The atmosphere is the gaseous envelope that surrounds the Earth and is held to it by gravity. This vital layer not only contains the gases essential for the survival of living things, but also acts as a shield against harmful solar radiation and is fundamental to the water cycle. To learn more about the importance of the atmosphere on our planet, you can visit Earth's Atmosphere.
Since its formation approximately 4600 billion years ago , the atmosphere has undergone a series of significant changes in its composition. Initially, the atmosphere was composed mostly of carbon dioxide (CO2 ) , with little to no oxygen. It was only through the photosynthetic activity of the first living organisms that oxygen began to accumulate, eventually creating an atmosphere similar to the one we know today. To learn more about the composition of the atmosphere, see this article on atmospheric composition.
The atmosphere can be divided into horizontal layers defined by different variables, such as pressure, temperature, density, chemical composition, and electrical and magnetic molecular state . These layers are not uniform across the planet, as their thickness and characteristics can vary considerably depending on geographic location and climatic conditions. A detailed analysis of the atmospheric layers can be found in this resource.
Below is a detailed description of the main layers of the atmosphere, starting from the Earth's surface and moving out into outer space:
1. Homosphere
The homosphere extends to an altitude of approximately 80 km . In this first layer, the chemical composition of the gases is relatively uniform. Here, the ideal gas laws apply, and continuous mixing of atmospheric components is observed, resulting in variations in density and pressure at different altitudes. The homosphere is where weather phenomena develop and where most of the climatic events we experience occur. Changes in the structure of the atmosphere, including the homosphere, are essential for understanding climate, so feel free to read more in this article about temperature variation with altitude.
2. Heterosphere
Above the homosphere lies the heterosphere , which begins at an altitude of 80 km and extends into space. In this region, the chemical composition begins to vary, as lighter gases, such as helium and hydrogen, tend to settle in the upper layers, while heavier gases, such as oxygen and nitrogen, are found closer to Earth. Here, pressure and temperature decrease considerably, and the mixture of gases is less uniform. For information on phenomena in this layer, we recommend visiting this article about the atmosphere.
The heterosphere is divided into several sublayers: the nitrogen layer (up to 200 km), the atomic oxygen layer (between 200 and 1.000 km), and the helium layer (between 1.000 and 3.500 km). Gas separation occurs due to diffusion, resulting in a decrease in density with increasing altitude.
3. Troposphere
The troposphere is the layer closest to Earth's surface, varying in height from 9 to 18 km depending on location: lower at the poles and higher at the equator. This layer of air not only supports most life on Earth but also contains approximately 75% of the atmosphere's mass. In this layer, the temperature decreases with altitude, averaging a decrease of about 0.65 °C for every 100 m of altitude. For more information on how these layers work, we suggest reading this article about Earth's layers.
The troposphere is where weather phenomena such as rain, wind, and storms occur. At the top of the troposphere is the tropopause , which marks the boundary between the troposphere and the stratosphere, where the temperature remains relatively constant and convective activity is minimized. To learn more about the types of clouds that form in this layer, see this article on altocumulus clouds.
4. Stratosphere
The stratosphere extends from the tropopause, located approximately 15 km above the Earth's surface, to the stratopause at an altitude of 50 km . In this layer, the temperature begins to increase with altitude, a phenomenon due to the presence of the ozone layer . This ozone layer is crucial because it absorbs most of the sun's harmful ultraviolet radiation, thus protecting life on Earth. To learn more about the importance of this layer, visit this article about the ozone layer.
Ozone is concentrated between 20 and 30 km in altitude. The stratosphere is also where commercial airplanes fly to avoid the turbulent effects of the troposphere.
5. Mesosphere
Located between 50 and 85 km in altitude, the mesosphere is the coldest layer of the atmosphere, with temperatures that can drop to -85 °C at its highest point. It is in this layer that meteoroids disintegrate due to the high atmospheric density. Furthermore, meteor showers and other meteoroid phenomena occur in this region. To learn more about how these phenomena occur, see this article that explains the formation of cirrus clouds.
The mesopause is the term used to refer to the upper boundary of this layer.
6. Thermosphere
The thermosphere , which extends from 85 km to 600 km , experiences a significant increase in temperature, which can reach up to 1500 °C . In this layer, the ionization of gases is prominent, leading to the formation of the aurora borealis and australis. As gases are ionized, they become electrically charged particles that affect radio communications and other technological systems. To understand how temperature varies with altitude, visit [link to relevant information].
The International Space Station orbits in this layer, functioning as an international research laboratory.
7. Exosphere
The exosphere is the outermost layer of the atmosphere, extending from 600 km to 10.000 km . In this layer, gases are extremely scarce and exist in an atomic state, meaning they have a very low probability of colliding with each other. This layer contains low-Earth orbit and geostationary satellites, and it is also the region where the atmosphere begins to merge with outer space. Here, satellites move at high speeds, and the atmosphere is almost nonexistent.
The exosphere also contains the Van Allen Belts , which are regions of intense radiation where charged particles are trapped by Earth's magnetic field. For more information on how the atmospheres of other planets compare to our own, we invite you to read this article about Jupiter's atmosphere.
Impact of Climate Change on the Structure of the Atmosphere
Recent research has shown that human activity is altering the structure of the atmosphere. For example, greenhouse gases have caused the troposphere to expand and the stratosphere to contract. This phenomenon may be responsible for changes in weather patterns and the frequency of extreme weather events. For a broader perspective on the effect of greenhouse gases, you can visit this article on the conversion of greenhouse gases into rocks.
The tropopause, which separates the troposphere from the stratosphere, has risen significantly over the past few decades, suggesting that the layer of the atmosphere closest to life on Earth is thickening as global warming progresses. This thickening could lead to increased intensity of storms and other weather phenomena.
Furthermore, the thinning of the stratosphere has been correlated with changes in temperature distribution, demonstrating that climate change continues to affect the atmosphere in multiple ways, highlighting the urgent need to address greenhouse gas emissions.
The atmosphere, in its complex stratification, is not only an essential component for life on Earth, but also a vital indicator of the environmental changes we are experiencing. It is crucial that we continue to study and understand these changes to protect our planet and ensure a sustainable future.
