Quick, what are the ten most abundant elements in the Galaxy?
Guessing number 1 isn't difficult. We know Hydrogen was created in the Big Bang and it is still everywhere you look. Since Hydrogen is fused into Helium, it is natural to pick Helium as #2. That's correct but probably most of the helium in the Galaxy was formed in the Big Bang. Although Helium is found on earth it was actually first discovered in the Sun.
After Hydrogen and Helium show up as 1-2 in the Periodic Chart of Elements and also in actual abundance, it is tempting to keep going down the chart. But that would be wrong. Lithium is most likely another Big Bang product but rarely. Knowing that, you would be wise to skip over Beryllium and Boron. Carbon, anyone? Nope. Oxygen is twice as abundant as Carbon. Oxygen and Carbon, the next most abundant element, are both created by fusing (or "burning") Helium.
At this point, if we are guessing the #5 element on our top 10 list, we might be tempted to look at Neon. Once a star finishes fusing Helium it will start fusing Carbon into Neon. That turns out to be correct. If instead, you were thinking that CHON is the formula for life, Nitrogen must be high on the list. It is, #6 to be exact and nearly as abundant as Neon. Nitrogen is actually created as one of the less likely by-products of Hydrogen fusing.
So, with the six most abundant elements we have everything we need for life, balloons and advertising signs. What's #7. Magnesium, the 12th element in the Periodic Table which is created by Neon and Carbon burning. Next comes Silicon. In the #9 position we find Iron, the heaviest and last element that any sun will create through fusion. Everything heavier than Iron is only created in the supernovae explosion itself. In fact, it is the creation of Iron that triggers the supernova. The number #10 element is Sulphur. Silicon and Sulphur are created during Oxygen burning.
So that's your top 10 list of the most common elements in the Galaxy. Hydrogen and Helium are spread throughout the Galaxy as the result of the Big Bang. The others need a supernovae to populate the Galaxy. Information for this article came from http://www.talkorigins.org/faqs/supernova/#BM82 which in turn came from Ken Croswell's book "Alchemy of the Heavens" (Doubleday 1996).
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