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
Reducing atmosphere had a reducing atmosphere, along with Mars and Venus. This would have proven to be a good environment for "Cyanobacteria" to evolve the first photosynthetic metabolic pathways which gradually increased the oxygen portion of the atmosphere, changing it to what is known as an oxidizing atmosphere. With increased levels of oxygen, the evolution of the more efficient aerobic respiration might have been enabled, allowing animal life to evolve and thrive. Though most scientists conceive of the early atmosphere as reducing, a 2011 article in "Nature" found that cerium oxidation in zircon—which comprises the oldest rocks on Earth at roughly 4.4