Two miles beneath the surface, in this South African gold mine, bacteria of the firmicutes clan have taken up residence. The advantages of this extreme real estate? The tight space, heat, and high pressure are not appealing to most species. Since it is dark, you can’t see the gold, so that selling point is pretty weak. But where you live is a personal choice, and has to be respected. Different strokes for different folks.
That said, taking up permanent residence two miles down takes some getting used to. Every living thing needs a source of chemical energy to run all those cellular processes. Photosynthesis? No sun. No way. Oxygen for respiration? There isn’t any. Gasp! What is their secret? Use hydrogen liberated from underground water by the decay of uranium. OK! That should last a while! Use the same heat source that keeps the depths hot so that our earth can maintain its lively geology with volcanoes, earthquakes, plate tectonics, etc. What an idea! The big question: what else is down there? Who is down there?