It moderates the planet's temperature, reducing the extremes that occur on airless worlds. The atmosphere also protects us by absorbing and scattering harmful radiation from the sun and space. We are not normally aware of it but air does have weight. The column of air above us exerts pressure on us. This pressure at sea level is defined as one atmosphere.
Atmospheric pressure decreases rapidly with height.
This means that the pressure is 1 atmosphere at sea level, but 0.1 atmosphere at 16 km and only 0.01 atmosphere at 32 km. The density of air also decreases rapidly with altitude. People who normally live closer to sea level experience temporary breathing difficulties when traveling to these altitudes. The atmosphere is divided into layers based on temperature, composition and electrical properties. These layers are approximate and the boundaries vary, depending on the seasons and latitude.