ABSTRACT
Planet earth has a rare and unique atmosphere. The experts tells us that in the early years, some millions of years ago, the atmosphere was more like that on Venus and Mars, mainly CO2. So no doubt, the CO2 level has been much higher than today, but the difference is that there were no living creatures on the planet, and far from any human beings. Today we are enjoying an atmosphere with approximately 21% oxygen and 78% nitrogen + some other gases, among them about 0.03% carbon dioxide. At the same time, we have a rare balance in temperature. While the cosmos might experience some temperatures from several thousand degrees plus, down to a few hundred minus, we seldom find temperatures on earth outside ±50°C, and most people feel uncomfortable with temperatures below –20°C and above 40°C. Probably most people would set the range much narrower (Figure 3.1).
