The atmosphere is the layer of gases wrapped around Earth. It is thin. If Earth were an apple, the atmosphere would be its skin. Yet it holds the oxygen we breathe, shields us from radiation, and traps enough heat to keep the planet habitable. Without it, surface temperatures would average around minus 18 degrees Celsius.

It has layers. The troposphere, closest to the ground, contains most of the weather. Above it sits the stratosphere, home to the ozone layer that blocks ultraviolet radiation. Higher still are the mesosphere, thermosphere, and exosphere, each with different chemistry and temperature profiles. The boundaries are not sharp. They blend.

Human activity is changing the atmosphere's composition. Carbon dioxide concentrations have risen from about 280 parts per million before industrialization to over 420 today. Methane, nitrous oxide, and other greenhouse gases have also increased. These changes trap extra heat and drive climate change. The atmosphere is a global commons. What one country emits affects everyone.

Main layers

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere