Ever wondered about what’s going on in the sky?
If you can remember middle school Physics, you might be able to cast your mind back to what’s known as our atmosphere, a layer of gases that are held in place by gravity and surround Earth.
Serving to keep us humans safe by creating a certain kind of pressure, it is the reason liquid water is able to exist on the planet’s surface, and it also reduces the extremes of temperature differences between the day and night.
Initially made up primarily of hydrogen, the Earth’s atmosphere has significantly evolved since its formation, changing hugely and dramatically as a result of several events in the past few billion years.
So, what does it look like today?
Defining The Atmosphere
As a general rule, air pressure and density will decrease as altitude in the atmosphere increases, though measuring temperature is complicated because it can fluctuate or remain constant depending on the region.
As a result, however, it provides a useful distinction between the layers, as the temperature/altitude profile, also known as the lapse rate, stays the same. Therefore, the atmosphere is divided into five main layers, known as atmospheric stratification.
Let’s take a look at each one:
Troposphere (0 to 12 kilometers)
As the lowest, and perhaps most important, layer of our atmosphere, the troposphere is the section in which we live, and is therefore responsible for the majority of our weather experiences, including rain, snow and clouds.
This section contains approximately 75% of air found in the entire atmosphere, as well as the majority of the water vapor that creates clouds and rain.
Its lowest area is referred to as the boundary layer, whilst is top is known as the tropopause.As the distance above Earth increases, the temperature decreases around 6.5 degrees centigrade per kilometer, though the specific change is determined each day as a result of the weather we are experiencing.
This decrease is a result of experiencing less pressure at higher altitudes - if air moves upwards, the lower pressure causes it to expand, which also results in a cooling effect. As a result, it gets colder the further you get from the troposphere.
Stratosphere (12 to 50 kilometers)
Covering around 50 kilometers above the tropopause, the Stratosphere is easily the most recognizable layer of the atmosphere, as it contains much of our ozone layer, absorbing dangerous and potentially life threatening rays of UV radiation.
It shields us vulnerable humans and our fragile skin from illnesses such as cancer and other health issues, but as you may have heard, the chemicals we produce here on Earth known as CFCs (or freons and halons) have been breaking it down.
This has resulted in what is known as a ‘hole in the ozone’, located in the Antarctic - because humans have largely stopped producing the majority of CFCs responsible for this damage, however, we are hopeful that this hole will eventually close up.
Mesosphere (50 to 80 kilometers)
Directly above the Stratosphere, you’ll find the Mesosphere, reaching absolutely freezing temperatures at an average of around -130 degrees Fahrenheit. The very top of this layer, the mesopause, is the coldest part of the whole atmosphere.
As a result of these uninhabitable conditions, it’s a very difficult layer to study, as neither balloons nor jets can reach high enough altitudes to enter it, whilst space shuttles and satellites are unfortunately orbiting too high above it.
One thing we do know for certain, though, is that meteors entering this layer will burn up upon reaching it.
Thermosphere (80 to 700 kilometers)
Once you hit the fourth layer of the atmosphere, things start hotting up a bit, hence the name. In the thermosphere, temperatures can hit as painfully hot as 2,700 degrees Fahrenheit.
This is the layer in which the International Space Station orbits our Earth, as although it’s considered part of our atmosphere, the incredibly low air density results in the majority of this layer being referred to as Outer Space.
If you’ve ever seen the beauty and wonder of the Northern Lights, also known as the Aurora Borealis, this is the level of the atmosphere where those beautiful auroras occur, as a result of collisions between charged particles, atoms and molecules.
Exosphere (700 to 10,000 kilometers)
Last but not least comes the Exosphere, the outmost layer or the very limit of our atmosphere, extending out from the top of the Thermosphere in an area called the exobase, which continues for thousands of kilometers until it merges with solar wind.
Comprised mostly of oxygen, hydrogen and helium atoms, though also featuring heavier molecules like nitrogen, oxygen and carbon dioxide towards its base, these atoms and molecules are very distanced from one another.
As a result, they can travel huge amounts, across hundreds of kilometers, without experiencing any collisions, which means that the particles are constantly escaping into space, as the exosphere itself does not behave in the manner of a gas.
Because it’s located so high above the Earth, there are no phenomena produced as in the Thermosphere, though occasionally the Aurora Borealis does occur in its lower half, where the exosphere and thermosphere overlap.
An interesting fact about the exosphere is that it is home to the majority of satellites that orbit our Earth, so it’s very likely the location of your WiFi, television and cellphone signals. So that’s where they come from!
Whilst these five main layers are classified by temperature, it’s possible to identify several more secondary layers, which are separated by other properties. These are known as the ozone layer, the ionosphere, the hoosphere and heterosphere.
We recognize the ozone layer as within the stratosphere, whilst the ionosphere refers to a section of the atmosphere overal that has been ionized by radiation from the sun, as it is responsible for creating auroras.
Serving to indicate if atmospheric gases within them are well mixed, the layers known as the homosphere and heterosphere respectively encompas most of the atmosphere, touching the area accepted generally as the very edge of space.