1. Origins: SolarSystem Elements
Oxygen is the most abundant element in the human body (about 65% by mass), calcium helps form and maintain healthy bones and teeth, and iron is a vital part of red blood cells that carry oxygen through the body. All of the oxygen in the Solar System comes from exploding massive stars. About half of the calcium and about 40% of the iron also come from these explosions, with the balance of these elements being supplied by explosions of smaller mass, white dwarf stars.(Illustration: NASA/CXC/SAO/K. Divona)

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2. The Periodic Table for Astronomy
A graphic representation of the abundances of the elements is shown in the "astronomers" version of the periodic table, vs the standard periodic table. What leaps out of the astronomers' table is that the simplest elements, hydrogen and helium, are far and away the most abundant.(Credit: NASA/CXC/M.Weiss)
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3. The Periodic Table
The periodic table of elements is an organized way of displaying information about the approximately 100 chemical building blocks of the Universe. The number that is above the letter in each box is the atomic number for that element. It represents the number of protons in one atom of the element. (Credit: NASA/CXC/M.Weiss)
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4. Abundance Pie Chart
This pie chart illustrates the average abundance by mass of the various elements in the Universe (called the cosmic abundances) in parts per 10,000. The large abundance of hydrogen and helium and the small abundances of all the rest of the elements (about 2% of the total), as well as evidence from other observations, indicate that the Universe was once composed on just one element, hydrogen, and that the nuclear fusion reactions that produce the heavier elements have proceeded very slowly over the 13.7 billion year history of the Universe. This is a good thing, since otherwise the Sun would have likely burned out long ago. (Credit: NASA/CXC/M.Weiss)
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