Oxygen (O2)

Oxygen (O2) makes up 21 percent of the earth's atmosphere, supports life and makes combustion possible. As it is the most abundant of all elements on earth, oxygen comprises 85 percent of its oceans, a component of most rocks and minerals, and 46 percent of its solid crust. In addition, it constitutes 60 percent of the human body.

Colorless, odorless and tasteless and a specific gravity of 1.105 making it slightly heavier than air. When cooled to its boiling point of -297F (-183C), oxygen becomes a transparent, pale blue liquid that is slightly heavier than water.