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 <a href="http://en.wikipedia.org/wiki/Oddo%E2%80%93Harkins_rule" rel="nofollow">http://en.wikipedia.org/wiki/Oddo%E2%80%93Harkins_rule</a>.  There is more discussion on the stability of even vs odd atomic number elements here: <a href="http://en.wikipedia.org/wiki/Even_and_odd_atomic_nuclei" rel="nofollow">http://en.wikipedia.org/wiki/Even_and_odd_atomic_nuclei</a>.  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.<p>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.