The atmosphere is the gaseous envelope of a planet. It surrounds the planet and protects it from the vacuum of space. The Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.1% carbon dioxide, and small amounts of other gases. Water vapor is also present in the atmosphere, but its concentration varies depending on location and weather conditions.
The atmosphere has several important functions. It helps to regulate the temperature of the planet by trapping heat from the sun and reducing heat loss from the surface of the planet. The atmosphere also protects us from harmful ultraviolet radiation from the sun and helps to moderate our climate by redistributing heat around the globe through atmospheric circulation patterns. Additionally, the atmosphere provides a medium for plants to photosynthesize and for animals to breathe.
The composition of Earth’s atmosphere has changed over time due to both natural processes and human activity. For example, early in Earth’s history, there was much more carbon dioxide in the atmosphere than there is today. This greenhouse gas trapped heat and made Earth’s surface much warmer than it is now. Over time, some of that carbon dioxide was taken up by plants through photosynthesis and turned into oxygen gas, which slowly began to accumulate in the atmosphere (a process known as oxygenation). Today, human activities such as burning fossil fuels are increasing levels of atmospheric carbon dioxide once again, resulting in increased global temperatures (known as climate change).