What are the main constituents of the earth's atmosphere in our time?
The present atmosphere of the earth is constituted mostly of molecular nitrogen (N2) and molecular oxygen (O2). Nitrogen is the most abundant gas, approximately 80% of the total volume. Oxygen makes up about 20%. Other gases exist in the atmosphere in a low percentage. (Of great concern is the enhancing in the amount of carbon dioxide because of human activity, the cause of the threatening global warming.)