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The lightest nuclei such as deuterium, helium, and a small amount of lithium were formed during a process called Big Bang nucleosynthesis. Big Bang nucleosynthesis refers to the production of nuclei other than those of the lightest isotope of hydrogen (hydrogen-1) during the early phases of the universe, shortly after the Big Bang. These light elements were formed within the first few minutes of the universe due to the high temperature and density conditions present at the time.

The elements heavier than helium in the periodic table through uranium are produced mainly through a process called stellar nucleosynthesis. Stellar nucleosynthesis occurs in stars during their lifecycle. When stars undergo nuclear fusion, they combine lighter elements to form heavier ones, releasing energy in the process. Through many fusion sequences, stars can produce elements up to iron (Fe) in their cores. For elements heavier than iron, they are formed during explosive events such as supernovae through a process called neutron capture. There are two primary processes of neutron capture: the slow process (s-process) and the rapid process (r-process). The s-process occurs in the late stages of a star's life, while the r-process is observed during supernovae and neutron star collisions. These processes contribute to the production of elements in the periodic table through uranium.