Composition of the Atmosphere (Leaving Cert Geography): Revision Notes
Composition of the atmosphere
What is the atmosphere?
The atmosphere is a mixture of gases that surrounds our planet Earth. This gaseous envelope provides the air we breathe and plays an essential role in supporting life on Earth. Understanding what makes up our atmosphere is crucial for understanding climate patterns, weather systems, and environmental changes happening on our planet.
The atmosphere's composition directly influences global temperatures, rainfall patterns, and sea level changes. Scientists study atmospheric composition because greenhouse gas levels are rising, which climate models predict could increase Earth's average temperature by around 4°C this century if current trends continue.
Climate scientists use sophisticated computer models to predict future atmospheric changes. These models combine data about current gas concentrations with emissions projections to forecast potential climate scenarios over the coming decades.
Major atmospheric gases
Nitrogen ()
Nitrogen is by far the most abundant gas in our atmosphere, making up approximately 78% of the total volume. This gas is vital for all living things and participates in important natural cycles. Nitrogen plays a key role in biological processes, particularly through nitrogen fixation. During this process, bacteria convert atmospheric nitrogen into forms that plants can absorb and use for growth. Without this natural process, plants would struggle to obtain the nitrogen they need to produce proteins and other essential compounds.
Nitrogen Fixation Process:
Step 1: Atmospheric nitrogen () is chemically inert and cannot be used directly by plants
Step 2: Specialised bacteria (like Rhizobium in root nodules) convert into ammonia ()
Step 3: Ammonia is further converted to nitrates () that plants can absorb through their roots
Step 4: Plants use these nitrogen compounds to build proteins and DNA
Oxygen ()
Oxygen comprises about 21% of the atmosphere's volume. This gas is absolutely essential for respiration in both plants and animals, including humans. Every time we breathe in, we extract oxygen from the air to power cellular processes in our bodies. Plants also require oxygen for respiration, though they produce it during photosynthesis as well. The oxygen in our atmosphere has built up over billions of years, primarily through photosynthesis by plants and marine organisms.
Argon ()
Argon represents approximately 0.93% of atmospheric volume. This noble gas is chemically inert, meaning it doesn't react with other substances under normal conditions. Argon remains relatively constant in its atmospheric concentration because it doesn't participate in chemical reactions or biological processes. Its presence demonstrates that not all atmospheric gases are actively involved in supporting life processes.
Carbon dioxide ()
Though carbon dioxide makes up only about 0.04% of the atmosphere, it plays a disproportionately important role as a greenhouse gas. Carbon dioxide concentrations have been steadily increasing due to human activities such as burning fossil fuels and deforestation. This increase is contributing significantly to global warming because carbon dioxide traps heat in the atmosphere, preventing it from escaping back to space.
Despite its small percentage, has increased by over 40% since pre-industrial times. This seemingly small change has major climate implications because greenhouse gases are extremely effective at trapping heat, even in low concentrations.
Trace gases
The remaining gases in the atmosphere include various trace gases present in very small quantities. These include neon, helium, methane, and krypton. While their individual percentages are tiny, some trace gases can have significant impacts on climate and atmospheric chemistry. For example, methane is another important greenhouse gas that, despite its low concentration, contributes to global warming.
How atmospheric composition varies
The composition of our atmosphere isn't exactly the same everywhere on Earth. At higher altitudes, the proportion of oxygen decreases significantly, which is why mountaineers and aircraft passengers may experience difficulty breathing. This reduction in oxygen concentration makes it physically harder for our bodies to extract the oxygen they need from each breath.
Location also affects atmospheric composition. Industrial areas may have higher concentrations of pollutants, while remote oceanic regions typically have cleaner air with fewer human-made gases.
The decrease in oxygen at altitude follows an exponential pattern. At 3,000 metres above sea level, oxygen concentration is about 68% of sea level values, which is why many people experience altitude sickness when travelling to high mountain regions.
Why atmospheric composition matters
Understanding atmospheric composition is vital for several important environmental processes. The atmosphere controls weather patterns by influencing how heat and moisture move around the planet. Different gases absorb and reflect solar radiation in various ways, affecting global temperature patterns.
The greenhouse effect depends directly on atmospheric composition. Greenhouse gases like carbon dioxide and methane trap heat that would otherwise escape to space, keeping Earth warm enough to support life. However, increasing concentrations of these gases are enhancing this natural greenhouse effect, leading to global warming.
The atmosphere also serves as Earth's protective shield, filtering out harmful solar radiation that could damage living organisms. Without our atmospheric envelope, Earth would be bombarded by dangerous cosmic radiation and experience extreme temperature swings.
The natural greenhouse effect is essential for life - without it, Earth's average temperature would be about -18°C instead of the current +15°C. The problem is not the greenhouse effect itself, but the enhancement of this effect due to increasing greenhouse gas concentrations.
Key Points to Remember:
- Nitrogen (78%) and oxygen (21%) make up 99% of the atmosphere, with argon and carbon dioxide as the next most abundant gases
- Each atmospheric gas serves specific functions - nitrogen for biological processes, oxygen for respiration, and carbon dioxide as a key greenhouse gas
- Atmospheric composition varies with altitude and location, with oxygen decreasing at higher elevations
- The atmosphere regulates Earth's climate through the greenhouse effect and protects us from harmful solar radiation
- Understanding atmospheric composition is essential for addressing climate change and environmental protection