Atmospheric Layers
The atmosphere is made up of layers of gases. There are five principal atmospheric layers and inside them are thinner sub-layers.
The five principal atmospheric layers are namely, starting from the one nearest the surface of the Earth upwards, the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
Although the heights of each layer can vary due to changing weather and climate conditions, we can approximate their values to the following: the Troposphere extends up to 20 km above sea level, the Stratosphere up to 50 km, the Mesosphere up to 85 km, the Thermosphere up to 690 km, and the Exosphere up to 10,000 km.
Because of the pull of gravity, a significant fraction of the gases that make up the atmosphere are found in the lower layers; mostly, the Troposphere being the lowest of all. The heavy gases are found here while the much lighter gases, which don't experience the same amount of 'pull' of gravity, are found in higher altitudes.
In fact, approximately 80% of the total mass of the atmosphere is concentrated in the Troposphere.
Those who have been monitoring the latest activities with regards to the International Space Station might be familiar with the Thermosphere, being the atmospheric layer where the ISS orbits around the Earth.
Inside the principal layers mentioned above are sub-layers that are classified based on their prominent characteristics. The two most popular of these layers are the ozone layer and the ionosphere.
You've probably heard a lot about the ozone layer in the 80's and early 90's. That's because the excessive emission of ODS (ozone-depleting substances), most notably CFCs (chlorofluorocarbons), created a hole in the ozone layer above the polar regions and increased Earth's exposure to ultraviolet radiation (UV).
The ozone layer, as the name implies, has the highest concentration of ozone among all atmospheric layers. Approximately 90% of all the ozone found in the atmosphere is found in the ozone layer.
Another sub-layer that some of us frequently hear about (at least those fresh from high school) is the the ionosphere. The ionosphere is where the northern and southern polar lights or auroras are found. This atmospheric layer is called the ionosphere because most of the gases here have been ionized due to constant bombardment of solar radiation.
Due to global warming, the lower atmospheric layers are experiencing increased temperatures and is believed to be one of the reasons why we're experiencing extreme weather conditions.
The gas particles in the Exosphere, however, are too far apart to have any significant impact on the Earth's climate and weather conditions.
Compared to the size of the Earth, with a diameter of approximately 12,600 km, the combined thickness of these atmospheric layers (up to the Thermosphere) is nearly negligible. However, as we can see, the health of the atmosphere plays an important role in preserving life in the planet.
Let's take care of it while we still can.
Want to learn more about the atmosphere and air pressure? You can read about both here in Universe Today.
Of course, you can find more info at NASA too. Follow these links:
Earth's Atmosphere
Earth
Tired eyes? We recommend you let your ears do the work for a change. Here are some episodes from Astronomy Cast:
Atmospheres
Plate Tectonics
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