Composition of the Atmosphere
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The atmosphere is the gaseous envelope that surrounds the Earth. Though it extends several hundred kilometers above the planet’s surface, it is quite thin when compared to the size of the Earth itself. Most of the atmospheric mass is concentrated within the first few kilometers due to the force of gravity pulling the gases downward.
Air is a mixture of different gases. According to the Earth Science Reference Tables (page 11), the two most abundant gases in the atmosphere are nitrogen and oxygen. Nitrogen makes up approximately 78% of the air by volume, while oxygen accounts for about 21%. The remaining 1% is made up of trace gases such as argon, carbon dioxide, neon, and water vapor. Although water vapor comprises a small fraction of the atmosphere by volume, it plays a critical role in weather and climate processes.
When referring to the atmosphere’s composition, the data in the Reference Tables focuses specifically on the Troposphere, which is the lowest layer of the atmosphere and the one where we live. This layer contains almost all of the air’s mass and is where all weather occurs.
Layers of the Atmosphere
The atmosphere is divided into layers based on how temperature changes with altitude. These changes are not linear, and the temperature trend reverses several times as you move upward. The layers, in order from the surface upward, are the Troposphere, Stratosphere, Mesosphere, and Thermosphere.
Troposphere: This is the lowest layer, extending from Earth’s surface to an average height of about 12 km (varies by location and season). In this layer, temperature decreases steadily with altitude. The Troposphere contains nearly all the atmosphere’s water vapor and is the zone where weather systems such as clouds, rain, and storms form. The upper boundary is called the Tropopause.
Stratosphere: Above the Tropopause is the Stratosphere, which extends to around 50 km. Unlike the Troposphere, temperatures here increase with altitude. This warming trend is due to the presence of the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun. The top of this layer is known as the Stratopause.
Mesosphere: This layer extends from about 50 km to 85 km. Here, the temperature again decreases with altitude. The Mesosphere is the coldest layer of the atmosphere. The top of this layer is the Mesopause.
Thermosphere: Beyond the Mesopause lies the Thermosphere. In this outer layer, temperatures rise dramatically with altitude, often reaching 1,000°C or more. Despite these high temperatures, it would not feel hot to humans because the air is so thin. There is no defined boundary at the top; the Thermosphere gradually merges into the vacuum of outer space.
Other Atmospheric Properties
When examining the right-hand side of the atmospheric chart on page 14 of the Reference Tables, we see two additional properties of the atmosphere: atmospheric pressure and water vapor concentration.
Atmospheric Pressure: Pressure decreases rapidly with altitude. This is because most of the atmospheric mass is concentrated near the Earth’s surface, held by gravity. For this reason, the air is much denser and exerts more pressure at sea level than at higher altitudes.
Water Vapor: Water vapor is found almost entirely within the Troposphere. This is why all weather phenomena — clouds, precipitation, storms — are restricted to this layer. The higher you go, the less water vapor is present, which explains why precipitation and cloud formation are rare in higher layers of the atmosphere.
Understanding the structure and properties of the atmosphere is critical not only for meteorology and climate science, but also for aviation, astronomy, and environmental studies. The layers of the atmosphere influence everything from the temperature at your feet to the satellite communications above your head.
Timeline of Major Discoveries and Developments Related to the Atmosphere
~350 BCE – Aristotle proposes early theories about air and weather. Greek philosopher Aristotle wrote Meteorologica, one of the first attempts to describe atmospheric phenomena, including wind, clouds, and weather.
1643 – Torricelli invents the barometer. Evangelista Torricelli created the mercury barometer, proving that air has weight and pressure. This was a foundational moment in atmospheric science.
1700s–1800s – Discovery of atmospheric gases. Chemists such as Joseph Priestley and Antoine Lavoisier identified major atmospheric gases, including oxygen and nitrogen.
1899 – Stratosphere is discovered. Léon Teisserenc de Bort used weather balloons to discover that temperature increases above a certain altitude, leading to the identification of the stratosphere.
1920s – Ozone layer is identified. The presence of the ozone layer in the stratosphere was confirmed, helping explain the absorption of ultraviolet radiation.
1950s–1960s – Development of weather satellites. Satellites such as TIROS-1 (1960) provided the first images of Earth’s atmosphere, revolutionizing meteorology and global climate monitoring.
1985 – Discovery of the ozone hole. Scientists detected a significant thinning of the ozone layer over Antarctica, prompting global action and the eventual Montreal Protocol.
Present Day – Continued research on climate change, greenhouse gases, and atmospheric dynamics Modern science uses satellites, weather stations, and computer models to track atmospheric changes related to global warming, storms, and air quality.
Frequently Asked Questions
What are the main gases in Earth’s atmosphere?
Nitrogen (78%) and oxygen (21%) are the two most abundant gases in Earth’s atmosphere. Argon, carbon dioxide, and water vapor make up most of the remaining 1%.
What is the troposphere and why is it important?
The troposphere is the lowest layer of the atmosphere where all weather occurs. It contains most of the air’s mass and nearly all of the atmospheric water vapor.
Why does temperature increase in the stratosphere?
The temperature increases in the stratosphere due to the ozone layer, which absorbs ultraviolet radiation from the Sun and converts it into heat.
What causes air pressure to decrease with altitude?
Air pressure decreases with altitude because the atmosphere becomes less dense as you move away from Earth’s surface, and gravity pulls most air molecules close to the ground.
Where does weather occur in the atmosphere?
All weather events, including clouds, precipitation, and storms, occur within the troposphere. This is because it is the only layer that contains significant amounts of water vapor.
How thick is the Earth’s atmosphere?
While there is no precise boundary, the atmosphere extends roughly 500 to 1,000 kilometers above Earth’s surface, gradually fading into space. Most of its mass, however, is within the first 10 to 15 kilometers.
What is the role of the ozone layer?
The ozone layer absorbs harmful ultraviolet (UV) radiation from the Sun, protecting living organisms from its damaging effects. It is located within the stratosphere.
Why is the atmosphere important for life on Earth?
The atmosphere provides essential gases for life, shields Earth from UV radiation, and moderates the planet’s temperature. It also protects us from meteoroids by burning them up upon entry.
What happens in the mesosphere?
The mesosphere is where temperatures decrease with altitude again, and it’s also the layer where most meteoroids burn up due to friction with atmospheric particles.
Is there a clear boundary between the atmosphere and space?
No, there is no definite edge. The atmosphere gradually thins out into space. The Kármán line, located at 100 kilometers above sea level, is often used to mark the boundary of outer space.