Atmosphere: Definition, Layers and Significance

In the entire solar system, the earth is the only planet where we see life. So one might wonder what allows life to exist, survive and flourish on the earth. To know the answer we might need to look at Life in its smallest form which is a single cell. We see that there is a thin layer of protection around the cell. The cell’s membrane or outer barrier selectively filters what goes in or out of the cell. Similarly, the earth is surrounded by a thin protective layer that protects the earth from harmful radiation from the sun and other stars. This protective layer is called the atmosphere. In this article, we will uncover interesting facts about the earth’s atmosphere and how it help life on earth to survive and flourish. So let us dive in to know more.

Introduction:

The planet earth is the only planet in the entire solar that allows life to exist. And one of the main reasons for this is that the earth is surrounded by a thin protective layer that selectively filters what goes in or out. This protective layer is called the earth’s atmosphere. So the atmosphere consists of an envelope of gasses held around the planet by gravity, that acts as the world’s biggest membrane.

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, colorless, tasteless, and formless, and blend together so well that 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 tiny percent of volume comes from minor gases like carbon dioxide. But this mostly consistent mixture starts to deviate as we get toward the outer edge of the atmosphere.

Layers of Atmosphere:

To better study the progression, we can break the atmosphere into vertical layers or spheres using several different characteristics. The four layers that we hear most about are the troposphere, stratosphere, mesosphere, and thermosphere. And these layers come from studying the atmosphere based on its temperature structure. Each layer has a different starting temperature that increases or decreases as we move toward outer space. The temperature even affects the thickness of the layers.

Troposphere:

The layer closest to the earth where all the weather and most of the air molecules exist is known as Troposphere. The Troposphere can extend anywhere from 8 to 16 km above the surface, depending on the season or latitude of where you are on the globe. This 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 is thickest where air molecules are spread out like in warm places near the equator. The majority of the mass of the entire atmosphere is contained in the troposphere, between 75 to 80%. Most of the water vapor in the atmosphere along with the dust and ash particles is present in this layer. All the helicopters, passenger flights, and hot air balloons fly in this layer.

Stratosphere:

When we move to the stratosphere, the next layer, the 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 of the atmosphere. The ozone layer allows the wavelengths conducive to life to pass through while filtering out those that are harmful, like most Ultraviolet waves. Absorbing UV rays is what causes the temperatures to increase in the stratosphere. The stratosphere extends between 16km to 50 km above the surface of the earth. Fighter jets, missiles, and supersonic jets fly in this layer.

Mesosphere:

The top of the stratosphere is called the stratopause. Above that is the mesosphere. Which reaches as far as 85 km above the earth’s surface. Temperatures decrease in the mesosphere with the altitude. In fact, the coldest temperatures in the atmosphere are near the top of the mesosphere it dropping up to -90 degrees celsius. The atmosphere is thin here but it is thick enough to burn the meteors entering the atmosphere. Burning of the meteors creates what we usually call shooting stars.

Thermosphere:

The top of the mesosphere is called mesopause. Thermosphere starts from the mesopause and extends up to around 500 km above the earth’s surface. The temperatures here increases with the altitude and they can go as high as 2000 degree Celsius.

Significance of the atmosphere:

The uppermost layer that blends with outer space is knowns as the exosphere. The pull of gravity is so small here that the molecules of gas escape into outer space. Altogether the atmosphere extends up to 600km above the earth’s surface. which seems a lot but when compared to the diameter of the earth which is 12756 km, the atmosphere seems like the peel of an orange. This thin layer of gas is so critical for life to exist. Without the atmosphere, none of the processes that we study in the hydrosphere, lithosphere, and biosphere would function. Energy from the sun is constantly passing through the different layers of the atmosphere landing on and being absorbed into the earth’s surface to provide the heat and warmth for life.

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