The three main gases found in the Earth's air are nitrogen, oxygen and water vapor. A typical volume of air at sea level at 15 degrees Celsius contains approximately 78 percent nitrogen, 21 percent oxygen and between 1 and 5 percent water vapor.
As the most abundant element in the atmosphere, nitrogen is essential for life and is a component of genetic material, amino acids and proteins. When lightning strikes, it causes the nitrogen in air to combine with water and form ammonia, or NH3, and nitrates, or NO3. These two compounds can be used by plants as a nutrient as part of a process called the nitrogen cycle.