Earth's atmosphere consists primarily of nitrogen (N2), making up about 78% of its volume. Oxygen (O2) comes next at around 21%, while argon (Ar) accounts for about 0.93%. Other gases, including carbon dioxide (CO2), neon (Ne), helium (He), methane (CH4), and hydrogen (H2), are present in trace amounts. The atmosphere also contains variable amounts of water vapor and aerosols, which are tiny particles of solid or liquid matter suspended in the air.