Chemical element universe's 94 naturally occurring chemical elements are thought to have been produced by at least four cosmic processes. Most of the hydrogen, helium and a very small quantity of lithiumin the universe was produced primordially in the first few minutes of the Big Bang. Other three recurrently occurring later processes are thought to have produced the remaining elements. Stellar nucleosynthesis, an ongoing process inside stars, produces all elements from carbon through iron in atomic number, but little lithium, beryllium, or boron. Elements heavier in atomic number than iron, as heavy as uranium and plutonium, are produced by explosive nucleosynthesis in
Hydrogen Hydrogen Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed "protium" (name rarely used, symbol H), has one proton and no neutrons. The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless,