast majority of people who think
2:21
the exact same thing. It just makes sense, right?
2:24
It does, because we require oxygen to survive,
2:26
so our brains just assume that's the primary
2:28
ingredient of the air around us. But oxygen only
2:31
makes up about 21 % of the atmosphere. Which
2:33
leaves a massive chunk unaccounted for. Right.
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Almost all the rest, about 78%, is actually nitrogen.
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70%. Yep. And nitrogen is largely defined by
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what it doesn't do. What do you mean? Well, it's
2:46
highly unreactive. It mostly just sits there
2:48
diluting the oxygen. And honestly, we should
2:50
be very thankful for that dilution. Why is that?
2:53
If our atmosphere was purely oxygen, the world
2:57
would be incredibly flammable. Like a single
3:00
spark would ignite massive, uncontrollable firestorms
3:03
everywhere. Oh, wow. Okay, so the air is essentially
3:06
a giant smoothie and the nitrogen is the ice.
3:09
The ice. Yeah, like it's the filler giving the
3:11
drink volume so the active ingredients aren't
3:13
so intense that they burn the house down. That
3:16
is actually a highly accurate way to look at
3:18
it. The nitrogen provides the safe bulk. So you've
3:21
got 78 % nitrogen, 21 % oxygen. Right. That leaves
3:25
just about 1 % of the atmosphere. And this tiny
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remaining fraction is made up of what scientists
3:31
call trace gases. Trace gases. Now, my assumption
3:35
is that if something is a trace amount, it's
3:38
basically a rounding error. Yeah. You know, like
3:40
it shouldn't matter that much. It sounds like
3:42
it shouldn't matter. Yeah. But that one percent
3:43
dictates the climate of the entire planet. Really?
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Absolutely. This fraction includes a gas called
3:49
argon, along with water vapor and carbon dioxide.
3:53
And carbon dioxide is the perfect example of
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something punching far above its weight class.
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Well, it makes up just a microscopic fraction
4:00
of the air, about 0 .04 percent. Yet it is the
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primary thermostat for Earth. OK, I need to push
4:07
back on that for a second because the math. feels
4:09
completely counterintuitive. How can 0 .04 %
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of anything control the temperature of an entire
4:16
planet? It's crazy, right? It all comes down
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to molecular structure. Carbon dioxide molecules
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have a very specific physical property. When
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visible light from the sun hits the Earth, it
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passes right through the carbon dioxide. It doesn't
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interact with it at all. It just goes right past.
4:32
Exactly. The sunlight warms the surface of the
4:35
Earth, but when the Earth tries to radiate that
4:38
heat back out into space, the heat takes a different
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form. it becomes infrared radiation. So the energy
4:44
actually changes shape after it hits the ground.
4:46
Yes, exactly. And carbon dioxide molecules are
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highly reactive to infrared radiation. Oh, I
4:52
see. So when that heat tries to leave, the CO2
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molecules absorb it. They physically vibrate,
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and in doing so, they radiate that heat back
5:00
down toward the surface. Even at microscopic
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concentrations, there are enough of these molecules
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forming this invisible thermal blanket that keeps
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the heat from escaping. It's the reason Earth
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isn't just a frozen, lifeless rock. It's basically
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a one -way mirror for heat. Like the sun's energy
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can check in, but a lot of it can't check out.
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A one -way mirror is a great visual. And because
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that trace amount is so incredibly powerful,
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even tiny adjustments to that 0 .04 % have massive
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cascading planetary consequences. It's staggering
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to realize our entire existence relies on such
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a delicate chemical balance. It really is. So
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we have this mix, right? The nitrogen ice, the
5:41
oxygen flavor, and the highly potent trace gases.
5:45
But the sheer mass of all this gas settling onto
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the planet means it isn't just swirling around
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randomly. Right. It's highly structured. Yeah,
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it settles into highly organized layers. The
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source text described it like a layer cake, where
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each level has a completely different physical
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reality. Yeah, the layer cake analogy is perfect.
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We start at the very bottom layer, the one we
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are physically sitting in right now. It's called
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the troposphere. The troposphere. Right. Every
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mountain, every forest, every city exists here.
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And crucially, it is where all of our weather
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happens. All of it. All of it. The clouds, the
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hurricanes, the gentle spring rain. That is all
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just the troposphere churning and boiling. You
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know, the scale of this layer gave me vertigo
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when I read it. Because when you stand outside
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and look up at a massive towering thundercloud.
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Yeah. It feels like the sky goes up forever.
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It does feel endless. But the troposphere is
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shockingly thin. It's only about 10 to 15 kilometers
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thick. It totally shatters the illusion of an
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endless sky. It really does. Yeah. cannot stop
6:45
thinking about. If I could get into my car and
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somehow drive straight up into the sky at highway
6:49
speeds, my normal daily commute would literally
6:53
take me out of the weather entirely. Yeah, you'd
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just punch right through. Like 10 or 15 minutes
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of driving and I'd be through the roof of the
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troposphere. It just makes this environment we
7:01
live in feel incredibly small. It really is a
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thin bubble, but if you keep driving your imaginary
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car upward, you cross a boundary into the stratosphere.
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Okay, the stratosphere. And because it sits above
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the churning heat of the Earth's surface, it
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is incredibly stable. There's almost no vertical
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movement of air, which means there are no storms,
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no clouds, no weather. Which totally explains
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why commercial airliners climb to 35 ,000 feet.
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Exactly. They are literally climbing out of the
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troposphere to skim along the bottom of the stratosphere
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just to avoid the weather. Yeah, they want that
7:33
smooth, stable air. But the stratosphere does
7:36
something much more vital for us than just provide
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a smooth flight. It contains the ozone layer.
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Right, the famous ozone layer. Ozone is a molecule
7:44
made of three oxygen atoms bound together, and
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it acts as the Earth's biological shield. We
7:50
throw that term around constantly, usually in
7:52
the context of it being damaged, you know. But
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how does an invisible gas actually act as a shield
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against something as powerful as solar radiation?
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It's actually a process of sacrifice. Sacrifice.
8:03
Yeah. When high -energy ultraviolet radiation
8:05
from the sun slams into the stratosphere, it
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hits these ozone molecules. The ozone absorbs
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that immense energy, and the molecule is physically
8:13
shattered apart by the impact. Wow, so it takes
8:16
the bullet for us. It literally does. And then,
8:19
through natural chemical reactions, those shattered
8:22
pieces eventually recombine back into a new ozone
8:25
molecule, ready to take another hit. That is
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incredible. It's a continuous cycle. Without
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that invisible layer of molecules constantly
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shattering and reforming, the surface of the
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Earth would be sterilized by UV radiation. Okay,
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so... The stratosphere is handling the energy
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and the radiation from space. But space isn't
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just radiation. No, definitely not. It's full
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of actual physical garbage, right? Right. Rocks,
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dust, ice. Does the atmosphere do anything to
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protect us from the physical stuff falling in
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our heads? That brings us to the next layer up,
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the mesosphere. The mesosphere. This is a much
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colder, thinner layer of gas, but it acts as
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a cosmic incinerator. When space debris... you
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know, meteors fall toward Earth, they're traveling
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at tens of thousands of miles an hour. When they
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hit the mesosphere, they vaporize. See, I struggle
9:13
with the physics here. If the air in the mesosphere
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is incredibly thin, which it must be, since it's
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so high up, how is there enough friction to completely
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vaporize a solid rock? It's a common misconception
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that it's just friction. Oh, it isn't? No, it
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is primarily something called ram pressure. Ram
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pressure. Because the meteor is moving at such
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an extreme velocity, the thin air in front of
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it simply cannot get out of the way fast enough,
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so the air is violently compressed. And in physics,
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when you rapidly compress a gas, it heats up.
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So the meteor isn't rubbing against the air,
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it's squishing the air into a superheated plasma
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wall. Exactly that. The air in front of the meteor
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reaches thousands of degrees and that intense
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heat melts and vaporizes the rock. That is wild.
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So those beautiful romantic shooting stars you
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see at night, that is just ram pressure in the
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mesosphere destroying a rock before it can hit
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the ground. The atmosphere is doing an unbelievable
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amount of heavy lifting. We have the weather
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layer, the radiation shield. And the rock incinerator.
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And one final highly active layer above that,
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the thermosphere. Thermosphere. The gas here
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is so incredibly sparse that you would consider
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it a vacuum in any laboratory on Earth. But it
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is here that the solar wind interacts with the
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scattered molecules to create the auroras, you
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know, the northern and southern lights. Oh, beautiful.
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And if you look up and see the International
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Space Station moving across the night sky, it
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is orbiting within the thermosphere. Wait, hold
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on. If the space station is in the thermosphere
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and the thermosphere is part of the atmosphere,
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is the space station actually in space? Like,
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where is the boundary line? Well, there is no
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solid border. The atmosphere doesn't just hit
10:53
a brick wall and turn into the vacuum of space.
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It doesn't. No, it just slowly, gradually fades
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away. The molecules get further and further apart
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until they are essentially gone. So the space
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station is in space, but there are still enough
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stray air molecules up there that they create
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microscopic drag on the station, slowly pulling
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it down. Oh, I had no idea. Yeah, that's why
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it has to occasionally fire its thrusters to
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boost itself back up. Which brings up a massive
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question for me. If there is no lid on the...
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the atmosphere and it just fades into an empty
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vacuum, why doesn't it all just float away? We
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circle right back to where we started, weight
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and gravity. Because air is a physical substance
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with mass, the Earth's gravity pulls on it, anchoring
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it to the planet. So it sounds like stacking
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a hundred fluffy pillows on top of each other.
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Oh, I like that. Yeah, like the pillow at the
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very bottom of the pile where we're sitting is
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going to be squished completely flat by the sheer
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weight. of the 99 pillows on top of it. Right.
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So it's dense and compacted. But as you climb
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up the pile, there's less weight pressing down.
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The pillows in the middle are fluffier and the
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one at the very top is completely unsquished,
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just barely resting there before floating off.
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That is the perfect way to visualize atmospheric
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density. The weight of all those upper layers
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squeezes the molecules at sea level tightly together.
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Yeah. And as you move higher, climbing up your
12:12
pile of pillows, the pressure drops, the molecules
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spread out. And the air thins. Which completely
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explains why high -altitude mountain climbers
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are always gasping for breath. The recipe of
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the air hasn't changed. It's still 21 % oxygen.
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But the air is so fluffy and spread out that
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every physical breath pulls in drastically fewer
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oxygen molecules. Exactly. Their lungs are trying
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to operate in an environment they aren't calibrated
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for. The pressure simply isn't there to pack
12:41
the oxygen densely into their bloodstream. So
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down here at the bottom of the pillow pile, we
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have this dense, squeezed obstacle course of
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nitrogen and oxygen molecules. Right. What happens
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when something tries to pass through this obstacle
12:54
course, like sunlight? Because this brings us
12:57
to the physics of color and the ultimate childhood
13:00
question, why is the sky blue? It is the question
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every parent dreads, but the physics behind it
13:06
are incredibly elegant. I can't wait. First,
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we have to look at the sunlight itself. The light
13:11
pouring out of the sun looks white to us, but
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white light is actually a bundle of all the colors
13:16
of the rainbow traveling together. We see that
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when light hits a prism or a raindrop and fractures
13:20
into a rainbow. Yes. And light travels in waves.
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The crucial detail here is that each of those
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colors has a different physical wavelength. Okay.
13:30
Red light travels in long, sweeping, lazy waves.
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Blue light travels in much shorter, choppier,
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tighter waves. So we have this bundle of different
13:40
sized waves crashing into the top of the atmosphere.
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And as they push down into that dense lower layer,
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they start hitting things. They hit those tightly
13:48
packed nitrogen and oxygen molecules. Right,
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the obstacle course. When light hits an object
13:53
in the air, a process called scattering occurs.
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The light bounces off the molecule and ricochets
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in a new direction. But the molecules don't treat
14:01
all the colors equally. Not at all. Think of
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the light waves like water waves hitting a small
14:05
rock in the ocean. Okay. A massive long ocean
14:08
swell, which represents our red light, will just
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wash right over the rock undisturbed. It pushes
14:13
straight through. Got it. But tiny choppy ripples,
14:16
our blue light, will hit the rock and splash
14:18
everywhere. Because the blue wavelengths are
14:21
so short, they constantly crash into the air
14:23
molecules. The blue light bounces from molecule
14:26
to molecule, scattering wildly across the entire
14:28
sky. It's like a massive game of pinball. The
14:32
blue light is the ball constantly hitting the
14:34
bumpers, lighting up the entire board, while
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the red light is heavy enough to just drop straight
14:38
down the middle without touching the sides. A
14:40
planetary game of pinball, yes. When you look
14:43
up at the sky during the day, you aren't seeing
14:45
an empty blue void. You are physically seeing
14:49
that scattered blue light ricocheting around
14:51
the dense lower layers of our air. I feel a profound
14:54
sense of satisfaction finally understanding the
14:57
mechanics of that. It's pretty cool. But if the
14:59
sky is a blue pinball machine, What happens at
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sunset? Why does the sky suddenly turn into this
15:04
dramatic painting of fiery reds, oranges, and
15:07
purples? The beauty of this is that the exact
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same physics explains both. Yeah, nothing about
15:13
the air changes. What changes is the geometry
15:15
of the light's path. At noon, the sun is directly
15:18
overhead. The light takes a short, straight shot.
15:22
down through the atmosphere to reach your eyes.
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So it only has to travel through that 10 -mile
15:26
slice of the troposphere. Right. But as the sun
15:29
lowers toward the horizon, the angle changes.
15:33
The light is no longer coming straight down.
15:35
It is coming at us from a severe sideways angle.
15:38
Okay, I see where this is going. That means the
15:40
light has to push through a much thicker, longer
15:43
slice of the atmosphere to reach you. The pinball
15:46
board just got 10 times longer. And along that
15:48
much longer journey, the blue light is still
15:51
hitting the bumpers. It's still scattering wildly.
15:53
But because the path is so long, the blue light
15:56
scatters so much that it is completely exhausted.
15:59
Oh, wow. It scatters away in other directions
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before it can ever reach your eyes. The blue
16:04
is entirely filtered out. Exactly, leaving only
16:06
the longer wavelengths, the reds and the oranges.
16:09
The long ocean swells. Right, the swells that
16:11
wash over the obstacles. They are the only light
16:14
strong enough to push straight through that thick,
16:16
horizontal slice of atmosphere. A beautiful red
16:19
sunset is literally just the leftover light,
16:23
the survivors of a long journey through the air.
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Leftover light. That is an incredibly poetic
16:29
way to view it. The same light, the same gas,
16:31
just a different angle causing a completely different
16:34
visual experience. It's amazing. It really drives
16:37
home just how active and dynamic the air is.
16:39
It's performing complex physics every single
16:42
second. Yeah. But, you know, it feels like this
16:45
environment is almost too perfectly tailored
16:47
for us. The sources point out that this wasn't
16:49
the original recipe, was it? No, not at all.
16:52
The early Earth would have been a toxic, unrecognizable
16:55
nightmare. There was no breathable atmosphere,
16:58
no protective ozone, no blue skies. What was
17:00
it then? The atmosphere was mostly carbon dioxide,
17:03
methane, and ammonia belched out by early volcanoes.
17:06
It would have choked us in seconds. So how do
17:08
we get from a volcanic nightmare to the perfectly
17:11
balanced, oxygen -rich environment we have today?
17:13
We owe our existence to biology. Biology? Yeah.
17:19
Billions of years ago, the very first tiny living
17:21
things microbes in the early oceans developed
17:24
the ability to photosynthesize. They took in
17:27
sunlight and the abundant carbon dioxide, and
17:31
as a waste product, they released oxygen. A gas
17:33
that didn't even exist in the atmosphere before
17:36
them. Not in any meaningful quantity, no. Generation
17:38
after generation, for billions of years, these
17:41
microscopic organisms quietly pumped oxygen into
17:45
the sky. They essentially terraformed the planet.
17:49
Life itself manufactured the breathable atmosphere.
17:52
I'm having a bit of a crisis realizing this.
17:54
There's a lot to take in. We constantly treat
17:55
the atmosphere like this passive backdrop that
17:58
just happened to be here waiting for us. But
18:00
it is an active... hardworking life support machine
18:03
built by biology. That's exactly what it is.
18:06
Let's just look at his resume for a second, because
18:07
the list of things it does is staggering. The
18:10
mesosphere acts as a cosmic incinerator, vaporizing
18:13
space debris. And the stratosphere houses the
18:16
ozone layer, taking the bullet from the sun's
18:18
radiation so the surface doesn't get sterilized.
18:21
The trace gases trap just enough heat to keep
18:23
the oceans liquid and the planet habitable. And
18:26
the troposphere acts as a global transit system
18:29
for fresh water, ferrying water vapor around
18:32
the globe and dropping it as rain to water our
18:35
crops and fill our rivers. It's insane. If any
18:38
single one of those systems fails, the planet
18:40
quickly becomes hostile to life. It is a perfectly
18:44
calibrated machine. It really is. And as we step
18:48
back to look at the whole picture, there's a
18:50
final sense of scale that the sources provide,
18:53
which is vital to understand. Okay, what's that?
18:55
Because when you stand in a field and look up
18:58
at a clear blue sky, the atmosphere feels limitless,
19:02
right? It feels so vast that nothing we do down
19:05
here could possibly impact it. Right. But relative
19:08
to the size of the planet, it is shockingly thin.
19:11
How thin are we actually talking? Imagine you
19:13
could shrink the entire Earth down until it was
19:15
the exact size of an apple and you're holding
19:17
it in the palm of your hand. Okay, I have the
19:19
apple. If Earth were that apple, the entire atmosphere,
19:22
the layer holding all our weather, all our breathable
19:24
oxygen, every cloud, bird, and commercial airplane
19:27
would be thinner than the skin of the apple.
19:30
Thinner than the skin of an apple. Astronauts
19:32
talk about this phenomenon constantly. It's called
19:34
the overview effect. The overview effect. Yeah.
19:37
When they arrive at the space station and look
19:38
back at Earth, they expect to see an endless
19:41
sky. Instead, they see this delicate, glowing,
19:44
incredibly thin sliver hugging the edge of a
19:47
massive rock against the black void of space.
19:50
That sounds beautiful. They frequently remark
19:52
on how fragile it looks and how seeing that thin
19:54
blue skin completely rewires their brain regarding
19:58
how we treat it. It's terrifying, but it also
20:00
instills a deep sense of awe. I want to leave
20:03
you, the listener, with a final thought to mull
20:05
over today as you go about your routine. Yeah.
20:08
Think about that apple skin. Every breath ever
20:11
taken by every human, every animal, every dinosaur,
20:14
every living thing in the history of this planet
20:16
has happened inside that microscopic, fragile,
20:19
glowing sliver of gas. It's humbling. It really
20:22
is. And if our entire existence relies on a layer
20:25
thinner than an apple skin, how much more carefully
20:28
should we be thinking about altering that tiny
20:30
1 % of trace gases that keeps the whole system
20:33
balanced? It is a question that requires our
20:36
full attention, absolutely. Thank you for joining
20:38
us on this deep dive. The next time you step
20:41
outside, I challenge you to really look up. Look
20:45
at the scattered blue light ricocheting around
20:47
the pinball machine. Feel the pressure of the
20:49
ocean stacking up above you. Stop taking the
20:52
void for granted and really see the ocean you
20:55
are walking around in. We'll catch you next time.