Answer. The study of composition of atmosphere provides us the knowledge about significance of gases present in the atmosphere. Atmosphere is divided into four regions. Each region has its natural characteristics. Atmosphere is the envelope of different gases around the Earth. Major concentration of Na, O2 and Ar are present in atmosphere. The presence of CO2 and water vapours play a significant role in maintaining temperature of the atmosphere. Both of these gases are transparent to visible light but absorb infrared radiations emitted by the Earth's surface. Therefore, these gases absorb much of the outgoing radiations and warm the atmosphere. The presence of O2 in stratosphere saves us from dangerous UV radiations.