The atmosphere of Earth is composed of nitrogen, oxygen, argon, carbon dioxide, and other gases. Together, these gases form a layer that protects the planet from the Sun's ultraviolet radiation and from most meteorites. The atmosphere also has a profound effect on the climate of Earth.
Earth's atmosphere consists of 78 percent nitrogen, 21 percent oxygen, and trace amounts of water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Argon makes up about 0.93 percent of the air by volume. Carbon dioxide levels have increased over time due to human activity such as burning fossil fuels like coal and oil.
The atmospheric pressure at sea level is about 1013 millibars or 14.7 pounds per square inch. The average temperature is 15 degrees Celsius (59 degrees Fahrenheit), but it can range from -56 degrees C (-69 F) on a cold winter night to 37 degrees C (99 F) in the shade on a hot summer day