Different Layers of Earth’s Atmosphere

Introduction

Different layers of earth’s atmosphere play a major role in our daily life. We know that the sunlight we receive on this Earth is actually very harmful. Indeed, if unfiltered, it can even cause skin cancer. So how are humans surviving this onslaught of radiation every day? We are safe because nature has provided us with a shield in the form of the ozone layer, which blocks harmful rays of the sun from reaching the earth.

But this ozone layer is just a small part of the enormous layer of gases that envelops our planet from the surface all the way to almost 10,000 km above sea level. This layer is known as the atmosphere. In this article, we will discuss the atmosphere of the earth in detail.

What is Atmosphere?

When the gravitational field of a planet is strong enough, it gets enveloped by a packet or layer of gases that surround it completely. This layer is known as the atmosphere of that planet. Without an atmosphere, it will be impossible for a planet to be habitable. The temperatures would go up to boiling levels during the day and it would become icy cold during the night.

Layers of Atmosphere

The pressure and density of air decrease as we go upwards. However, the temperature of the air is more complicated to describe. In general, it decreases as we go upwards, but it may also remain constant in some areas. Depending on this and various factors, scientists have classified the atmosphere into various layers. Let us discuss them one by one

Troposphere

The troposphere is the lowest layer of air, which extends to about 12 km from the earth’s surface, though its height varies. For example, near the poles, it’s only about 9 km high, while it can go up to 17 km near the equatorial regions.

This is the densest part of the earth’s atmosphere and in fact, contains almost 80% of all the mass that is present in our atmosphere. Further, almost all the water vapors are present in the troposphere only, and thus, all-weather phenomena take place here.

Stratosphere

Above the troposphere lies the stratosphere, which extends from about 12 km to 55 km. At this height, air pressure drops down significantly and near the top of this layer, it’s only about one-thousandth times that of the sea level pressure.

Jet-powered aircraft can penetrate into the stratosphere, but no weather phenomena occur here since the conditions in this layer are highly stable. Interestingly, since the ozone layer, which absorbs UV radiation from the sun, sits inside the stratosphere, the temperature at the top of this layer is much higher $\mathrm{(0^\circ C)}$ than at the bottom $\mathrm{(-60^\circ C)}$ due to UV absorption.

Mesosphere

From approximately 50 km to 80-85 km lies the mesosphere, which is the coldest place on Earth with an average temperature of $\mathrm{(-85^\circ C)}$. The mesosphere is so high above the surface of Earth that even jet-powered aircraft cannot reach it.

While no weather phenomena occur here, the mesosphere does have some sort of clouds in the form of ice particles. This happens since there are very minute and trace amounts of water vapor in this layer that condense due to the extremely low temperatures.

When meteors reach the Earth and enter the atmosphere, they start burning up in the mesosphere and do not penetrate into the stratosphere. However, very large meteors can make it to the surface, which is what leads to the presence of meteorites on Earth.

Thermosphere

The thermosphere is the layer that starts above the mesosphere and reaches almost a thousand kilometres above the Earth. There are no water vapors or clouds in this layer, but phenomena like the Northern Lights take place here. Also, remember that the International Space Station and various other satellites orbit Earth in this layer only. One very interesting fact you should know about the thermosphere is that even though its temperature is around $\mathrm{(1500^\circ C)}$, it would not feel hot to you. This occurs due to the extremely low density of air in this region.

Another interesting phenomenon is the variation in height of the thermosphere. It is so high above the earth that it is affected by solar activity and thus, the upper part of the thermosphere is quoted to lie between 500 and 1000 km.

Exosphere

The exosphere is where the atmosphere of the earth ends. It is the uppermost layer and extends to around 10,000 km. At such enormous distances from the surface, solar winds are present and the exosphere merges into them.

Various artificial satellites orbit the Earth in this region as well. The density in this layer is so infinitesimal that most molecules here could travel for thousands of kilometers and not suffer a single collision. In fact, the exosphere does not behave like a gas since the molecules of gases that are present in this region often escape into space.

Ionosphere

The ionosphere isn’t a single defined layer of the atmosphere. Instead, the term is used to refer to the part of the atmosphere which gets ionized due to solar radiation. It includes parts of the top-three layers of Earth and extends from 50 to 1,000 km during the day. At night, the mesosphere doesn’t remain ionized and thus, is technically no longer a part of the ionosphere.

You should remember that the ionosphere is one of the most essential parts of the atmosphere when it comes to radio communications. Radio frequencies get reflected by the ionosphere and thus, without this layer, we wouldn’t be able to receive radio signals across the globe.

Composition of Atmosphere – Gases in the Atmosphere

The atmosphere of earth is composed of a large number of gases, chief among which are Oxygen, Carbon dioxide, Nitrogen, Argon, and various other gases. Nitrogen is the most prevalent and makes up about 78.08% of our air. Oxygen makes up 20.95% of our air, while argon and carbon dioxides are about 0.93% and 0.04% of the atmosphere. Water vapors are also present in the atmosphere, though the majority of them are concentrated near the sea level. Furthermore, the ionosphere contains electrons and various charged atoms and molecules.

Conclusion

The term atmosphere refers to an envelope of gases around a planet. The atmosphere of Earth is often simply called air and serves a major role in making life on this planet possible. Air pressure and density drop as we go up in the atmosphere. The atmosphere of Earth is divided into various layers. These include from bottom to top, the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Of these, the thermosphere is the coldest while the troposphere is the densest. The ionized portion of the atmosphere is called the ionosphere and includes portions of the top three layers. In terms of composition, the atmosphere comprises Nitrogen, Argon, Carbon dioxide, and most importantly, Oxygen. Water vapors are also present but are mainly concentrated near the sea level.

FAQs

1. Where do the atmosphere end and outer space start?

There is no specifically defined boundary of the Earth’s atmosphere. However, the Karman line at 100 km is usually taken as the boundary.

2. Why is the atmosphere denser near the surface?

Gravity is the primary reason for higher density at the bottom than at the top.

3. Where do commercial airplanes fly in the atmosphere?

Commercial aviation activity takes place in the stratosphere.

4. Where is the ozone layer situated?

In the stratosphere at a height of 10 to 15 km lies the ozone layer. It shields us from dangerous UV radiation and without it, our survival would be impossible.

5. What other gases besides N₂, O₂, CO₂, etc. are present in the air?

Helium, Methane, Neon, Ozone, and Nitrous oxide are also present in the atmosphere.