Carbon dioxide is a colorless and non-flammable gas at normal temperature and pressure. Although much less abundant than nitrogen and oxygen in Earth's atmosphere, carbon dioxide is an important constituent of our planet's air.A molecule of carbon dioxide (CO 2) is made up of one carbon atom and two oxygen atoms.Carbon dioxide is an important greenhouse gas that helps to trap heat in our atmosphere. Without it, our planet would be inhospitably cold. molecule of carbon dioxide (CO 2) is made up of one carbon atom and two oxygen atoms. Carbon dioxide is an important greenhouse gas that helps to trap heat in our atmosphere. Without it, our planet would be inhospitably cold.