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
Greenhouse and icehouse Earth the greenhouse gas concentration, the Earth would be heading toward a glacial period. Predicted changes in orbital forcing suggest that in absence of human-made global warming the next glacial period would begin at least 50,000 years from now (see Milankovitch cycles). But due to the ongoing anthropogenic greenhouse gas emissions, the Earth is instead heading toward a greenhouse Earth period. Permanent ice is actually a rare phenomenon in the history of the Earth, occurring only in coincidence with the icehouse effect, which has affected about 20% of Earth's history. Greenhouse and icehouse Earth Throughout the Phanerozoic history of the Earth,