“It is the function of science to discover the existence of a general reign of order in nature and to find the causes governing this order. And this refers in equal measure to the relations of man – social and political – and to the entire universe as a whole.” -Dmitri Mendeleev
When the Universe was first born, all we had was hydrogen and helium, with a trace amount of lithium and absolutely nothing else. 13.8 billion years later, hydrogen is still #1 in the Universe and helium is still #2, but lithium isn’t close to #3 anymore: more than two dozen elements have passed it. The key? Stars!
An artist’s impression of the environment in the early Universe after the first few trillion stars have formed, lived and died. Lithium is no longer the third most abundant element at this point. Image credit: NASA/ESA/ESO/Wolfram Freudling et al. (STECF).
Over billions of years, nuclear fusion in the cores of stars have built up all the naturally occurring elements we know of in the periodic table. You might think that since three heliums can fuse together to make carbon, that would be the third most common element in the Universe. And it’s close: carbon comes in at #4. But another element has it beat.
At the end of their lives, massive stars eject their outer layers back into the interstellar medium, enriching the Universe with elements beyond hydrogen and helium. Image credit: H. Bond (STScI), R. Ciardullo (PSU), WFPC2, HST, NASA.