| Introduction |
| Hydrogen, H, the
lightest atom, is said to be the original atom
in the universe, and hydrogen atoms make up
more than 90 % of the atoms in the known universe.
Heavier atoms are produced in stars, which are
massive collections of hydrogen atoms pulled
together by gravitational forces. The great
pressures deep in a star’s interior cause hydrogen
atoms to fuse to heavier atoms. |
| With the exception
of hydrogen, therefore, all the atoms that occur
naturally on the earth—including those in our
body—are the products from the interiors of
stars. A rough composition of earth’s crust
is shown below. |
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