Timeline of Photosynthesis on Earth. Editors note: This story is part of a Feature The Color of Plants on Other Worlds from the April 2008 issue of Scientific American. Photosynthesis evolved early in Earthâs history. The rapidity of its emergence suggests it was no fluke and could arise on other worlds, too. As organisms released gases that changed the very lighting conditions on which they depended, they had to evolve new colors. 4.6 billion years ago -- Formation of Earth 3.4 billion years ago --First photosynthetic bacteria They absorbed near-infrared rather than visible light and produced sulfur or sulfate compounds rather than oxygen.
Causes of esophageal cancer. By Dr Ananya Mandal, MD. The exact causes of esophageal cancer are unknown. However, some risk factors raise the likelihood of acquiring esophageal cancer. Studies have shown that cigarette smoking and chronic alcohol consumption are the best known risk factors for esophageal cancer.
Esophageal cancer is a devastating disease. Although some patients can be cured, the treatment for esophageal cancer is protracted, diminishes quality of life, and is lethal in a significant number of cases. The principal histologic types of esophageal cancer are squamous cell carcinoma and adenocarcinoma. As squamous cells line the entire esophagus, squamous cell carcinoma can occur in any part of the esophagus; it often arises, however, in the upper half of the esophagus.