The Earth's atmosphere is composed of a mixture of various gases. Although the composition of the atmosphere remains relatively constant, there can be slight variations in the concentration of certain gases. Here are the major gases and their approximate percentage in the Earth's atmosphere:

1. Nitrogen (N2): Nitrogen is the most abundant gas in the atmosphere by volume, making up approximately 78% of the total atmospheric composition.

2. Oxygen (O2): Oxygen is the second most abundant gas and is essential for respiration and various life processes on Earth. It constitutes around 21% of the atmosphere.

3. Argon (Ar): Argon is a noble gas that is third in abundance in the atmosphere. It comprises roughly 0.93% of the total volume.

4. Carbon Dioxide (CO2): Carbon dioxide is a greenhouse gas that plays a significant role in regulating the Earth's temperature. It currently makes up about 0.041% of the atmosphere.

5. Neon (Ne): Neon is another noble gas present in trace amounts in the atmosphere, accounting for approximately 0.0018% of the total volume.

6. Helium (He): Helium is a noble gas that is lighter than air. Although present in trace amounts, helium constitutes roughly 0.0005% of the atmosphere.

7. Methane (CH4): Methane is a hydrocarbon gas that is also a greenhouse gas. It contributes about 0.0002% of the atmosphere's composition.

Various other gases are present in the atmosphere in even smaller quantities, including hydrogen (H2), nitrous oxide (N2O), ozone (O3), sulfur dioxide (SO2), carbon monoxide (CO), and water vapor (H2O). Additionally, the atmosphere may contain certain pollutants or aerosols resulting from human activities and natural processes.

It's important to note that while the overall composition of the atmosphere remains relatively consistent, human activities, such as the burning of fossil fuels and deforestation, can alter the concentrations of certain gases, particularly greenhouse gases, with implications for climate change and global temperatures.