Bang, as the "soup" of free protons and neutrons which had initially been created in about a 6:1 ratio cooled to the point where nuclear binding was possible, almost all atomic nuclei to form were helium-4 nuclei. The binding of the nucleons in helium-4 is so tight that its production consumed nearly all the free neutrons in a few minutes, before they could beta decay, and left very few to form heavier atoms (especially lithium, beryllium, and boron). The energy of helium-4 nuclear binding per nucleon is stronger than in any of those elements (see nucleogenesis and binding energy), and thus no energetic "drive" was available to make elements 3, 4, and 5 once helium had been formed. It is barely energetically favorable for helium to fuse into the next element with a higher energy per nucleon (carbon). However, due to the rarity of intermediate elements, and extreme instability of beryllium-8 (the product when two 4He nuclei fuse), this process needs three helium nuclei striking each other nearly simultaneously (see triple alpha process). There was thus no time for significant carbon to be formed in the few minutes after the Big Bang, before the early expanding universe cooled to the temperature and pressure where helium fusion to carbon was no longer possible. This left the early universe with a very similar hydrogen–helium ratio as is observed today (3 parts hydrogen to 1 part helium-4 by mass), with nearly all the neutrons in the universe trapped in helium-4. All heavier elements—including those necessary for rocky planets like the Earth, and for carbon-based or other life—thus had to be produced, since the Big Bang, in stars which were hot enough to fuse elements heavier than hydrogen. All elements other than hydrogen and helium today account for only 2% of the mass of atomic matter in the universe. Helium-4, by contrast, makes up about 23% of the universe's ordinary matter—nearly all the ordinary matter that is not hydrogen (1H). See also Superfluid helium-4 Big Bang nucleosynthesis References External links Superfluid Helium-4 Interactive Properties Helium-04