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Oxygen is a well-known colourless, odourless gas. It is so reactive that it forms oxides with virtually all elements except He, Ne, Ar, Kr. Being the most abundant element in the Earth's crust, oxygen is present in silica (SiO4) and the oceans (H2O). The gas also makes up 1/5 of our atmosphere.
Above the Earth's atmosphere, an allotrope of oxygen – ozone – is found. Whereas the oxygen that we breathe is a molecule composed of two oxygen atoms (O2), ozone consists of three oxygen atoms (O3). Although ozone is toxic, this vital layer surrounding the Earth's atmosphere helps prevent harmful ultraviolet (UV) radiation from reaching the Earth's surface. Currently, scientists are concerned with the issue of ozone depletion. The effect of certain chemicals and human activity has created "holes" in the ozone layer in the Earth's polar regions. It is believed that a 5% increase in these "holes" will cause a 10% increase in the penetration of UV rays through the Earth's atmosphere.
Biologically, oxygen is extremely important to all vertebrates as it is required to sustain biological processes, such as metabolism. Not only is oxygen present in the air we breathe, but also, it is a constituent of DNA – life's blueprint. If our blood level of oxygen is lowered, many of our bodily processes may be disrupted, and our brain does not function as well causing us to feel tired and distracted. Research aimed at improving the air quality in indoor environments is underway at the National Research Council Canada (NRC). The NRC's Institute for Research Construction is striving to develop strategies that will lead to better ventilation and higher indoor air quality.