THE CHEMICAL DEFINITION OF THE WORD "ELEMENT":
element: any one of over 100 known distinct varieties of matter which, singly or in combination, compose substances of all kinds.
Another way of saying it is that an element is matter which consists of atoms, all of which have the same atomic number (the same number of protons or electrons). All known elements are listed on our Periodic Chart page.
Astrophysicists tell us that during the first three minutes of the existence of the Universe, immediately after the Big Bang, all the matter of the Universe existed in the form of atoms of the three lightest elements -- hydrogen, helium and lithium. These are the first three elements listed in the Periodic Chart. Today we recognize over 100 elements, and those 100+ elements contribute most of the mass of everything we can see and feel. Therefore, where did all the "heavier elements," such as oxygen, carbon and gold, come from?
If you need to review the basic facts about electrons, protons, atoms, molecules, elements, and the like, a good place to begin is About.com's Basic Chemistry Page. For more information on nucleosynthesis, visit Milky-Way.com's star-evolution page page.
All elements heavier than lithium were synthesized in stars that existed for millions of years -- not during the first moments of the Big Bang. When massive stars grow old, they burn helium to carbon, oxygen, silicon, sulfur, and iron. Elements heavier than iron are produced in two ways:
1: in the outer envelopes of super-giant stars
2: in the explosion of supernovae
These heavier elements were scattered throughout the Universe when the huge stars in which they were formed exploded.
In places, clouds of this mixed-up debris coagulated into spiraling systems that eventually developed into solar systems like ours -- the sun with its planets.
Therefore, you, I, and by far the greatest part of everything we see and feel on Earth and when we look into our night sky is composed of stardust -- stardust consisting of elements scattered from exploding stars that went through their entire evolution of birth, growth and death long before our solar system began forming. The term nucleosynthesis refers to this star-based formation of heavier elements from the fusion of lighter elements.
Now we're up to the point where we have an Earth made from elements. One of the favorite science essays I read when I was a kid was one by Isaac Asimov. Though it appeared in the July, 1961 issue of The Magazine of Fantasy and Science Fiction, it wasn't fantasy or science fiction at all. It was called "Recipe for a Planet," and it listed the major elements of the Earth's crust, presented in order of percentage by weight. That "recipe" is at the right. All the percentages don't add up to 100% because the Periodic Chart's remaining ninety-odd elements, such as gold, barium and molybdenum, occur in very small amounts. In the recipe, notice that the three lightest elements, those created during the Big Bang itself -- hydrogen, helium and lithium -- don't even appear. Thus nearly all the Earth's crust, when considered by weight, is made of elements from exploded stars... To see the Periodic Chart listing all the known elements, click here.
So this is where the basic "stuff" in our backyards comes from -- the dirt, most of the material from which the plants and animals are made, even the air and water. It's star stuff, and the story of this backyard-located, star-originated stuff is just beginning, as you'll see on our other geology pages.