The most abundant gas in the Earth's atmosphere is nitrogen, which makes up about 78% of the atmosphere’s composition. Oxygen is the second most abundant gas, accounting for around 21%. The remaining 1% consists of argon, carbon dioxide, and other trace gases. Nitrogen plays a crucial role in the environment, as it is a key component of amino acids and proteins essential for life. Atmospheric processes, including photosynthesis by plants, help regulate the levels of these gases, maintaining a balance that is vital for sustaining life on Earth.