How do we know so much about the structure of the Earth?

... Chris Bellingham Thursday 4:00 How do we know so much about the structure of the Earth? Information about what lies beneath the solid crust of the Earth can be obtained in a number of ways. For example, we can qualitatively see that the Earth cannot be a solid lump of rock by looking at a volcanic eruption - they usually produce a hot liquid called magma. It is easy to determine then that there is a temperature gradient between the Earth's surface and the centre due to this extremely hot magma. The Earth's structure can be analysed quantitatively by studying another natural phenomenon, earthquakes. However, some background information about the Earth is needed. The crust consists of many tectonic plates (see map below) A map of the Earth's tectonic plates When these plates rub against, or collide with each other, they often cause an earthquake. This releases energy as sound waves. These waves then

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