Name: Debbie B.
Date: January 6, 2004
My fourth grade class and I would like to know how
scientists know what makes up the layers of the Earth.
Although Earth has a diameter of roughly 8000 miles, scientists have only
drilled down for about seven miles into the crust. So, no one has directly
observed the interior of the planet at greater depths. Consequently, the
structure of Earth's interior has to be inferred from careful observation of
rocks and their structure on the surface and the bottom of the oceans. This
sort of work is generally done by geologists. Scientists called geophysists
study the behavior of seismic waves as they pass through the center of the
Earth and variations in magnetism and gravity. Although scientific
knowledge on this topic is expanding all the time, much is still unknown.
For instance, although the concept of continental drift is now widely
accepted, a definitive explanation of why the continents are moving has not
Perhaps you could explain this concept to fourth graders by setting up some
experiments where they have to figure out what's inside container without
opening it. They could weigh it, take its temperature, tap on it, wave a
metal detector over it, etc.
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