Some people are surprised to learn that oxygen isn’t the most abundant gas in Earth’s atmosphere composition.
Based on the relative volumes of the gases in Earth’s atmosphere, nitrogen is actually more than 3 times more than oxygen.
From largest to smallest, Earth’s atmosphere composition contains nitrogen, oxygen, argon, CO2 and trace gases. Because water vapor is highly variable geographically, it’s excluded from this total.
1. Nitrogen (78.1%)
While nitrogen is the most abundant gas in Earth’s atmosphere, it only makes up 0.005% of Earth’s crust in weight (David Darling).
Nitrogen is incredibly stable and requires a lot of energy to change forms.
Even though its volume in Earth’s crust is relatively small, nitrogen plays an important role in the nitrogen cycle.
As part of this cycle, nitrogen constantly exchange between the atmosphere and living organisms.
2. Oxygen (20.9%)
Earth has the conditions for life to flourish. Oxygen is essential to human life as our lungs respire oxygen and uses it in metabolism.
While nitrogen is an extremely stable gas, it’s difficult to break up and use for chemical processes. But oxygen will readily take part in chemical reactions because it’s an electron thief.
So even though nitrogen is plentiful, we need oxygen to drive chemical reactions that produces energy.
3. Argon (0.93%)
As an inert gas, argon doesn’t bond or do much in the atmosphere.
This is why there’s no argon cycle. But we have a nitrogen and carbon because of their abilities to bond with other elements.
When potassium radioactively decays, argon is one of the possible product. And the lithosphere has lots of potassium.
It’s not too exciting of a gas. But it’s up in the atmosphere at 0.93% of air volume.
4. Carbon Dioxide (0.04%)
Carbon is the most important element for building the molecules essential for living things.
As you can see from the long-term carbon cycle, carbon takes up various forms such as carbon dioxide (CO2), methane (CH4) and glucose (C6H12O6).
Since 1900, carbon dioxide has increased mostly because of human activity. After extracting fossil fuels, humans burn fossil fuels.
In turn, gases like methane and carbon dioxide become air pollution in the atmosphere. In fact, carbon dioxide has nearly doubled since 1900.
5. Trace Gases
The remaining portion of the atmosphere belongs to trace gases. For example, neon, helium, methane, methane and krypton are some of the major trace gases that make up a small part of the atmosphere.
But humans can also cause some trace gases. For example, chlorofluorocarbons (CFCs) has damaged the ozone layer in the north and south pole.
When chlorine enters the troposphere and eventually the stratosphere, it reacts with ozone (O3) essentially depleting it. Similar to ozone, water vapor is a variable gas.
6. Water Vapor (Variable)
Water vapor has been removed from the 100% total because of its region variability. But in can make up large portions of the atmosphere. For example, it can make up 5% by volume in hot regions but much less in colder regions.
Water vapor regulates air temperature because it absorbs solar radiation. It evaporates from lakes and rivers from the surface of Earth. Once it’s in the atmosphere, water vapor condenses such as in the form of rain. It simply changes form from water vapor to a liquid.
As part of the hydrological cycle, water is always in motion. And it’s all driven by the sun’s energy.
What is the distribution of gases in the atmosphere?
In this video, it displays a year in the life of Earth’s carbon dioxide. As you can see, carbon dioxide is the most important gas affected by human activity.
In the northern hemisphere, we see the highest concentrations of carbon dioxide from major emission sources. For example, carbon emissions are mostly focused around North America, Europe and Asia. But the gas disperses, finding its circulation path with global weather patterns and ocean currents.
Even the seasonal patterns on Earth affect the amount of carbon dioxide in the atmosphere. During photosynthesis in spring and summer, plants absorb a substantial amount of carbon dioxide from the atmosphere.
As summer transitions to fall, photosynthesis begins to decrease as carbon dioxide accumulates back into the atmosphere. This effect is from the Earth metabolism or net primary productivity.