Composition of the Atmosphere

• The atmosphere is composed of nitrogen (78%), oxygen(21%), carbon dioxide(0.04%) and rare other gases (1%) as well as ozone (0.000007%).
• Natural processes are in a state of balance which maintains the average composition of the atmosphere so that it only changes over long timescales - known as dynamic equilibrium. For example, photosynthesis and aerobic respiration are important processes, they roughly balance each other, but the rates at which they occur vary over different timescales so the concentration of each gas fluctuates around a mean concentration.
• Many of the processes that affect the atmosphere are interconnected, so if one changes it can cause changes in other processes. This means that human actions can trigger a sequence of events where a human action changes one process which can cause other processes to change.