Atmosphere of Earth

The air is all around us. It wraps the Earth like a blanket. This blanket keeps us warm. It also keeps us safe.

The air shields us from space. It stops many rocks from hitting us. It also blocks bad light from the sun. The air has many parts. Most of it is a gas called nitrogen. Some of it is the air we breathe. This air helps life grow and live.

The air is very important to us.

Earth is wrapped in a layer of gas. We call this the atmosphere. Gravity holds this air close to our planet. It acts like a shield. It blocks many meteoroids from hitting the surface. It also blocks bad light from the sun. This light is called ultraviolet radiation. The atmosphere also keeps our world warm. It does this through the greenhouse effect. This is a way the air holds in heat.

Dry air is made of different gases. Most of it is nitrogen. About 21% is oxygen, which we breathe. The rest is mostly argon. Small amounts of carbon dioxide and other gases are also there.

The atmosphere has five main layers. The lowest layer is the troposphere. This is where we live and where weather happens.

Above that is the stratosphere. It has an ozone layer. This layer helps block solar radiation. Next is the mesosphere. It is the coldest part of the air. Most meteors burn up here. Above that is the thermosphere. The International Space Station orbits here. The last layer is the exosphere. It is the very edge of space.

Earth is wrapped in a thick layer of mixed gases called the atmosphere. This layer stays close to the planet because of gravity. It acts like a protective buffer between our world and outer space. The atmosphere shields the surface from many meteoroids. It also blocks most ultraviolet solar radiation from the sun. This gas layer also helps keep our planet warm. It does this through the greenhouse effect, which is a way the air holds in heat.

To understand what air is made of, we look at its different gases. Dry air is mostly made of nitrogen, which makes up 78.08% of the mix. Oxygen is the next biggest part at 20.95%. Argon makes up 0.93% of the air. There is also 0.04% carbon dioxide and other tiny amounts of trace gases.

Air also contains water vapor. On average, water vapor is about 1% at sea level. It makes up about 0.4% of the entire atmosphere. This water vapor is a greenhouse gas that helps hold heat.

The atmosphere is not the same all the way up. It is divided into five main layers based on temperature and what is in them. The lowest layer is the troposphere, where we live and where weather happens.

Above that is the stratosphere, which contains the ozone layer. The mesosphere is the third layer and is the coldest place on Earth. The thermosphere is the fourth layer, and this is where the International Space Station orbits.

The very last layer is the exosphere, which is the edge of space.

Scientists study these layers and how they work. This field of study is called atmospheric science. People who study the history of the atmosphere use a special name: paleoclimatology.

Early pioneers in this field included Léon Teisserenc de Bort and Richard Assmann. They helped us understand how the air changes as you go higher. The atmosphere has a huge mass of about 5.15×10^18 kg. Most of this mass, about three quarters, is within 11 km of the surface.

You can see how the atmosphere works by looking at the sky. In the mesosphere, most meteors burn up when they hit the air.

In the thermosphere, you might see the beautiful colors of the aurora. The exosphere is so thin that atoms can travel far without hitting each other. Even though the air gets thinner as you go up, there is no definite line where the atmosphere ends. We often use the Kármán line at 100 km to mark the edge of space.

Earth is surrounded by a massive layer of mixed gases known as the atmosphere. This layer is held in place by gravity, preventing it from drifting into space. The atmosphere serves as a vital protective buffer for our planet. It shields the surface from many meteoroids and blocks most harmful ultraviolet solar radiation. Additionally, it regulates our climate by reducing diurnal temperature variation, which is the difference between day and night temperatures. Through the greenhouse effect, the atmosphere retains heat to keep the planet warm.

To understand the atmosphere, we must look at its chemical composition. Dry air is composed of several specific gases by mole fraction. Nitrogen is the most abundant, making up 78.08% of the mix. Oxygen follows at 20.95%, while argon accounts for 0.93%. Carbon dioxide makes up 0.04%, along with various other trace gases.

Water vapor is also present, though its concentration varies. It averages about 1% at sea level and 0.4% throughout the entire atmosphere. Water vapor is a significant greenhouse gas that helps manage Earth's temperature.

Scientists categorize the atmosphere into five distinct layers based on temperature and composition. These layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

The troposphere is the lowest layer, extending from the surface to about 12 km. This is where terrestrial plants perform photosynthesis and animals carry out respiration. Above this lies the stratosphere, which reaches up to 55 km. The stratosphere contains the ozone layer, which absorbs ultraviolet radiation. This absorption causes temperatures to rise with altitude in this specific layer.

The mesosphere sits above the stratosphere, ranging from 50 km to about 85 km. This layer is characterized by dropping temperatures as altitude increases. In fact, the mesopause is the coldest place on Earth, with average temperatures around −85 °C. The mesosphere is also where most meteors burn up upon entry.

Above the mesosphere is the thermosphere, extending from 80 km to roughly 1,000 km. In this layer, temperatures can rise as high as 1500 °C due to solar X-ray absorption. The International Space Station orbits within this layer.

The outermost layer is the exosphere, which extends from the thermopause to about 10,000 km. In this region, the air is so thin that particles rarely collide. Instead, they follow ballistic trajectories and can escape into space. Every second, Earth loses approximately 3 kg of hydrogen and 50 g of helium to space. While the exosphere is extremely tenuous, it contains many artificial satellites. The Kármán line at 100 km is often used as the conventional boundary for space.

Atmospheric processes have changed significantly throughout Earth's history. The primordial atmosphere was formed from gases accreted from the solar nebula. Over time, volcanism, outgassing, and the evolution of life changed its makeup. Specifically, photoautotrophs played a role in these shifts. Today, human activities like deforestation and fossil-fuel use contribute to climate change. These activities also lead to ozone depletion and acid deposition. Understanding these changes is a major part of atmospheric science, which includes subfields like climatology.

Researchers use various methods to study these complex systems. The study of the historic atmosphere is known as paleoclimatology. Early pioneers such as Léon Teisserenc de Bort and Richard Assmann helped establish the field. The total mass of the atmosphere is approximately 5.15×10^18 kg. Interestingly, three quarters of this massive weight is concentrated within the first 11 km of the surface. This concentration explains why air pressure and density decrease so rapidly as you climb higher.