Have you ever looked up at the night sky and wondered about the mysteries of space? Well,
space is closer than you might imagine; it starts just beyond the edge of Earth's atmosphere. But
what exactly is Earth's atmosphere and how does it protect us from the harsh conditions of space?
By the end of this lesson, you'll be able to identify the main components of Earth's
atmosphere and explain the functions and characteristics of each atmospheric layer.
So, have your guided notes ready, and let's take off on a journey through Earth's atmosphere.
In our lesson on Earth's spheres, we learned that the atmosphere is a
system that contains all of Earth's air, or the gases that surround our planet.
Our atmosphere is made up of a combination of gases, including 78 percent nitrogen,
21 percent oxygen, and trace amounts of others, such as carbon dioxide and water vapor.
These gases play an important role in supporting life on our planet.
Most of the gas in our atmosphere is nitrogen. It's essential for the nitrogen cycle,
which transforms the gas into a more usable form that nearly all plants need to grow properly.
Oxygen is necessary for all living things to breathe and survive.
Carbon dioxide helps regulate the Earth's temperature and is necessary for photosynthesis.
Water vapor is a key part of the water cycle and helps regulate
global temperatures, weather, and climate.
Along with gases, air pressure and temperature are also important components of the atmosphere.
We see this same blend of gases throughout the atmosphere, but air pressure and temperature
change as we go higher up. Air pressure is the force caused by the weight of the air.
In our lesson on Earth's oceans, we learned that the weight of the
water adds to the pressure the deeper we travel towards the ocean floor.
Similar to the ocean floor, the Earth's surface is where the air pressure is the greatest.
The gravitational pull of the Earth attracts the molecules of air downward toward the surface,
keeping our atmosphere in place. This pull results in more of these fast-moving atoms bumping into
each other closer to the Earth's surface. Air pressure decreases as you travel higher
up because there are fewer gas molecules bumping into each other. Temperature, on the other hand,
varies or changes in different layers of the atmosphere, which brings us to our next section.
The atmosphere is made up of five main layers. Remember the zones of the ocean?
They change based on the depth below the ocean's surface. The layers of the atmosphere, however,
change based on two things: altitude, or the height above the ground, and temperature.
The first layer is the troposphere, which is closest to the Earth's surface.
This is where we live, and it extends from the ground to about twelve kilometers high. That's
a few kilometers above the tallest mountain in the world, Mount Everest. This layer contains all the
air that living things need to survive and it's where most of our clouds and weather are formed.
The troposphere contains most of the gas in our atmosphere, about 75 percent. That dense
concentration of gases creates a stable layer that supports the flight of birds and planes.
Air pressure is at its highest at the ground and decreases as we travel away
from the surface. The temperature in this layer is warmer near the surface
and colder as we climb. However, this isn't the case for every layer in the atmosphere.
The next layer is the stratosphere. It starts from the top of the troposphere and goes fifty
kilometers high. The stratosphere is home to the ozone layer. This layer is characterized by
a high concentration of molecules that absorb the most harmful ultraviolet radiation from the Sun.
That energy is then turned into heat. Because heat rises and there is no weather
or wind to circulate the molecules, like in the troposphere, we'll find the cooler temperatures
at the bottom of the stratosphere and warmer temperatures near the top.
The mesosphere is above the stratosphere, between fifty and eighty kilometers high. It's very cold
and the air is thin, but there are enough gases in this layer to cause something pretty special:
meteor showers, sometimes referred to as shooting stars. They happen when small space rocks
enter Earth's atmosphere. Once they reach the mesosphere, they burn and glow across the sky due
to the friction and heat generated as they hit the gases in this layer. The mesosphere contains some
of the coldest temperatures in our atmosphere, with an average temperature well below zero.
We'll also find a bit of water vapor here, which forms noctilucent clouds. These are
the highest clouds in the atmosphere and can be seen without a telescope under certain conditions.
It's important to note that over ninety-nine of all the gases in our atmosphere are found in these
first three layers closest to the Earth. What does that tell you about the distance between gas
molecules in the two outer layers? Pause the video here and record your answer in your guided notes.
The outer layers of the atmosphere are huge but they're mostly empty space. There are still some
molecules in these layers, they're just very far apart. The thermosphere is above the mesosphere
from 80 to 700 kilometers high. This is where the northern and southern lights, or the auroras,
happen. They occur due to solar particles interacting with the gases in this layer.
This layer is also where we'll find the International Space Station orbiting the Earth.
The temperature patterns in the thermosphere are similar to the stratosphere, getting
warmer as you go higher. There are very few molecules here but they can get extremely hot,
up to 4,500 degrees Fahrenheit. They're very far apart and rarely bump into each other,
though, so it would still feel very cold in this part of the atmosphere.
Finally, the exosphere is the outermost layer, from 700 to 10
thousand kilometers high. This is where we'll find most of the satellites orbiting Earth.
The gases in this layer are mostly hydrogen and helium and they're very far apart from each other.
Particles from this layer often escape into space.
So, with all these layers, where exactly is the edge of outer space?
10 thousand kilometers sounds really far. Do we really need to go that far to reach space
if the Earth's atmosphere is already so thin by that point? Scientists use a hundred kilometers
above the Earth's surface as a reference point that they call the Kármán Line. The Kármán line
is the altitude at which a spacecraft enters outer space. Why a hundred kilometers? Well, most of the
gases in the atmosphere are found within a hundred kilometers of the Earth's surface, so this is
considered the boundary between Earth's atmosphere and space. That means space technically begins
in the thermosphere. So why is the exosphere considered part of Earth's atmosphere? Even though
the exosphere contains very few molecules, there are still more than there are in space, therefore
it's part of our atmosphere and a transition zone between the upper atmosphere and space.
So, let's go over what we learned today. We now know gases, air pressure,
and temperature are all important components of Earth's atmosphere. The five layers of the
atmosphere are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
The layers of the atmosphere are determined by altitude and temperature.
Lastly, Earth's atmosphere is essential for supporting life on our planet.
Ready to learn even more about our atmosphere? Be sure to check out the
practice questions and extension activities that go with this lesson. And remember,
in earth science as in life, you rock. I'll see you next time.