* Nitrogen (N2): 78.084%

* Oxygen (O2): 20.946%

* Argon (Ar): 0.934%

These three gases make up over 99% of the atmosphere. Other gases present in trace amounts include:

* Carbon dioxide (CO2): 0.041% (increasing due to human activity)

* Neon (Ne): 0.001818%

* Helium (He): 0.000524%

* Methane (CH4): 0.00017% (also increasing due to human activity)

* Krypton (Kr): 0.000114%

* Hydrogen (H2): 0.00005%

* Xenon (Xe): 0.0000087%

* Ozone (O3): Variable, but typically around 0.000004%

Variable components:

In addition to the gases mentioned above, the atmosphere also contains variable components like:

* Water vapor (H2O): Ranges from near zero to 4% depending on location and weather conditions.

* Aerosols: Tiny particles of solid or liquid matter suspended in the air, including dust, pollen, smoke, and sea salt.

* Other trace gases: This includes gases like sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs), which are released from both natural and human sources.

Importance of atmospheric composition:

The composition of the atmosphere is crucial for life on Earth. Oxygen supports respiration, nitrogen is essential for plant growth, and carbon dioxide plays a role in the greenhouse effect, which helps to regulate the planet's temperature.

Changes in atmospheric composition:

Human activities have significantly altered the composition of the atmosphere, particularly through the release of greenhouse gases such as carbon dioxide and methane. These changes have contributed to global warming and other environmental problems.