What Are the Two Major Components of the Earth's Atmosphere?

By Falinia Adkins; Updated April 25, 2017
Despite its bad reputation, the greenhouse effect is necessary for life to thrive on Earth.

The Earth’s atmosphere reaches 372 miles from the Earth’s surface and performs an important function in keeping the Earth’s temperature in a range where life can thrive and reproduce. Without the atmosphere, which consists of several gases, the Earth’s temperature would drop 30 degrees or more making it impossible for natural grasses and trees to live and grow.


Nitrogen is the most prevalent gas, making up nearly 78 percent of the Earth’s atmosphere, which amounts to 4,000 trillion tons. Nitrogen comes from sources such as decaying matter and human fertilizers added to the ground. Interestingly enough, despite it being the most prevalent gas in the atmosphere, most organisms cannot utilize nitrogen in its atmospheric state. Therefore, living organisms that require nitrogen for protein synthesis must consume nitrogen through other means.


Oxygen is the second most prevalent gas of the Earth’s atmosphere making up 21 percent. However, the Earth’s atmosphere has not always contained this percentage of oxygen. It was not until 2 billion years ago when photosynthesizing bacteria called cyanobacteria began converting carbon dioxide to oxygen. Scientific American says it took another one billion years for those bacteria to make enough oxygen to affect the Earth’s atmosphere to enable the evolution of animals and change the amount of oxygen in the Earth’s atmosphere from zero to what it is today.

Interesting Facts

Nitrogen and oxygen were discovered in the same year. In 1772, Scottish physician Daniel Rutherford, despite its abundance, discovered the element nitrogen. Also during that same year, pharmacist Carl Scheele discovered oxygen, and referred to it as “fire air” because of its combustion properties. However, it was not until the 1800s when the scientist John Dalton discovered that the atmosphere consisted of various gases.


Global warming is a separate issue that is a result of excessive amounts of greenhouse gasses in the atmosphere. Factors that contribute to a depletion of the Earth’s atmosphere are the greenhouse gases, depletion of the ozone and deforestation.