A. 10,000
B. 20,000
C. 30,000
D. 40,000
The Kola Superdeep Borehole on the Kola peninsula of Russia reached 12,262 metres (40,230 ft) and is the deepest penetration of the Earth’s solid surface. The German Continental Deep Drilling Program at 9.1 kilometres (5.7 mi) has shown the earth crust to be mostly porous.
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