Around 10,000 years ago, the planet's forest cover was at least twice what it is today, which means that forests are now emitting only half the amount of oxygen. Desertification and deforestation are rapidly accelerating this long-term loss of oxygen sources.

The largest flying creature alive today is the Andean condor Vultur gryphus. At maximum size it weighs about 22 pounds and has a wingspread of about 10 feet. But 65 million years ago in the late cretaceous period, the last age of dinosaurs, there was another larger flying animal, the giant pterosaur Quetzalcotalus. It had a wingspread of over 40 feet, the size of a small airplane. Other pterosaurs were also quite large. The pteranodons of the late jurassic period, the classic flying dinosaurs of magazine illustrations, had a maximum wingspan of about 33 feet. This presents a puzzle: how is it that the largest flying animals of the cretaceous were able to attain so much greater size than modern birds? There are severe physical limits associated with flight. It is difficult for large birds to generate enough lift to take off. Consider the well-known square-cube law: if you double the size of a bird by simple scaling, its wing area and associated lift go up by 22, or a factor of 4, while the body weight that must be lifted goes up by a factor of 23, or a factor of 8. When an evolving flying animal species increases in size the basic design must be altered to accommodate the reduced lift-to-payload ratio. But if anything, the pterosaurs were less well designed than modern birds. They lacked the birds' efficient keelbone muscle structure and the aerodynamic advantages of feathers. How, then, could pterosaurs have grown so large?

At a meeting of the Geological Society of America held last Fall in Phoenix, Robert Brenner of Yale University and Gary Landis of the U. S. Geological Survey reported the results of a QMS analysis of ancient air bubbles trapped in amber. They obtained a remarkable result. The atmosphere of the Earth 80 million years ago was discovered to have 50% more oxygen than modern air. Brenner and Landis found that for all gas samples taken from amber 80 million years old the oxygen content ranged between 25% to 35% and averaged about 30% oxygen. Cretaceous air was supercharged with oxygen.