“The two most common elements in the universe are hydrogen and stupidity.” -Harlan Ellison
Shortly after the Big Bang, the Universe was filled with 99.99999993% hydrogen and helium, with the rest being lithium. But stars change everything, by fusing those elements — the lightest ones — into heavier ones, climbing the periodic table and enriching the Universe with its contents.
After billions of years of star formation and nuclear fusion, a new 3rd most common element has emerged, and it isn’t carbon — formed from helium fusion — which only clocks in at number 4. Instead, the winner is oxygen, thanks to the intricacies of stellar reactions, and which may some day crack the top two in the far future. Lithium isn’t even close to being in the top 10 anymore.