Name: What Does the Atmosphere Do? Crash Course Geography #6
Uploaded: 2022-06-03T10:19:57.000Z
Duration: 10 min 42 s
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Here side by side we see all of life...and life in its smallest package: a single cell.

Like an intricate fractal, when we zoom in and out, the structures of life don't look

What allows both these structures to survive is a thin layer of protection. The cell's

membrane, or outer barrier, selectively filters what goes in and out of the cell. 

For Earth, we have our atmosphere, or the envelope of gases held around the planet by

gravity, that acts as “the world's biggest membrane.” 

The physician and writer Lewis Thomas most famously made this comparison in 1973. Like

a cell membrane, the atmosphere filters what's allowed in and out, like different wavelengths

Thomas marveled at how photographs like the famous “Earthrise” showed the sterile

surface of the moon with the “exuberant” Earth rising in the background. It seemed

miraculous that the Earth was so alive while everything around it seemed so...not.

Most of us take the atmosphere for granted and rarely think about what it's made of

or how it moves or changes. We notice it when bad weather inconveniences us or appreciate

it when enjoying the outdoors. But it's been 5 billion years in the making and it's

how we and every other cell of life are able to survive. 

I'm Alizé Carrère and this is Crash Course Geography.

Earth's atmosphere is a unique reservoir that forms a protective boundary between outer

space and the biosphere, which is where all life exists on Earth's surface.

Air is really a mixture of gases that are odorless, tasteless, colorless, formless,

and blend together so well they tend to act like a single gas. 

The recipe close to the Earth's surface is 99% nitrogen and oxygen, slightly less than

1% argon, and a tiny percent of volume comes from minor gases, like carbon dioxide. But

this mostly consistent mixture starts to deviate as we get towards the outer edge of the atmosphere. 

To better study the progression, we can break up the atmosphere into vertical layers or

“spheres” using several different characteristics. 

The four layers we hear most about are the troposphere, stratosphere, mesosphere, and

thermosphere, and they come from studying the atmosphere based on its temperature structure.

Each layer has a different starting temperature that decreases or increases as we move towards

Temperature even affects the thickness of the layers. The layer closest to the Earth

where all weather and most of the air molecules exist -- the troposphere -- can extend out

anywhere from 8 to 16 kilometers above the surface, depending on the season or latitude

That sounds kind of arbitrary, but it's really just physics: when the air molecules

are cold, they huddle together, making the air denser and more compact. So in winter

or near the poles, the troposphere is thinnest. And it's thickest where the air molecules

spread out, like in warm places at the equator. 

When we move to the stratosphere, the next layer, temperatures tend to be layered and

get progressively warmer. Here we have the ozone layer, which is the section of the atmosphere

with the highest concentration of ozone, one of the minor gases in our recipe.

The ozone layer lets the wavelengths of light conducive to life to pass through, while filtering

out those that are harmful, like most of the ultraviolet waves. Absorbing UV rays is what

causes temperatures to increase in the stratosphere. 

Then temperatures drop in the mesosphere and increase again in the incredibly hot thermosphere

where the few air molecules floating around out there can get to be 1,100 degrees Celsius! 

Altogether, the atmosphere extends 480 kilometers above Earth's surface. Which sounds like

a lot, but the diameter of the Earth is 12,756 kilometers. Compared to that, the atmosphere

This thin layer of gas is so critical for life to exist, which is why it's so important

to talk about early on in our journey into physical geography. 

Without the atmosphere, none of the processes we'll study in the hydrosphere, lithosphere,

Energy from the Sun is constantly passing through the different layers of the atmosphere

as waves, landing on and being absorbed into the Earth's surface to provide the heat

Really, that “energy” is electromagnetic radiation, or different wavelengths of energy

that travel away from the surface of an object. All objects -- the Sun, the Earth, our skin

-- are constantly emitting waves of electromagnetic radiation. 

Very hot and high energy objects, like the Sun, emit vast amounts of energy as short

wavelengths, or solar radiation, in the form of light. Cooler objects, like the Earth,

emit much longer heat waves, or terrestrial radiation. 

Since there's constant sunlight passing through the atmosphere, we might expect temperatures

to keep increasing, like when you're sitting under a blanket and get so hot that you want

Fortunately, the Earth doesn't get swelteringly hot because the Earth and the atmosphere naturally

balance the shortwave solar energy that arrives with the longwave energy sent back to space.

This is the atmospheric energy budget, which is achieved with three common types of energy

The first type of energy transfer is that radiation we've been talking about, which

is more generally the transfer of energy through waves. Like when we warm our hands over a

campfire. Insolation, or incoming solar radiation, reaches us by -- you guessed it! -- radiation. 

Imagine we're riding a sunbeam of solar radiation, trying to navigate the atmosphere

as it hurtles towards the surface. The atmosphere protects the Earth by filtering sunlight,

so there are quite a few obstacles to make it through. 

If our sunbeam has 100 units of radiant energy, most of those units will be intercepted before

we make it to the surface. Let's go to the Thought Bubble.

The outer layer of the Sun is extremely hot thanks to its intense energy, so our sunbeam

This radiant energy can pass easily through oxygen and nitrogen molecules because they're

basically little tiny windows letting short-wave energy in and out. 

But other gases throughout the atmosphere absorb short-wave energy like a sponge filling

In the stratosphere, ozone is a major obstacle. 

And in the troposphere, water vapor in the clouds is the enemy. 

Overall, 19 units of radiant energy from our sunbeam are intercepted by absorption. 

Other particles in the air are pesky, too! 

Dust, smoke, and volcanic emissions scatter radiation and change the direction of the

light's movement without altering its wavelength. 

8 units of energy from our sunbeam will get returned to space, while 20 units will get

scattered as diffuse radiation but persevere to reach Earth's surface.

At this point, 53% of our sunbeam is still headed towards the Earth's surface. 

Thick clouds are actually capable of reflecting up to 80 percent of total incoming radiation,

like a mirror bouncing the energy back into space. 

And even when we make it to the surface, our sunbeam isn't safe -- the ground can reflect

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