On the periodic table, oxygen is the most abundant element in Earth's crust by mass.
Oxygen makes up about 46.6% of Earth's crust by mass, chiefly because it is bound into minerals such as silicates and metal oxides. Its atomic number is 8 and its symbol is O.
This answer refers specifically to the crust, not to the whole Earth or the universe. Silicon is the second-most abundant element in the crust by mass, while iron dominates much of Earth's core. Oxygen is also the most abundant element in the human body by mass, largely because water and many biomolecules contain it.
At ordinary conditions, elemental oxygen is a colorless gas that supports combustion but does not itself burn. Most atmospheric oxygen is molecular O2, while a smaller amount exists as ozone, O3.