Model: Suppose that you know very little about Earth’s interior and wanted to find out how accurate Halley’s model was. How would you go about evaluating the validity of the model? What sort of evidence would you need to collect and how could you collect it? 

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igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

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