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Hydrogen is the most abundant element in the universe, comprising about 75% of the universe's total chemical mass. The universe's hydrogen and helium were originally created beginning about three minutes after the Big Bang, in a ratio of about ten hydrogens to one helium, a balance which still exists today.This means hydrogen atoms are around 13.7 billion years old.
Later on, hydrogen and helium atoms began to coalesce into clumps. Once enough atoms gathered, the clump's own gravity caused them to heat up as the atoms rubbed together; eventually the material ignited, and stars were formed. Stars have nuclear fusion reactions at their core, and this reaction can create other, heavier elements. When a star runs out of fuel and dies, these elements are spread out into space. So carbon, silicon, oxygen, and all the other natural elements were created by stars, and are much younger (probably by several billion years) than hydrogen, which was created by the Big Bang.
The Big Bang nucleosynthesis is believed to be responsible for the formation of a heavier isotope of hydrogen known as deuterium (H-2 or D), the helium isotopes He-3 and He-4, and the lithium isotopes Li-6 and Li-7. Big Bang nucleosynthesis begins about three minutes after the Big Bang, when the universe has cooled down sufficiently to form stable protons and neutrons, after baryogenesis. Hence, the first Hydrogen atoms to form were probably [ (13.75 ± 0.17 billion years) - 3 min ] old. :D
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