If there’s one thing that the observable universe has a whole lot of, it’s hydrogen. Cosmological observations and careful astronomical calculations indicate that roughly 75 percent of baryonic (normal) matter (by mass) in the universe is composed of hydrogen.
This puts it leaps and bounds ahead of the next nine most-abundant elements: helium, oxygen, carbon, neon, iron, nitrogen, silicon, magnesium, and sulfur. The mass of all those elements combined doesn’t even begin to approach half the amount of hydrogen.
Helium, while we’re talking about the matter, is no slouch though. Even though it comes in a distant second to hydrogen, the two elements make up a staggering 99.9 percent of baryonic (normal) matter in the known universe.
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