What's the third most common element?
What caught my eye was the oscillation in the abundancy graph, there is a tendency for even atomic number elements to be more abundant than odd atomic number elements.  Looking at the original Wikipedia article leads to the Oddo-Harkins rule http://en.wikipedia.org/wiki/Oddo%E2%80%93Harkins_rule.  There is more discussion on the stability of even vs odd atomic number elements here: http://en.wikipedia.org/wiki/Even_and_odd_atomic_nuclei.  From the latter link, roughly 60% of stable nuclei have an even number of protons and an even number of neutrons.  Only 2% have an odd number of protons and an odd number of neutrons.It would be nice if someone could explain any of the exceptions to the Oddo-Harkins rule, such as the dip at atomic number 44, Ruthenium.