1. Nitrogen (N2): Makes up about 78% of the atmosphere. Nitrogen is inert and doesn't actively participate in many atmospheric processes. It's primarily a "filler" gas. However, it's crucial for life because:

* Essential for plant growth: Plants convert nitrogen from the atmosphere into usable forms through a process called nitrogen fixation.

* Part of the air we breathe: While we don't directly use nitrogen, its presence helps dilute oxygen and provides a stable environment for other gases.

2. Oxygen (O2): Makes up about 21% of the atmosphere. Oxygen is essential for life because:

* Respiration: We breathe oxygen to fuel our bodies and produce energy.

* Combustion: Oxygen is necessary for burning fuels like wood and fossil fuels.

* Ozone layer: Oxygen in the upper atmosphere forms ozone (O3), which absorbs harmful ultraviolet radiation from the sun.

3. Argon (Ar): Makes up about 0.9% of the atmosphere. Argon is a noble gas, meaning it is very unreactive. Like nitrogen, it primarily acts as a "filler" gas. However, it has some uses in:

* Lighting: Argon is used in fluorescent and incandescent light bulbs.

* Welding: It's used as a protective gas in welding processes.

These three gases make up the vast majority of the Earth's atmosphere, with trace amounts of other gases playing important roles as well.