If lava showed scientists that there is mantle, how do you know that there
is a core in the center of the Earth?
James
James,
Scientists know there is a mantle and a core, not because of
lava, but because of the way earthquake energy passes through the Earth.
When an earthquake occurs - like the one in Kobe, Japan recently - waves
of energy move in all directions away from the place where the Earth's
rocks broke. The speed that the waves travel depends on the type and
temperature of the rocks they pass through. By timing how long waves of
different sizes take to travel from the earthquake seismometers
around the world, scientists can begin to understand the nature of the rocks
buried deep within the Earth.
There are two important types of earthquake waves:
compression waves and
shear waves . Compression
waves pass through rock and liquids, but shear
waves can't pass through liquids.
Seismologists long
ago discovered
that shear waves do not pass through the central regions of the Earth;
therefore, the core of the Earth must be liquid!
Chuck Wood, University of North Dakota
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