Question

What two gases compose most of Earth's atmosphere?

Short answer

Nitrogen and Oxygen.

Step-by-step solution

Identifying Major Atmospheric Gases

The Earth's atmosphere is made up of various gases. The two gases that are most abundant are nitrogen and oxygen. Together, they make up about 99% of the atmosphere's composition.

Recognizing Nitrogen's Role

Nitrogen (N₂) is the most abundant gas in the atmosphere. It constitutes approximately 78% of the Earth's atmosphere. It plays a crucial role in various biological processes, such as the nitrogen cycle, which is essential for plant growth.

Recognizing Oxygen's Role

Oxygen (O₂) is the second most abundant gas and makes up about 21% of the atmosphere. It is essential for respiration in humans and animals and also plays a significant role in combustion and numerous chemical reactions on Earth.

Key concepts

Nitrogen

Nitrogen is the most prevalent gas in Earth's atmosphere, accounting for approximately 78% of its composition. This inert gas is stable and non-reactive under normal atmospheric conditions. It plays a fundamental role in the survival and functioning of ecosystems.

One might wonder why nitrogen is so crucial. Well, despite its abundance, only specific processes can utilize atmospheric nitrogen for biological functions. Primarily, it is essential in the creation of amino acids, nucleic acids, and proteins, vital compounds for life. Nitrogen itself is not directly usable by plants or animals until it undergoes certain conversions.

These conversions are part of the nitrogen cycle, which we'll discuss further. In scientific terms, nitrogen has a diatomic molecular structure, represented as N₂. This structure accounts for its stability, as the triple bond between the nitrogen atoms is extremely strong.

For life to take full advantage of nitrogen, it must first be `fixed` or converted into a more usable form by processes like fixation by bacteria or industrial methods like the Haber process.

Oxygen

Oxygen, making up about 21% of Earth's atmosphere, is the second most abundant gas. Unlike nitrogen, oxygen is highly reactive and is crucial for many essential processes.

Without oxygen, the process of respiration in humans and animals wouldn't be possible. In simple terms, oxygen serves as the key component that is inhaled, allowing our cells to release energy from food. This process, termed cellular respiration, keeps us and other living organisms alive.

Apart from sustaining life, oxygen also plays a role in combustion. It is the reason why things burn. For a fire to ignite, it needs three things: heat, fuel, and oxygen, which sustains the chemical reaction of burning.

On a molecular level, oxygen exists primarily as O₂ and has a diatomic molecular structure. It is also present in the ozone layer as O₃, providing a shield that protects Earth from harmful ultraviolet rays.

Thus, oxygen’s role extends beyond just breathing; it is a critical component that supports multiple natural processes.

Nitrogen Cycle

The nitrogen cycle is an intricate system that converts nitrogen from one form to another. It is vital for converting inert atmospheric nitrogen into a form usable by living organisms.

The cycle begins with nitrogen fixation, a process where specialized bacteria convert N₂ into ammonia (NH₃) or related compounds. Plants can then assimilate these compounds, which become part of the plant's biological structures.

The Steps of the Nitrogen Cycle:

• Nitrogen Fixation: Carried out by bacteria, either free-living in soil or in symbiotic relationships with plant roots.
• Nitrification: The conversion of ammonia to nitrate ions (NO₃⁻) by nitrifying bacteria, making nitrogen accessible to plants.
• Assimilation: Plants absorb nitrates and convert them into essential organic molecules like proteins.
• Ammonification: When plants and animals die, decomposers break down organic matter, returning nitrogen to the soil as ammonia.
• Denitrification: Some bacteria can convert nitrates back to N₂, releasing it to the atmosphere and completing the cycle.

In this way, nitrogen cycles through the environment, maintaining the balance necessary for life on Earth. Without it, the ecosystem's functionality would drastically diminish.