Oxygen is one of the most important and abundant elements on Earth. About 46 percent of the Earth's crust is oxygen. It is colorless and odorless and makes up about 20.95 percent of the atmosphere by volume. Oxygen exists in water as part of water molecule, in the atmosphere as a gas, in the Earth's crust and in an enormous variety of rocks and minerals. It can also be released from the plants through photosynthesis. Moreover it is very essential for life and is part of almost every biological molecule in our bodies. Without it, human life simply could not exist. …
