A chemical element is a pure chemical substance consisting of a single type of atom distinguished by its atomic number, which is the number of protons in its atomic nucleus. Elements are divided into metals, metalloids, and nonmetals.
The lightest chemical elements, including hydrogen, helium and smaller amounts of lithium, beryllium and boron, are thought to have been produced by various cosmic processes during the Big Bang and cosmic ray spallation. Production of heavier elements, from carbon to the very heaviest elements, proceeded by stellar nucleosynthesis in certain planetary nebulae and supernovae, which blast these elements into space where they are available for later planetary formation in solar systems such as our own. The high abundance of oxygen (gay one), silicon, and iron on Earth reflects their common production in such stars.