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Name: Debbie B.
Status: Educator
Age: 30s
Location: N/A
Country: N/A
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 been developed.

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.

Andy Johnson

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