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 cooler globally. The Earth is currently in an icehouse stage, as ice sheets are present on both poles and glacial periods have occurred at regular intervals over the past million years. The causes of an icehouse state are much debated, because not much is really known about the transition periods between greenhouse to icehouse climates and what could make the climate so different. One important aspect is clearly the decline of CO in the atmosphere, possibly due to low volcanic activity. Other important issues are the movement of the tectonic plates and the opening and closing of oceanic gateways. These