Big Bang nucleosynthesis

In physical cosmology, the Big Bang nucleosynthesis was an event that happened during the Big Bang.^[1] It made elements heavier than hydrogen when the Universe was young. Most cosmologists believe that it happened roughly 10 seconds to 20 minutes after the Big Bang.^[2] It is also calculated to have made most of the helium in the Universe and a very small amount of lithium. It also made two radioactive isotopes. They are tritium and beryllium-7.