From the earliest times until now, people have believed that even though
millions of different kinds of material seem to exist in the world, most
things must be made up of combinations of just a few basic kinds of things.
There has not always been agreement, however, on what those basic kinds
of things are. One theory long ago was that the basic substances were earth,
water, air, and fire. Scientists now know that these are not the basic
substances. But the old theory seemed to explain many observations about
the world.
| See Content Standard G History and
Nature of Science (grades 9-12): Historical Perspectives.
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