Exploring the Earth’s Interior

How did we learn about the Earth’s interior? I will channel my inner Isaac Asimov here, and explain how we did it.

One can do so by digging downward, and some mines have been dug to some impressive depths by ordinary standards. The champions are currently the TauTona and Mponeng gold mines near Johannesburg, South Africa, going down some 4 km (2.5 mi). But that’s barely a scratch compared to the Earth’s average radius of about 6371 km (3959 mi).

There are also tunnels excavated by various natural effects — caves — but those don’t extend very far down either. The deepest known cave is the Krubera Cave in the Abkhazia district of Asian Georgia, at about 2.2 km (1.4 mi).

So we have to use more indirect methods: magnetism, earthquake waves, gravity, eruptions and overthrusts, and meteorite composition.

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