Atmosphere of Earth development of animals. Today's atmosphere contains 21% oxygen, which is great enough for this rapid development of animals. "Air pollution" is the introduction into the atmosphere of chemicals, particulate matter or biological materials that cause harm or discomfort to organisms. Stratospheric ozone depletion is caused by air pollution, chiefly from chlorofluorocarbons and other ozone-depleting substances. The scientific consensus is that the anthropogenic greenhouse gases currently accumulating in the atmosphere are the main cause of global warming. On October 19, 2015 NASA started a website containing daily images of the full sunlit side of Earth on http://epic.gsfc.nasa.gov/. The images are taken
Life on Titan hydrogen concentration in the upper and lower atmosphere. Strobel found that the hydrogen concentration in the upper atmosphere is so much larger than near the surface that the physics of diffusion leads to hydrogen flowing downwards at a rate of roughly 10 molecules per second. Near the surface the downward-flowing hydrogen apparently disappears. Another paper released the same month showed very low levels of acetylene on Titan's surface. Chris McKay agreed with Strobel that presence of life, as suggested in McKay's 2005 article, is a possible explanation for the findings about hydrogen and acetylene, but also cautioned that other explanations