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Correct, dinitrogen is the major component of the atmospheric gas mixture. The Earth's atmosphere includes several layers: the troposphere, the stratosphere, which includes the ozone layer, the mesosphere, and the outermost ionosphere where most atoms are ionized and where the aurora takes place. The atmosphere consists of about 79% dinitrogen, 20% dioxygen, and 1% other gases including ozone, carbon dioxide and others. When the Earth was formed some five billion years ago, it was too hot to retain its early atmosphere, consisting of helium, hydrogen, ammonia, and methane. Then, volcanoes erupted and emitted gases and formed the Earth's second atmosphere consisting of water vapor, carbon dioxide, and nitrogen. The water vapor formed clouds that produced rain, forming rivers, lakes, and oceans. These water reservoirs acted as sinks for the large amounts of carbon dioxide and through chemical and biological processes carbon dioxide became locked up in sedimentary rocks such as limestone. The nitrogen however, which is chemically rather inert, continued to accumulate in the atmosphere to the levels we see today.
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