The term "atmosphere" is derived from the Greek words "atmos," meaning "breath," and "sphaira," meaning "sphere." Scientifically, the atmosphere can be defined as a layer of gases that surrounds the Earth. This gaseous sphere, which supports life on Earth, stays attached to the planet due to gravity and is an essential part of various natural processes.

The overall thickness of the atmosphere exceeds 1,000 km, but its effective thickness is generally considered to be around 190-200 km. The composition of the atmosphere consists of 78% nitrogen, 21% oxygen, and less than 1% of other gases (such as argon, carbon dioxide, neon, etc.). Additionally, up to 4% of the atmosphere can contain water vapor and dust particles.

The atmosphere possesses various characteristics that support life and protect the Earth. It blocks harmful ultraviolet rays from the Sun, provides protection from meteors and other space objects, and maintains the Earth’s heat balance, creating a suitable environment for life.

Layers of the Atmosphere

The atmosphere is divided into different layers based on its characteristics. Each of these layers plays different roles and has diverse impacts on life. The atmosphere is particularly divided into layers based on its gas composition, chemical and physical properties, and temperature.

^{Layers of the Atmosphere (Source: Freepik / brgfx)}

Troposphere

The troposphere is the first layer, surrounding the Earth's surface and containing about 75% of the atmosphere's total mass. This is where most of the weather events that create conditions suitable for life occur. It is the layer closest to the Earth's surface and gets its name from the Greek word "tropos," meaning "change," because of the constantly changing weather patterns and mixing of gases.

The thickness of the troposphere varies by region. At the equator, it extends up to about 16-17 kilometers, while at the poles, it is around 6-7 kilometers thick. Generally, the troposphere has a thickness between 8 and 14 kilometers, with the thinnest parts being at the poles. As altitude increases, the temperature in the troposphere decreases, which helps create an environment conducive to life.

This layer contains the air we breathe, clouds, and weather events. It is the densest layer, holding three-fourths of the entire atmosphere’s mass. The air in the troposphere is made up of 78% nitrogen and 21% oxygen, with the remaining 1% consisting of gases like argon, water vapor, and carbon dioxide.

The troposphere is the layer we commonly experience in our daily lives. The wind we feel on our faces, the clouds we see in the sky, and the birds flying are all effects of this layer. The troposphere is the most dynamic and vital part of the atmosphere, supporting life on Earth.

Tropopause

The tropopause is the boundary layer at the top of the troposphere, separating it from the stratosphere. The temperature remains constant at this layer, which is about 1-2 kilometers thick. The height of the tropopause is about 16-17 kilometers at the equator and 6-7 kilometers at the poles. The tropopause represents the region where most meteorological events end and a calmer structure begins.

Stratosphere

Located above the troposphere and below the mesosphere, the stratosphere is the second layer of the atmosphere, extending up to 50 kilometers in height. It gets its name from the Latin word "strat," meaning "layer," and has its own sublayers. The stratosphere is 35 kilometers thick and contains the ozone layer, which plays a critical role in absorbing harmful ultraviolet (UV) rays from the Sun and protecting the Earth's surface.

Without the ozone layer, harmful UV rays would reach the Earth's surface and cause significant damage to living organisms. In the stratosphere, the temperature increases with altitude, which is an important characteristic that distinguishes it from other atmospheric layers.

The air in the stratosphere is more stable than in the troposphere. Unlike in the troposphere, there are no factors like turbulence or storms to mix the air. As a result, the lower part of the stratosphere contains cold, dense air, while the upper part is warmer and lighter. This temperature pattern is the opposite of what we experience in the troposphere. For example, if you were to climb a mountain in the stratosphere, you would have to remove your thick clothing as you neared the peak.

Due to its stable weather conditions and increasing temperatures, the stratosphere is a region often preferred by some aircraft for their flight paths. With its properties, the stratosphere is not only a protective layer of the atmosphere vital to life on Earth but also an important area for scientific and air travel purposes.

^{Layers of the Atmosphere (Source: Coolgeography.co.uk)}

Stratopause

The stratopause is located at the top of the stratosphere, forming the boundary between the stratosphere and the mesosphere. At this layer, the temperature becomes stable and typically hovers around 0°C. This region represents a more stable and less active area of the atmosphere.

Mesosphere

The mesosphere is the third layer of the atmosphere, located above the stratosphere and below the thermosphere. It extends from about 50 kilometers to 80-90 kilometers and is 35 kilometers thick. The word "meso" means "middle," and the mesosphere is known as the middle layer of the atmosphere.

The most notable characteristic of this layer is the rapid decrease in temperature with altitude. Temperatures in the mesosphere can drop to as low as -90°C. The air is so thin in this layer that it is impossible to breathe. However, the mesosphere contains more gas than the thermosphere, and these gases cause meteors entering the atmosphere to burn up as they collide with the air. Therefore, the mesosphere is also known as the "burning layer of meteors."

When we observe meteor showers, the streaks of light we see in the sky are caused by meteors burning up due to friction in the mesosphere. While the air in the exosphere and thermosphere is too sparse for meteors to burn, the gases in the mesosphere are dense enough to create friction and cause meteors to disintegrate.

As the coldest layer of the atmosphere, the mesosphere also holds significant importance in natural phenomena like meteor showers.

Mesopause

The mesopause is the boundary between the mesosphere and the thermosphere, where temperatures are the lowest, reaching around -90°C. This region is considered the coldest part of the atmosphere.

Thermosphere

The thermosphere lies above the mesosphere and below the exosphere, extending from about 90 kilometers up to 400-500 kilometers in height. The "thermo" prefix refers to "heat," and the thermosphere's most notable feature is the rapid increase in temperature with altitude. Temperatures in this layer can reach 1,500°C, or even up to 2,000°C in some cases.

However, despite these high temperatures, the thermosphere’s air density is so low that you wouldn’t feel the heat. Since there are not enough gas molecules to transmit heat, an object or person in this layer would still feel cold. The sparse gas molecules also make it impossible for sound waves to propagate.

The thermosphere also includes the ionosphere, which is critical for the transmission of radio waves. The ionized gases in the thermosphere reflect radio signals back to the Earth's surface, playing a vital role in communication. Additionally, the thermosphere hosts satellites like the International Space Station (ISS) in low Earth orbit.

The thermosphere is much thicker than the inner layers of the atmosphere but does not cover as large an area as the exosphere. This layer is crucial for both space research and communication technologies.

Ionosphere

The ionosphere is a layer that starts around 60 kilometers above the Earth’s surface and extends up to 1,100 kilometers. It consists of ionized gases created by sunlight. Overlapping the mesosphere, thermosphere, and exosphere, the ionosphere is a highly active part of the atmosphere, named after the electrically charged particles (ions) formed by solar radiation.

Solar radiation determines the dynamics of the ionosphere. During the day, molecules become ionized, increasing electron density, while at night, electrons and ions recombine, reducing this density. The ionosphere’s electron density is also influenced by seasonal changes, Earth’s position around the Sun, and the Sun’s 11-year cycle.

The ionosphere is essential for radio wave propagation. It reflects radio signals, enabling long-distance communication in both civil and military shortwave communication. However, satellite signals can be disrupted as they pass through the ionosphere, requiring correction. The ionosphere is divided into D, E, F1, and F2 layers based on ionization density. The F layer, located above 150 kilometers, is the region with the highest ionization, supporting global communication for shortwave radio.

Solar events like solar flares can affect the ionosphere’s structure, causing communication interruptions. It is also the region where auroras (the Northern and Southern Lights) occur due to interactions between high-energy particles from the Sun and the Earth’s atmosphere.

Exosphere

The exosphere is the outermost layer of the Earth’s atmosphere, extending from about 500 kilometers up to 10,000 kilometers in height. The word "exosphere" means "outer," and this layer marks the boundary between the Earth’s atmosphere and space. It is the largest and least dense layer, primarily composed of light gases like hydrogen and helium.

Due to the vast distances between gas molecules, it is impossible to breathe in the exosphere, and it feels extremely cold. The exosphere is also where gravity’s influence weakens significantly and where space begins. This layer serves as a transition zone between Earth’s atmosphere and the vacuum of space.

The exosphere is where artificial satellites and other space vehicles orbit the Earth. Its wide expanse shows how far you need to travel from the Earth’s surface to reach space. This layer is the gate to outer space, where Earth's atmosphere is very thin and peaceful, and it opens into the vast emptiness of space.

Vital Functions of the Atmosphere

• Respiration and Life Support: The atmosphere contains oxygen, the essential gas for respiration, enabling life to thrive.
• Heat Balance Maintenance: It regulates the amount of sunlight reaching the Earth, preventing excessive heating or cooling.
• Protection: It shields the Earth from harmful ultraviolet rays and protects against meteor impacts.
• Water Cycle: By holding water vapor, the atmosphere contributes to precipitation and helps maintain the climate balance.